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Main
Date: 27 Jun 2007 11:22:19
From: Tom Nakashima
Subject: Re: Safe to lengthen a chain?
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> <jobst.brandt@stanfordalumni.org> wrote in message
> news:4681b1b4$0$14130$742ec2ed@news.sonic.net...
>>
>> Try to imagine how unusual it is that the forward roller of the
>> PowerLink was positioned on the entry to the sprocket so that when the
>> chain skipped, the advancing length of following chain, inertially
>> pushed the chain forward against the relatively immobile PowerLink
>> while the chain line was just right to cause the cover plate to be
>> deflected inward enough to clear the locking contour of the stepped
>> release slot. I reported this because it was such an unusual
>> mechanical coincidence of events but realized that no one understood
>> or cared what occurred from the silence that followed.
>>
>> Jobst Brandt
>
That is one magic PowerLink
Sorry I couldn't resist:
The Magic Bullet Theory by Jim Garrison (Kevin Costner) from the Movie JFK:
The magic bullet enters the President's back, headed downward at an angle of
17 degrees. It then moves upward in order to leave Kennedy's body from the
front of his neck -- his neck wound number two -- where it waits 1.6
seconds, turns right and continues into Connally's body at the rear of his
right armpit -- wound number three. Then, the bullet heads downward at an
angle of 27 degrees, shattering Connally's fifth rib and leaving from the
right side of his chest -- wounds four and five. The bullet continues
downward and then enters Connally's right wrist -- wound number six --
shattering the radius bone. It then enters his left thigh -- wound number
seven -- from which it later falls out and is found in almost "pristine"
condition on a stretcher in a corridor of Parkland Hospital.
That is one magic bullet.
The Magic Loogie Theory by Jerry Seinfeld
Newman, Kramer, if you'll indulge me.
According to your story Hernandez passes you and starts walking up the ramp.
Then you say you were struck on the right temple.
The spit then proceeds to ricochet off the temple striking Newman between
the third and forth rib.The spit then came off the rib made a right turn
hitting Newman in the right wrist causing him to drop his baseball cap.
The spit then splashed off the wrist, Pauses... In mid air mind you...-
Makes a left turn, and lands on Newman's left thigh.
That is one magic loogie.
-tom
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Date: 30 Jun 2007 20:09:33
From: Johnny Sunset
Subject: Tire filling fluids (was: Safe to lengthen a chain?)
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On Jun 30, 3:12 am, Sandy Leurre wrote:
> ...Those wheels with the same hubs, spokes, rims, tires and tubes
> (occasionally filled with water or bourbon)...
Or milk: <http://groups.google.com/group/rec.bicycles.tech/msg/
c1a9f571ffd02438?dmode=source&hl=en > and/or <http://groups.google.com/
group/rec.bicycles.tech/msg/a82a691763ff4c16?dmode=source&hl=en >.
Was Jobst's Swiss milk from a Brown Swiss? Would milk from a different
breed have worked better or worse? All we have around here are
Holstein-Friesians (in great abundance), so it is hard to experiment.
--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful
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Date: 29 Jun 2007 21:11:08
From:
Subject: Re: Safe to lengthen a chain?
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On Jun 29, 1:33 pm, jobst.bra...@stanfordalumni.org wrote:
> Carl Fogel writes:
> >> As I said, you apparently have not experienced chain skip on worn
> >> sprockets, especially one that barely skips and requires high chain
> >> tension to do so.
> > [snip]
> > Comments like that are what make me skeptical of so much else that
> > you say.
>
> How else can you explain the reinterpretation of the event to picture
> things that cannot occur. Either you are working at misinterpreting
> what I wrote or you don't understand the phenomenon. Take your pick.
You already know which. From a recent interpretation of a plastic
spoke protector:
-----
"This wear supports Trevor's claim a few years ago about spokes
worn a third of the way through."
I think the linkage is unambiguous enough to leave no doubt about what
was unbelievable.
Don't patronize when it is your willful misinterpretation.
-----
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Date: 27 Jun 2007 17:53:49
From: Johnny Sunset
Subject: Re: Safe to lengthen a chain?
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On Jun 27, 1:22 pm, Tom Nakashima wrote:
> ...
> The Magic Bullet Theory by Jim Garrison (Kevin Costner) from the Movie JFK:
>
> The magic bullet enters the President's back, headed downward at an angle of
> 17 degrees. It then moves upward in order to leave Kennedy's body from the
> front of his neck -- his neck wound number two -- where it waits 1.6
> seconds, turns right and continues into Connally's body at the rear of his
> right armpit -- wound number three. Then, the bullet heads downward at an
> angle of 27 degrees, shattering Connally's fifth rib and leaving from the
> right side of his chest -- wounds four and five. The bullet continues
> downward and then enters Connally's right wrist -- wound number six --
> shattering the radius bone. It then enters his left thigh -- wound number
> seven -- from which it later falls out and is found in almost "pristine"
> condition on a stretcher in a corridor of Parkland Hospital.
>
> That is one magic bullet....
Ridiculous. Everyone knows that Kennedy, to avoid going to prison and
to preserve his reputation for posterity, traveled back in time, stood
on the grassy knoll, and shot his other self, at which point he of
course ceased to exist, which is why the evidence of the other shooter
could not be found.
--
Tom Sherman - Holstein-Friesland Bovinia
"It's cold outside, there's no kind of atmosphere, I'm all alone, more
or less. Let me fly far away from here. Fun, fun, fun in the sun, sun,
sun."
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Date: 27 Jun 2007 18:45:35
From: Tim McNamara
Subject: Re: Safe to lengthen a chain?
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In article <f5u9sr$r3v$1@news.Stanford.EDU >,
"Tom Nakashima" <tom@slac.stanford.edu > wrote:
> > <jobst.brandt@stanfordalumni.org> wrote in message
> > news:4681b1b4$0$14130$742ec2ed@news.sonic.net...
> >>
> >> Try to imagine how unusual it is that the forward roller of the
> >> PowerLink was positioned on the entry to the sprocket so that when
> >> the chain skipped, the advancing length of following chain,
> >> inertially pushed the chain forward against the relatively
> >> immobile PowerLink while the chain line was just right to cause
> >> the cover plate to be deflected inward enough to clear the locking
> >> contour of the stepped release slot. I reported this because it
> >> was such an unusual mechanical coincidence of events but realized
> >> that no one understood or cared what occurred from the silence
> >> that followed.
> >>
> >> Jobst Brandt
> >
>
> That is one magic PowerLink Sorry I couldn't resist:
>
> The Magic Bullet Theory by Jim Garrison (Kevin Costner) from the
> Movie JFK:
>
> The magic bullet enters the President's back, headed downward at an
> angle of 17 degrees. It then moves upward in order to leave Kennedy's
> body from the front of his neck -- his neck wound number two -- where
> it waits 1.6 seconds, turns right and continues into Connally's body
> at the rear of his right armpit -- wound number three. Then, the
> bullet heads downward at an angle of 27 degrees, shattering
> Connally's fifth rib and leaving from the right side of his chest --
> wounds four and five. The bullet continues downward and then enters
> Connally's right wrist -- wound number six -- shattering the radius
> bone. It then enters his left thigh -- wound number seven -- from
> which it later falls out and is found in almost "pristine" condition
> on a stretcher in a corridor of Parkland Hospital.
>
> That is one magic bullet.
What's "magical" is that you appear to think Oliver Stone's movie was
factual, if you're citing it in this context. Surely there is a more
reasonable argument than citing conspiracy theory fantasy.
I understand the resistance to Jobst's explanation as I was startled by
it, too. It's hard to picture a flexible chain pushing the snap link
together causing it to open. I don't have a good alternative theory.
The notion that the snap link was just misintalled seems like a
non-starter to me: either it would have been snapped into the locked
position the first time it came under tension, in which case only the
noise would have been noticed; or it would have been simply pulled apart
the first time it came under tension- probably whacking Jobst in the leg
in the process and stopping him before the end of the driveway; or it
would have jammed in the jockey wheel cage due to the pitch being too
short, also stopping him before the end of the driveway.
When a chain skips a tooth on a cog, there's a lot of force and the
lower run usually shows a large waveform excursion, often also slapping
the derailleur forwards and upwards. Would there be enough force in
that to knock the snap link open? I don't know. It would certainly be
a freak occurrence.
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Date: 28 Jun 2007 06:48:32
From: Tom Nakashima
Subject: Re: Safe to lengthen a chain?
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"Tim McNamara" <timmcn@bitstream.net > wrote in message
news:timmcn-5B3CD4.18453527062007@news.iphouse.com...
> In article <f5u9sr$r3v$1@news.Stanford.EDU>,
> "Tom Nakashima" <tom@slac.stanford.edu> wrote:
>
>> > <jobst.brandt@stanfordalumni.org> wrote in message
>> > news:4681b1b4$0$14130$742ec2ed@news.sonic.net...
>> >>
>> >> Try to imagine how unusual it is that the forward roller of the
>> >> PowerLink was positioned on the entry to the sprocket so that when
>> >> the chain skipped, the advancing length of following chain,
>> >> inertially pushed the chain forward against the relatively
>> >> immobile PowerLink while the chain line was just right to cause
>> >> the cover plate to be deflected inward enough to clear the locking
>> >> contour of the stepped release slot. I reported this because it
>> >> was such an unusual mechanical coincidence of events but realized
>> >> that no one understood or cared what occurred from the silence
>> >> that followed.
>> >>
>> >> Jobst Brandt
>> >
>>
>> That is one magic PowerLink Sorry I couldn't resist:
>>
>> The Magic Bullet Theory by Jim Garrison (Kevin Costner) from the
>> Movie JFK:
>>
>> The magic bullet enters the President's back, headed downward at an
>> angle of 17 degrees. It then moves upward in order to leave Kennedy's
>> body from the front of his neck -- his neck wound number two -- where
>> it waits 1.6 seconds, turns right and continues into Connally's body
>> at the rear of his right armpit -- wound number three. Then, the
>> bullet heads downward at an angle of 27 degrees, shattering
>> Connally's fifth rib and leaving from the right side of his chest --
>> wounds four and five. The bullet continues downward and then enters
>> Connally's right wrist -- wound number six -- shattering the radius
>> bone. It then enters his left thigh -- wound number seven -- from
>> which it later falls out and is found in almost "pristine" condition
>> on a stretcher in a corridor of Parkland Hospital.
>>
>> That is one magic bullet.
>
> What's "magical" is that you appear to think Oliver Stone's movie was
> factual, if you're citing it in this context. Surely there is a more
> reasonable argument than citing conspiracy theory fantasy.
Actually I enjoyed Stone's myth but thought Jerry Seinfeld's theory of the
magic loogie was factual.
>
> I understand the resistance to Jobst's explanation as I was startled by
> it, too. It's hard to picture a flexible chain pushing the snap link
> together causing it to open. I don't have a good alternative theory.
>
> The notion that the snap link was just misintalled seems like a
> non-starter to me: either it would have been snapped into the locked
> position the first time it came under tension, in which case only the
> noise would have been noticed; or it would have been simply pulled
> >apart
Brandt wrote:
>>Try to imagine how unusual it is that the forward roller of the
>>PowerLink was positioned on the entry to the sprocket so that when
>>the chain skipped, the advancing length of following chain,
>>inertially pushed the chain forward against the relatively
>>immobile PowerLink while the chain line was just right to cause
>>the cover plate to be deflected inward enough to clear the locking
>>contour of the stepped release slot.
This all happened in milliseconds. Although the coverplate of the
PowerLink disengages, the pins would still be intact. One would
have to move the chain inward (take the chain out of tension) and
then move the chain outwards (the opposite direction of the chain pull)
to release the still pinned Powerlink. I just don't see how this could
happen by shifting down under tension in a matter of milliseconds.
http://www.hostelshoppe.com/images/products/la_sram_powerlink.jpg
> It would certainly be a freak occurrence.
Yes agree, it sure would be.
Don't get me wrong here, I do enjoy Brandt's post, I read most of them.
He's taught me quite a bit about bicycle maintenance, and I still practice
them today. I was concerned about the PowerLink because I use them.
I was riding him in humor about the Oliver Stone post, no harm.
-tom
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Date: 28 Jun 2007 16:28:52
From: Tim McNamara
Subject: Re: Safe to lengthen a chain?
|
In article <f60e7g$94p$1@news.Stanford.EDU >,
"Tom Nakashima" <tom@slac.stanford.edu > wrote:
> "Tim McNamara" <timmcn@bitstream.net> wrote in message
> news:timmcn-5B3CD4.18453527062007@news.iphouse.com...
> > In article <f5u9sr$r3v$1@news.Stanford.EDU>, "Tom Nakashima"
> > <tom@slac.stanford.edu> wrote:
> >
> >> > <jobst.brandt@stanfordalumni.org> wrote in message
> >> > news:4681b1b4$0$14130$742ec2ed@news.sonic.net...
> >> >>
> >> >> Try to imagine how unusual it is that the forward roller of the
> >> >> PowerLink was positioned on the entry to the sprocket so that
> >> >> when the chain skipped, the advancing length of following
> >> >> chain, inertially pushed the chain forward against the
> >> >> relatively immobile PowerLink while the chain line was just
> >> >> right to cause the cover plate to be deflected inward enough to
> >> >> clear the locking contour of the stepped release slot. I
> >> >> reported this because it was such an unusual mechanical
> >> >> coincidence of events but realized that no one understood or
> >> >> cared what occurred from the silence that followed.
> >> >>
> >> >> Jobst Brandt
> >> >
> >>
> >> That is one magic PowerLink Sorry I couldn't resist:
> >>
> >> The Magic Bullet Theory by Jim Garrison (Kevin Costner) from the
> >> Movie JFK:
> >>
> >> The magic bullet enters the President's back, headed downward at
> >> an angle of 17 degrees. It then moves upward in order to leave
> >> Kennedy's body from the front of his neck -- his neck wound number
> >> two -- where it waits 1.6 seconds, turns right and continues into
> >> Connally's body at the rear of his right armpit -- wound number
> >> three. Then, the bullet heads downward at an angle of 27 degrees,
> >> shattering Connally's fifth rib and leaving from the right side of
> >> his chest -- wounds four and five. The bullet continues downward
> >> and then enters Connally's right wrist -- wound number six --
> >> shattering the radius bone. It then enters his left thigh -- wound
> >> number seven -- from which it later falls out and is found in
> >> almost "pristine" condition on a stretcher in a corridor of
> >> Parkland Hospital.
> >>
> >> That is one magic bullet.
> >
> > What's "magical" is that you appear to think Oliver Stone's movie
> > was factual, if you're citing it in this context. Surely there is
> > a more reasonable argument than citing conspiracy theory fantasy.
>
> Actually I enjoyed Stone's myth but thought Jerry Seinfeld's theory
> of the magic loogie was factual.
It *was* sorta funny (I'm not a Seinfeld fan, though, just to put that
in context. Someone else might find it hilarious).
> > I understand the resistance to Jobst's explanation as I was
> > startled by it, too. It's hard to picture a flexible chain pushing
> > the snap link together causing it to open. I don't have a good
> > alternative theory.
> >
> > The notion that the snap link was just misintalled seems like a
> > non-starter to me: either it would have been snapped into the
> > locked position the first time it came under tension, in which case
> > only the noise would have been noticed; or it would have been
> > simply pulled
> > >apart
>
> Brandt wrote:
> >>Try to imagine how unusual it is that the forward roller of the
> >>PowerLink was positioned on the entry to the sprocket so that when
> >>the chain skipped, the advancing length of following chain,
> >>inertially pushed the chain forward against the relatively immobile
> >>PowerLink while the chain line was just right to cause the cover
> >>plate to be deflected inward enough to clear the locking contour of
> >>the stepped release slot.
>
> This all happened in milliseconds. Although the coverplate of the
> PowerLink disengages, the pins would still be intact. One would have
> to move the chain inward (take the chain out of tension) and then
> move the chain outwards (the opposite direction of the chain pull) to
> release the still pinned Powerlink. I just don't see how this could
> happen by shifting down under tension in a matter of milliseconds.
> http://www.hostelshoppe.com/images/products/la_sram_powerlink.jpg
If I understand Jobst's report correctly, he wasn't shifting gears. He
was climbing (which in his case is often a 47 x 13 kind of thing, from
what he's written in the past) and so pushing hard on the pedal. I
gather that the chain rode up the teeth of a worn 13T cog and then
skipped forward, snapping down into the next valley with an abrupt jolt.
There's lots of energy in those situations and the chain can get whipped
around pretty hard. Now, I might also be totally mis-imagining the
situation or might have missed something crucial in the 150 posts, since
I haven't read every single one.
> > It would certainly be a freak occurrence.
>
> Yes agree, it sure would be.
Yup. And happily so, eh?
> Don't get me wrong here, I do enjoy Brandt's post, I read most of
> them. He's taught me quite a bit about bicycle maintenance, and I
> still practice them today. I was concerned about the PowerLink
> because I use them. I was riding him in humor about the Oliver Stone
> post, no harm. -tom
I use whatever link comes with whatever chain I find on sale, but they
all seem to be the same basic design as the PowerLink rather than the
old master link which had the two pins attached to one side plate. I'm
not concerned given that this is the first report of something like this
in, what, at least 10 years of these things being in use?
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Date: 28 Jun 2007 16:50:10
From:
Subject: Re: Safe to lengthen a chain?
|
On Thu, 28 Jun 2007 16:28:52 -0500, Tim McNamara
<timmcn@bitstream.net > wrote:
[snip]
>If I understand Jobst's report correctly, he wasn't shifting gears. He
>was climbing (which in his case is often a 47 x 13 kind of thing, from
>what he's written in the past) and so pushing hard on the pedal. I
>gather that the chain rode up the teeth of a worn 13T cog and then
>skipped forward, snapping down into the next valley with an abrupt jolt.
>There's lots of energy in those situations and the chain can get whipped
>around pretty hard.
[snip]
Dear Tim,
There is a lot of energy (or force), but there's also a lot of mass
that may not be obvious.
It's not just the four links of chain between the idler pulley and the
13-tooth gear that must speed up and slow down.
It's the whole 100+ link chain wrapped around the two sprockets and
the two idler pulleys, plus the entire crank, plus both the rider's
legs that have to accelerate in half an inch of travel to a speed
great enough that the linear momentum of those four links is enough to
bang the quick-connect open.
When I was thinking of whacking a loose chain with a hammer and Jobst
was suggesting his more elegant idea of using a rubber band to fire a
few links of chain against a pipe, we may both have been forgetting
that our schemes involved an awful lot of speed that may not be
possible in the real situation.
Just to illustrate how the mass and acceleration and speed get tricky,
here's a _bad_ example that I chased down.
Imagine a bicycle propped up and standing still, with a rider standing
on one foot on the leading pedal of a horizontal 175 mm crank with a
53-tooth sprocket.
Obviously, his whole weight is pushing down on the pedal and putting a
huge strain on the chain.
Imagine the tremendous speed with which the chain will slam into the
next tooth if it skips!
It may be less than 1.43 mph. (Calculations to follow.)
We tend to confuse the impressive force (the rider's whole weight!)
with the acceleration.
For a 175 mm crank, the pedal circle is 350 mm * 3.141 = 1100 mm.
When the half-inch chain skips one link, the pedal on which the rider
is standing acts like a hangman's trap and rotates 1/53 of the pedal
circle.
To simplify things, let's pretend that this small drop is straight
down, instead of slightly curved: 1100 mm / 53 = 20.775 mm.
Okay, I lied. I'm not going to calculate the speed of an object in
free fall for 20.775 mm. Luckily there's a very precise free fall
calculator that lets you stick a single value in, click, and get an
answer:
http://hyperphysics.phy-astr.gsu.edu/hbase/traj.html
For 0.020775 meters, the calculator predicts a free-fall speed of
2.0935512 feet per second.
Despite having Chalo standing on the pedal when it skips, the pedal
_may_ reach a speed of only 1.43 miles per hour. (Caveats follow.)
Meanwhile, back at the 13-tooth, the chain has moved only half an
inch, about 12.7 mm, less than the pedal--so it's going even slower.
The _leading_ link beyond the quick-connect might break the gear tooth
off because of its tremendous force.
But the short section of a couple of chain links _trailing_ behind the
quick connect will "slam" into the back of the decelerating
quick-connect link at less than 1.5 mph. You can develop far more
impact than this by flicking your fingernail against a quick-connect.
So why is this a bad example?
I see two potential problems.
First, what if there's a lot more force stored up spring-style in the
frame, crank, and taut chain? More force with the same mass would
produce a greater acceleration. If Chalo is teetering motionless on
the leading pedal of a bike standing still, the metal parts may be
stretched a lot more than the naive example expected.
Release a stretched rubber band, and you can get far more acceleration
than mere free-fall.
But I don't know how to calculate this effect theoretically or measure
it practically.
Second, the rider may can probably generate a _faster_ skip when he's
sitting instead of standing on the pedal.
The absolute speed is what matters, not the raw force. It's the ratio
of total mass to available force that determines acceleration and
impact speed in our half-inch sprint.
By sitting and using muscle instead of gravity, the rider can increase
the force and reduce the mass that must be accelerated. (He still has
to accelerate both his legs to some degree--remember, his rear leg has
to accelerate up just as much as his front leg accelerates down.)
A feeble rubber band can accelerate a four-inch chain section enough
in about three inches to fling it fifty feet--I tried it in my
driveway.
But it's the ratio of the rubber band's feeble force to the tiny mass
of the handful of chain links that makes this impressive acceleration
possible.
Use the same rubber band to try to spin a pedal and crank against the
chain and freewheel, and you get less than a quarter-turn of movement.
No human eye can tell how fast the pedal is moving in that first half
inch or so, but things are obviously flying only about a foot, roughly
two orders of magnitude less than fifty feet.
So I still don't know how to predict in theory or measure in practice
the speed with which a skipping chain decelerates as it slams into the
next position on the 13-tooth. And it's the speed that determines
whether the short section of chain between the idler pulley and the
13-tooth has enough force to bang the two halves of a quick-connect
link together and release them.
Cheers,
Carl Fogel
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| | | | | |
Date: 29 Jun 2007 06:42:13
From: Tom Nakashima
Subject: Re: Safe to lengthen a chain?
|
<carlfogel@comcast.net > wrote in message
news:77a883hb8e7sslso9435fs0j70a44feiom@4ax.com...
> On Thu, 28 Jun 2007 16:28:52 -0500, Tim McNamara
> <timmcn@bitstream.net> wrote:
>
> [snip]
>
>>If I understand Jobst's report correctly, he wasn't shifting gears. He
>>was climbing (which in his case is often a 47 x 13 kind of thing, from
>>what he's written in the past) and so pushing hard on the pedal. I
>>gather that the chain rode up the teeth of a worn 13T cog and then
>>skipped forward, snapping down into the next valley with an abrupt jolt.
>>There's lots of energy in those situations and the chain can get whipped
>>around pretty hard.
>
> [snip]
>
> Dear Tim,
>
> There is a lot of energy (or force), but there's also a lot of mass
> that may not be obvious.
>
> It's not just the four links of chain between the idler pulley and the
> 13-tooth gear that must speed up and slow down.
>
> It's the whole 100+ link chain wrapped around the two sprockets and
> the two idler pulleys, plus the entire crank, plus both the rider's
> legs that have to accelerate in half an inch of travel to a speed
> great enough that the linear momentum of those four links is enough to
> bang the quick-connect open.
>
> When I was thinking of whacking a loose chain with a hammer and Jobst
> was suggesting his more elegant idea of using a rubber band to fire a
> few links of chain against a pipe, we may both have been forgetting
> that our schemes involved an awful lot of speed that may not be
> possible in the real situation.
>
> Just to illustrate how the mass and acceleration and speed get tricky,
> here's a _bad_ example that I chased down.
>
> Imagine a bicycle propped up and standing still, with a rider standing
> on one foot on the leading pedal of a horizontal 175 mm crank with a
> 53-tooth sprocket.
>
> Obviously, his whole weight is pushing down on the pedal and putting a
> huge strain on the chain.
>
> Imagine the tremendous speed with which the chain will slam into the
> next tooth if it skips!
>
> It may be less than 1.43 mph. (Calculations to follow.)
>
> We tend to confuse the impressive force (the rider's whole weight!)
> with the acceleration.
>
> For a 175 mm crank, the pedal circle is 350 mm * 3.141 = 1100 mm.
>
> When the half-inch chain skips one link, the pedal on which the rider
> is standing acts like a hangman's trap and rotates 1/53 of the pedal
> circle.
>
> To simplify things, let's pretend that this small drop is straight
> down, instead of slightly curved: 1100 mm / 53 = 20.775 mm.
>
> Okay, I lied. I'm not going to calculate the speed of an object in
> free fall for 20.775 mm. Luckily there's a very precise free fall
> calculator that lets you stick a single value in, click, and get an
> answer:
>
> http://hyperphysics.phy-astr.gsu.edu/hbase/traj.html
>
> For 0.020775 meters, the calculator predicts a free-fall speed of
> 2.0935512 feet per second.
>
> Despite having Chalo standing on the pedal when it skips, the pedal
> _may_ reach a speed of only 1.43 miles per hour. (Caveats follow.)
>
> Meanwhile, back at the 13-tooth, the chain has moved only half an
> inch, about 12.7 mm, less than the pedal--so it's going even slower.
>
> The _leading_ link beyond the quick-connect might break the gear tooth
> off because of its tremendous force.
>
> But the short section of a couple of chain links _trailing_ behind the
> quick connect will "slam" into the back of the decelerating
> quick-connect link at less than 1.5 mph. You can develop far more
> impact than this by flicking your fingernail against a quick-connect.
>
> So why is this a bad example?
>
> I see two potential problems.
>
> First, what if there's a lot more force stored up spring-style in the
> frame, crank, and taut chain? More force with the same mass would
> produce a greater acceleration. If Chalo is teetering motionless on
> the leading pedal of a bike standing still, the metal parts may be
> stretched a lot more than the naive example expected.
>
> Release a stretched rubber band, and you can get far more acceleration
> than mere free-fall.
>
> But I don't know how to calculate this effect theoretically or measure
> it practically.
>
> Second, the rider may can probably generate a _faster_ skip when he's
> sitting instead of standing on the pedal.
>
> The absolute speed is what matters, not the raw force. It's the ratio
> of total mass to available force that determines acceleration and
> impact speed in our half-inch sprint.
>
> By sitting and using muscle instead of gravity, the rider can increase
> the force and reduce the mass that must be accelerated. (He still has
> to accelerate both his legs to some degree--remember, his rear leg has
> to accelerate up just as much as his front leg accelerates down.)
>
> A feeble rubber band can accelerate a four-inch chain section enough
> in about three inches to fling it fifty feet--I tried it in my
> driveway.
>
> But it's the ratio of the rubber band's feeble force to the tiny mass
> of the handful of chain links that makes this impressive acceleration
> possible.
>
> Use the same rubber band to try to spin a pedal and crank against the
> chain and freewheel, and you get less than a quarter-turn of movement.
> No human eye can tell how fast the pedal is moving in that first half
> inch or so, but things are obviously flying only about a foot, roughly
> two orders of magnitude less than fifty feet.
>
> So I still don't know how to predict in theory or measure in practice
> the speed with which a skipping chain decelerates as it slams into the
> next position on the 13-tooth. And it's the speed that determines
> whether the short section of chain between the idler pulley and the
> 13-tooth has enough force to bang the two halves of a quick-connect
> link together and release them.
>
> Cheers,
>
> Carl Fogel
Carl, maybe it's not the force that separated the quick-connect link?
Climbing in a 47/13 (not sure how steep the climb was) on steep climbs
a cyclist sometimes squares his pedals, meaning not a smooth rotation
of the pedals, but hesitates. This hesitation causes backlash (slack) in
the chain. If the quick-connect wasn't installed properly (didn't
lock in) it's possible for the side plate to disengage. I'm not saying
Jobst didn't install the quick-connect properly. I can recall I had once not
heard a clicking sound of the sideplates engaging into the grooves when I
installed a PowerLink. When I checked it on a bike stand, it easily came
apart. There's a groove that the side plate has to engage into, sometimes
the plate has a hard time finding it's way into that groove.
http://www.hostelshoppe.com/images/products/la_sram_powerlink.jpg
-tom
|
| | | | | | |
Date: 29 Jun 2007 12:49:40
From:
Subject: Re: Safe to lengthen a chain?
|
On Fri, 29 Jun 2007 06:42:13 -0700, "Tom Nakashima"
<tom@slac.stanford.edu > wrote:
>
><carlfogel@comcast.net> wrote in message
>news:77a883hb8e7sslso9435fs0j70a44feiom@4ax.com...
>> On Thu, 28 Jun 2007 16:28:52 -0500, Tim McNamara
>> <timmcn@bitstream.net> wrote:
>>
>> [snip]
>>
>>>If I understand Jobst's report correctly, he wasn't shifting gears. He
>>>was climbing (which in his case is often a 47 x 13 kind of thing, from
>>>what he's written in the past) and so pushing hard on the pedal. I
>>>gather that the chain rode up the teeth of a worn 13T cog and then
>>>skipped forward, snapping down into the next valley with an abrupt jolt.
>>>There's lots of energy in those situations and the chain can get whipped
>>>around pretty hard.
>>
>> [snip]
>>
>> Dear Tim,
>>
>> There is a lot of energy (or force), but there's also a lot of mass
>> that may not be obvious.
>>
>> It's not just the four links of chain between the idler pulley and the
>> 13-tooth gear that must speed up and slow down.
>>
>> It's the whole 100+ link chain wrapped around the two sprockets and
>> the two idler pulleys, plus the entire crank, plus both the rider's
>> legs that have to accelerate in half an inch of travel to a speed
>> great enough that the linear momentum of those four links is enough to
>> bang the quick-connect open.
>>
>> When I was thinking of whacking a loose chain with a hammer and Jobst
>> was suggesting his more elegant idea of using a rubber band to fire a
>> few links of chain against a pipe, we may both have been forgetting
>> that our schemes involved an awful lot of speed that may not be
>> possible in the real situation.
>>
>> Just to illustrate how the mass and acceleration and speed get tricky,
>> here's a _bad_ example that I chased down.
>>
>> Imagine a bicycle propped up and standing still, with a rider standing
>> on one foot on the leading pedal of a horizontal 175 mm crank with a
>> 53-tooth sprocket.
>>
>> Obviously, his whole weight is pushing down on the pedal and putting a
>> huge strain on the chain.
>>
>> Imagine the tremendous speed with which the chain will slam into the
>> next tooth if it skips!
>>
>> It may be less than 1.43 mph. (Calculations to follow.)
>>
>> We tend to confuse the impressive force (the rider's whole weight!)
>> with the acceleration.
>>
>> For a 175 mm crank, the pedal circle is 350 mm * 3.141 = 1100 mm.
>>
>> When the half-inch chain skips one link, the pedal on which the rider
>> is standing acts like a hangman's trap and rotates 1/53 of the pedal
>> circle.
>>
>> To simplify things, let's pretend that this small drop is straight
>> down, instead of slightly curved: 1100 mm / 53 = 20.775 mm.
>>
>> Okay, I lied. I'm not going to calculate the speed of an object in
>> free fall for 20.775 mm. Luckily there's a very precise free fall
>> calculator that lets you stick a single value in, click, and get an
>> answer:
>>
>> http://hyperphysics.phy-astr.gsu.edu/hbase/traj.html
>>
>> For 0.020775 meters, the calculator predicts a free-fall speed of
>> 2.0935512 feet per second.
>>
>> Despite having Chalo standing on the pedal when it skips, the pedal
>> _may_ reach a speed of only 1.43 miles per hour. (Caveats follow.)
>>
>> Meanwhile, back at the 13-tooth, the chain has moved only half an
>> inch, about 12.7 mm, less than the pedal--so it's going even slower.
>>
>> The _leading_ link beyond the quick-connect might break the gear tooth
>> off because of its tremendous force.
>>
>> But the short section of a couple of chain links _trailing_ behind the
>> quick connect will "slam" into the back of the decelerating
>> quick-connect link at less than 1.5 mph. You can develop far more
>> impact than this by flicking your fingernail against a quick-connect.
>>
>> So why is this a bad example?
>>
>> I see two potential problems.
>>
>> First, what if there's a lot more force stored up spring-style in the
>> frame, crank, and taut chain? More force with the same mass would
>> produce a greater acceleration. If Chalo is teetering motionless on
>> the leading pedal of a bike standing still, the metal parts may be
>> stretched a lot more than the naive example expected.
>>
>> Release a stretched rubber band, and you can get far more acceleration
>> than mere free-fall.
>>
>> But I don't know how to calculate this effect theoretically or measure
>> it practically.
>>
>> Second, the rider may can probably generate a _faster_ skip when he's
>> sitting instead of standing on the pedal.
>>
>> The absolute speed is what matters, not the raw force. It's the ratio
>> of total mass to available force that determines acceleration and
>> impact speed in our half-inch sprint.
>>
>> By sitting and using muscle instead of gravity, the rider can increase
>> the force and reduce the mass that must be accelerated. (He still has
>> to accelerate both his legs to some degree--remember, his rear leg has
>> to accelerate up just as much as his front leg accelerates down.)
>>
>> A feeble rubber band can accelerate a four-inch chain section enough
>> in about three inches to fling it fifty feet--I tried it in my
>> driveway.
>>
>> But it's the ratio of the rubber band's feeble force to the tiny mass
>> of the handful of chain links that makes this impressive acceleration
>> possible.
>>
>> Use the same rubber band to try to spin a pedal and crank against the
>> chain and freewheel, and you get less than a quarter-turn of movement.
>> No human eye can tell how fast the pedal is moving in that first half
>> inch or so, but things are obviously flying only about a foot, roughly
>> two orders of magnitude less than fifty feet.
>>
>> So I still don't know how to predict in theory or measure in practice
>> the speed with which a skipping chain decelerates as it slams into the
>> next position on the 13-tooth. And it's the speed that determines
>> whether the short section of chain between the idler pulley and the
>> 13-tooth has enough force to bang the two halves of a quick-connect
>> link together and release them.
>>
>> Cheers,
>>
>> Carl Fogel
>
>Carl, maybe it's not the force that separated the quick-connect link?
>Climbing in a 47/13 (not sure how steep the climb was) on steep climbs
>a cyclist sometimes squares his pedals, meaning not a smooth rotation
>of the pedals, but hesitates. This hesitation causes backlash (slack) in
>the chain. If the quick-connect wasn't installed properly (didn't
>lock in) it's possible for the side plate to disengage. I'm not saying
>Jobst didn't install the quick-connect properly. I can recall I had once not
>heard a clicking sound of the sideplates engaging into the grooves when I
>installed a PowerLink. When I checked it on a bike stand, it easily came
>apart. There's a groove that the side plate has to engage into, sometimes
>the plate has a hard time finding it's way into that groove.
>http://www.hostelshoppe.com/images/products/la_sram_powerlink.jpg
>-tom
Dear Tom,
You've come up with another possibility for a quick-connect
separating.
If a rider suffers a chain skip at just the wrong moment near the
bottom of the pedal cycle, he might get a back-lash, wave, flip, or
whatever it's called. If this causes the double arm of the derailleur
to go boing! and the quick-connect in just the right spot, the motion
might compress the two half-links enough for them to separate.
That suggests an even more dramatic possibility. The Z-bend in the
derailleur doesn't always handle bouncing very well. A chain skip
coupled with a bump in the road might bounce a chain enough to get
cross-wise with the idler pulleys or gear cluster and jam. If the
quick-connect is in just the right spot, it might come apart when a
chain jams, whereupon the chain falls off and leaves no sign of the
jam.
Whatever happened seems to be an extremely rare event. I'm interested
in Jobst's explanation, partly because it leads to so many curious
details and partly because it leads to so many dogmatic claims that
lead to more curious details. If Jobst's theory is correct, it should
be able to withstand some questions. If not, it still raises
interesting questions. And whether he's right or wrong, he deserves
credit for posting a plausible explanation--look how much fun you and
I are having wondering about how a quick-connect might come apart.
Cheers,
Carl Fogel
|
| | | | | | | |
Date: 29 Jun 2007 19:57:11
From:
Subject: Re: Safe to lengthen a chain?
|
Carl Fogel writes:
>> Carl, maybe it's not the force that separated the quick-connect
>> link? Climbing in a 47/13 (not sure how steep the climb was) on
>> steep climbs a cyclist sometimes squares his pedals, meaning not a
>> smooth rotation of the pedals, but hesitates. This hesitation
>> causes backlash (slack) in the chain. If the quick-connect wasn't
>> installed properly (didn't lock in) it's possible for the side
>> plate to disengage. I'm not saying Jobst didn't install the
>> quick-connect properly. I can recall I had once not heard a
>> clicking sound of the side plates engaging into the grooves when I
>> installed a PowerLink. When I checked it on a bike stand, it
>> easily came apart. There's a groove that the side plate has to
>> engage into, sometimes the plate has a hard time finding it's way
>> into that groove.
>> http://www.hostelshoppe.com/images/products/la_sram_powerlink.jpg
> You've come up with another possibility for a quick-connect
> separating.
> If a rider suffers a chain skip at just the wrong moment near the
> bottom of the pedal cycle, he might get a back-lash, wave, flip, or
> whatever it's called. If this causes the double arm of the
> derailleur to go boing! and the quick-connect in just the right
> spot, the motion might compress the two half-links enough for them
> to separate.
> That suggests an even more dramatic possibility. The Z-bend in the
> derailleur doesn't always handle bouncing very well. A chain skip
> coupled with a bump in the road might bounce a chain enough to get
> cross-wise with the idler pulleys or gear cluster and jam. If the
> quick-connect is in just the right spot, it might come apart when a
> chain jams, whereupon the chain falls off and leaves no sign of the
> jam.
As I said, you apparently have not experienced chain skip on worn
sprockets, especially one that barely skips and requires high chain
tension to do so. You may recall that I said it skipped only once in
awhile and that I had ridden that gear for a few miles before the
grade where it skipped. The scenario you seem to like doesn't occur
with such a chain and sprocket combination because it requires strong
pedaling.
> Whatever happened seems to be an extremely rare event. I'm
> interested in Jobst's explanation, partly because it leads to so
> many curious details and partly because it leads to so many dogmatic
> claims that lead to more curious details. If Jobst's theory is
> correct, it should be able to withstand some questions. If not, it
> still raises interesting questions. And whether he's right or
> wrong, he deserves credit for posting a plausible explanation--look
> how much fun you and I are having wondering about how a
> quick-connect might come apart.
We aren't getting anywhere. This is becoming a deja-vu experience
with all sorts of specious scenarios, all contrary to the concise
explanation I gave of what occurred.
Jobst Brandt
|
| | | | | | | | |
Date: 29 Jun 2007 23:28:39
From: Sandy
Subject: Re: Safe to lengthen a chain?
|
Dans le message de news:46856417$0$14069$742ec2ed@news.sonic.net,
jobst.brandt@stanfordalumni.org <jobst.brandt@stanfordalumni.org > a
réfléchi, et puis a déclaré :
> We aren't getting anywhere. This is becoming a deja-vu experience
> with all sorts of specious scenarios, all contrary to the concise
> explanation I gave of what occurred.
>
> Jobst Brandt
When are you going to post the smiley?
|
| | | | | | | | |
Date: 29 Jun 2007 14:16:04
From:
Subject: Re: Safe to lengthen a chain?
|
On 29 Jun 2007 19:57:11 GMT, jobst.brandt@stanfordalumni.org wrote:
[snip]
>As I said, you apparently have not experienced chain skip on worn
>sprockets, especially one that barely skips and requires high chain
>tension to do so.
[snip]
Dear Jobst,
Comments like that are what make me skeptical of so much else that you
say.
I've been skipping 52x12 and 53x11 chains several times a year for
over twenty years.
Those are the gears that I use for most of daily ride, and they're
higher than your 47-tooth setup.
All too often I wait until my chain starts skipping to replace my
worn-out high gear.
I was delighted when I switched from a 52 and soft 12-tooth Sachs-Aris
freewheel cogs, which began to skip every three months, to a 53 and
much harder Shimano 11-tooth cogs, which often last five or six
months, despite fewer rear teeth, higher chain tension, and a tighter
sprocket circle.
Cheers,
Carl Fogel
|
| | | | | | | | | |
Date: 29 Jun 2007 20:33:10
From:
Subject: Re: Safe to lengthen a chain?
|
Carl Fogel writes:
>> As I said, you apparently have not experienced chain skip on worn
>> sprockets, especially one that barely skips and requires high chain
>> tension to do so.
> [snip]
> Comments like that are what make me skeptical of so much else that
> you say.
How else can you explain the reinterpretation of the event to picture
things that cannot occur. Either you are working at misinterpreting
what I wrote or you don't understand the phenomenon. Take your pick.
If you review the exchange, new scenarios that have little to do with
the event are offered with each turn. I'm not sure what the
motivation is but it is trying.
> I've been skipping 52x12 and 53x11 chains several times a year for
> over twenty years.
Well! Why is the event that caused the link to separate so illusive?
> Those are the gears that I use for most of daily ride, and they're
> higher than your 47-tooth setup.
I rarely use the 47t sprocket, and not for the event in question.
> All too often I wait until my chain starts skipping to replace my
> worn-out high gear.
Chains don't "start" skipping, they skip when installed on worn
sprockets and that is the appropriate time to get new ones, not
before, because the sprocket has no effect on chain life. Chain life
under normal circumstances is dependent on pin-in-sleeve wear, known
as pitch elongation.
> I was delighted when I switched from a 52 and soft 12-tooth
> Sachs-Aris freewheel cogs, which began to skip every three months,
> to a 53 and much harder Shimano 11-tooth cogs, which often last five
> or six months, despite fewer rear teeth, higher chain tension, and a
> tighter sprocket circle.
I don't see what the 52t chainwheel has to do with this. Chainwheels
(driving sprockets) do not skip. Driven sprockets do.
I think we are drifting.
Jobst Brandt
|
| | | | | | | | | | |
Date: 30 Jun 2007 00:32:17
From:
Subject: Re: Safe to lengthen a chain?
|
On 29 Jun 2007 20:33:10 GMT, jobst.brandt@stanfordalumni.org wrote:
>Carl Fogel writes:
>
>>> As I said, you apparently have not experienced chain skip on worn
>>> sprockets, especially one that barely skips and requires high chain
>>> tension to do so.
>
>> [snip]
>
>> Comments like that are what make me skeptical of so much else that
>> you say.
>
>How else can you explain the reinterpretation of the event to picture
>things that cannot occur. Either you are working at misinterpreting
>what I wrote or you don't understand the phenomenon. Take your pick.
>If you review the exchange, new scenarios that have little to do with
>the event are offered with each turn. I'm not sure what the
>motivation is but it is trying.
>
>> I've been skipping 52x12 and 53x11 chains several times a year for
>> over twenty years.
>
>Well! Why is the event that caused the link to separate so illusive?
>
>> Those are the gears that I use for most of daily ride, and they're
>> higher than your 47-tooth setup.
>
>I rarely use the 47t sprocket, and not for the event in question.
>
>> All too often I wait until my chain starts skipping to replace my
>> worn-out high gear.
>
>Chains don't "start" skipping, they skip when installed on worn
>sprockets and that is the appropriate time to get new ones, not
>before, because the sprocket has no effect on chain life. Chain life
>under normal circumstances is dependent on pin-in-sleeve wear, known
>as pitch elongation.
>
>> I was delighted when I switched from a 52 and soft 12-tooth
>> Sachs-Aris freewheel cogs, which began to skip every three months,
>> to a 53 and much harder Shimano 11-tooth cogs, which often last five
>> or six months, despite fewer rear teeth, higher chain tension, and a
>> tighter sprocket circle.
>
>I don't see what the 52t chainwheel has to do with this. Chainwheels
>(driving sprockets) do not skip. Driven sprockets do.
>
>I think we are drifting.
>
>Jobst Brandt
Dear Jobst,
Gosh, this looks familiar!
Someone questions one of your claims.
You issue your standard announcement that he must not have ever [fill
in the blank].
He points out that he has actually has considerable experience in it.
(In this case, I use higher gearing than you do, contrary to your
silly shoot-from-the-hip claim that I don't, and it sounds as if I
suffer more chain skipping than you, also contrary to your claim that
I haven't experienced it.)
You disappear in a puff of smoke about how the topic is drifting and
hope that no one remembers this the next time that you insist that
your claims are not to be questioned.
Cheers,
Carl Fogel
|
| | | | | | | | | | | |
Date: 30 Jun 2007 10:12:33
From: Sandy
Subject: Re: Safe to lengthen a chain?
|
Dans le message de news:bntb83p5c3qpd89aurns4j0qtlg17onjq3@4ax.com,
carlfogel@comcast.net <carlfogel@comcast.net > a réfléchi, et puis a déclaré
:
> On 29 Jun 2007 20:33:10 GMT, jobst.brandt@stanfordalumni.org wrote:
>
>> Carl Fogel writes:
>>
>>>> As I said, you apparently have not experienced chain skip on worn
>>>> sprockets, especially one that barely skips and requires high chain
>>>> tension to do so.
>>
>>> [snip]
>>
>>> Comments like that are what make me skeptical of so much else that
>>> you say.
>>
>> How else can you explain the reinterpretation of the event to picture
>> things that cannot occur. Either you are working at misinterpreting
>> what I wrote or you don't understand the phenomenon. Take your pick.
>> If you review the exchange, new scenarios that have little to do with
>> the event are offered with each turn. I'm not sure what the
>> motivation is but it is trying.
>>
>>> I've been skipping 52x12 and 53x11 chains several times a year for
>>> over twenty years.
>>
>> Well! Why is the event that caused the link to separate so illusive?
>>
>>> Those are the gears that I use for most of daily ride, and they're
>>> higher than your 47-tooth setup.
>>
>> I rarely use the 47t sprocket, and not for the event in question.
>>
>>> All too often I wait until my chain starts skipping to replace my
>>> worn-out high gear.
>>
>> Chains don't "start" skipping, they skip when installed on worn
>> sprockets and that is the appropriate time to get new ones, not
>> before, because the sprocket has no effect on chain life. Chain life
>> under normal circumstances is dependent on pin-in-sleeve wear, known
>> as pitch elongation.
>>
>>> I was delighted when I switched from a 52 and soft 12-tooth
>>> Sachs-Aris freewheel cogs, which began to skip every three months,
>>> to a 53 and much harder Shimano 11-tooth cogs, which often last five
>>> or six months, despite fewer rear teeth, higher chain tension, and a
>>> tighter sprocket circle.
>>
>> I don't see what the 52t chainwheel has to do with this. Chainwheels
>> (driving sprockets) do not skip. Driven sprockets do.
>>
>> I think we are drifting.
>>
>> Jobst Brandt
>
> Dear Jobst,
>
> Gosh, this looks familiar!
>
> Someone questions one of your claims.
>
> You issue your standard announcement that he must not have ever [fill
> in the blank].
>
> He points out that he has actually has considerable experience in it.
>
> (In this case, I use higher gearing than you do, contrary to your
> silly shoot-from-the-hip claim that I don't, and it sounds as if I
> suffer more chain skipping than you, also contrary to your claim that
> I haven't experienced it.)
>
> You disappear in a puff of smoke about how the topic is drifting and
> hope that no one remembers this the next time that you insist that
> your claims are not to be questioned.
>
> Cheers,
>
> Carl Fogel
An interesting observatopn. I always wondered what happened to his comments
on :
rims manufactured in this century -
tubular tires manufactured in this century -
tubular glue manufactured in this century -
clincher tires manufactured in this century -
cranksets manufactured in this century -
common chainring combinations -
7, 8, 9 and 10 speed drivetrains -
... since they don't arise from his personal experience.
Of course, there must be some experience amongst his "friends." Yes,
friends, a rather illusive [sic myself] club. Not to mention the Alps.
Yes, his personal reserve of downhills, where by sheer force of atmospheric
friction, his hair disappeared abruptly, shocked out of existence, sensing
the vaporization of Tubasti by overheated single-pivot brakes. Not Deltas,
of course, as any moron can see the total failure of that design without
opening the clamshell. Praise be (to something, maybe the original
collection of prime matter) that goatheads don't grow on alpine slopes.
Not content that his persona which we are familiar with evangelized right
thinking, his urge to teach led to developing an invisible doppelganger of
sorts. Big JB and little jb. Tell me if you have ever seen the two of them
in one place at the same time - no, of course not. While the evil sidekick
guzzled his corn liquor and spouted blasphemy (atheists must have some
parallel word), big JB never seems to have been able to make a frontal
attack on little jb, leaving his acolytes (atheists could probably use this
word) to knock down his personal strawman. Little jb happily rides the same
roads with his gleaming box-delivered, laid-back (not overstressed thus
needing no relief, so to speak) Mavic wheels, while big JB reflects on how
wonderful the 60's and 70's were, as though he still inhabited that era. Or
maybe he still does - where DO all those NOS products come from, anyway ?
It would be rude to write without recommending The Bicycle Wheel for your
bookshelf. It handily fits the need to even out warped flooring, when not
in constant use by the author himself to keep his ancient wheels spinning
smoothly. Those wheels with the same hubs, spokes, rims, tires and tubes
(occasionally filled with water or bourbon), except for the infrequently
necessary replacement parts. The book, the bible for wheel builders
everywhere. The book which, if used properly by everyone on two wheels,
will put Peter Chisholm out of business in a year. So let's get a plug in
for The Bicycle Wheel by Jobst Brandt. Did I mention The Bicycle Wheel by
Jobst Brandt ?
At dusk, when you see a bright day-glow bike approaching, hie thee away.
No, it's not the boogeyman. Or maybe it is. Justin boogeyman. Multiple
personality Justin boogeyman. To coexist in cacophony - Jb, with JB and
jb. There's room for one more. Who will be jB ? A Texan, no doubt,
running cyclists off the road with his Hummer. Big into petroleum. Wives,
lovers, kids, too. This could turn into a TV series. Black and white and
shades of grey. OK, not lovers. Sorry.
Must go. Got to get out and ride bike. Please excuse the grammar, there.
Repeated misuse or misstatement is often taken for the correct form or idea.
Turns into myth and lore. Sometimes, this effect has been called the Big
Lie.
Ciao, JB and jb and Jb and jB. See you in the Pyrénées.
--
Sandy
-
"Our knowledge is a little island in a great ocean of non-knowledge."
- Edward O. Wilson
|
| | | | | | | | | | |
Date: 29 Jun 2007 15:49:59
From: Bill Sornson
Subject: Re: Safe to lengthen a chain?
|
jobst.brandt@stanfordalumni.org wrote:
> Chainwheels
> (driving sprockets) do not skip. Driven sprockets do.
Ah, an old classic of yours. Try riding mountain bikes and say that
chainwheels don't skip. I have a full XTR crankset that I can't use because
of ring wear. Chains skip like crazy on it (small and middle rings for
sure; probably not the big ring)...
> I think we are drifting.
I think you are mistaken.
|
| | | | | | | | | | | |
Date: 30 Jun 2007 03:13:04
From:
Subject: Re: Safe to lengthen a chain?
|
Bill Sornson writes:
>> Chainwheels (driving sprockets) do not skip. Driven sprockets do.
> Ah, an old classic of yours. Try riding mountain bikes and say that
> chainwheels don't skip. I have a full XTR crankset that I can't use
> because of ring wear. Chains skip like crazy on it (small and
> middle rings for sure; probably not the big ring)...
I'd like to see those CW's. They probably have no teeth and then you
expect a wavy disk to work as a CW. I didn't say CW with only nubbins
of teeth won't skip. Actually they don't, they slip, there being no
digital arrest after each loss of drive.
Jobst Brandt
|
| | | | | | | | | | | |
Date: 30 Jun 2007 03:08:50
From:
Subject: Re: Safe to lengthen a chain?
|
Bill Sornson writes:
>> Chainwheels (driving sprockets) do not skip. Driven sprockets do.
> Ah, an old classic of yours. Try riding mountain bikes and say that
> chainwheels don't skip. I have a full XTR crankset that I can't use
> because of ring wear. Chains skip like crazy on it (small and
> middle rings for sure; probably not the big ring)...
I'd like to see those CW's. They probably have no teeth and then you
expect a wavy disk to work as a CW. I didn't say CW with only nubbins
of teeth won't skip. Actually they don't, the slip, there being no
digital arrest after each loss of drive.
Jobst Brandt
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Date: 29 Jun 2007 20:29:16
From: Bill Sornson
Subject: Re: Safe to lengthen a chain?
|
jobst.brandt@stanfordalumni.org wrote:
> Bill Sornson writes:
>> JB claimed: {missing attribution}
>>> Chainwheels (driving sprockets) do not skip. Driven sprockets do.
>> Ah, an old classic of yours. Try riding mountain bikes and say that
>> chainwheels don't skip. I have a full XTR crankset that I can't use
>> because of ring wear. Chains skip like crazy on it (small and
>> middle rings for sure; probably not the big ring)...
> I'd like to see those CW's. They probably have no teeth and then you
> expect a wavy disk to work as a CW. I didn't say CW with only nubbins
> of teeth won't skip. Actually they don't, the slip, there being no
> digital arrest after each loss of drive.
The crankset looks perfectly normal, and in fact worked fine with the old,
badly worn chain. (As did the cassette.)
As I recall, the chain finally broke, and when I replaced it I got horrible
skipping. I assumed it was the cogs, so I replaced the cassette. Still
skipped -- mostly middle ring but little did, too.
This conforms to the experience I (and countless others) have had with
RaceFace, TruVativ, and other name-brand mtb chain rings: it's why they
sell replacement rings! (Affordable, too, BTW, unlike my dusty XTR, for
which a middle ring runs roughly 70 bucks.)
I remember you making this silly claim a few years ago, and I spoke up then,
too. Ask any mountain biker if they've worn out chain rings and they will
answer YES! It's not only common, it's inevitable (assuming heavy use in
dirty conditions).
Now I admit that I haven't seen this occur with my ROAD chain rings, but
then again I live in San Diego so seldom encounter rain or other "grinding
paste" conditions.
To sum up, chain rings can and do wear to the point of chain skip. Period.
BS (not)
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Date: 29 Jun 2007 21:24:22
From: Bill Bushnell
Subject: Re: Safe to lengthen a chain?
|
In article <4685ce10$0$30617$4c368faf@roadrunner.com >,
"Bill Sornson" <askme@ask.me > wrote:
> jobst.brandt@stanfordalumni.org wrote:
> > I'd like to see those CW's. They probably have no teeth and then you
> > expect a wavy disk to work as a CW. I didn't say CW with only nubbins
> > of teeth won't skip. Actually they don't, the slip, there being no
> > digital arrest after each loss of drive.
> I remember you making this silly claim a few years ago, and I spoke up then,
> too. Ask any mountain biker if they've worn out chain rings and they will
> answer YES! It's not only common, it's inevitable (assuming heavy use in
> dirty conditions).
>
> Now I admit that I haven't seen this occur with my ROAD chain rings, but
> then again I live in San Diego so seldom encounter rain or other "grinding
> paste" conditions.
I had a 46t chainwheel with teeth worn to the point of slipping. This
was on a bike that spent most of its time on pavement but saw some time
on dirt roads. The teeth weren't wavey nubbins, but they were lightly
scalloped and topped slightly from wear.
The problem presented itself unexpectedly at an inopportune moment as I
was leaving the start line of an individual time trial, where I did a
standing start for the first hundred yards or so, something that I did
not frequently do. At the time I thought it was the rear sprocket, but
I later confirmed it was the chain slipping over the chainwheel teeth.
I wish I had saved that ring for my gallery, but I tossed it into the
recycling bin long ago.
--
Bill Bushnell
http://pobox.com/~bushnell/
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Date: 29 Jun 2007 21:34:59
From: Bill Sornson
Subject: Re: Safe to lengthen a chain?
|
Bill Bushnell wrote:
> In article <4685ce10$0$30617$4c368faf@roadrunner.com>,
> "Bill Sornson" <askme@ask.me> wrote:
>
>> jobst.brandt@stanfordalumni.org wrote:
>>> I'd like to see those CW's. They probably have no teeth and then
>>> you expect a wavy disk to work as a CW. I didn't say CW with only
>>> nubbins of teeth won't skip. Actually they don't, the slip, there
>>> being no digital arrest after each loss of drive.
>
>> I remember you making this silly claim a few years ago, and I spoke
>> up then, too. Ask any mountain biker if they've worn out chain
>> rings and they will answer YES! It's not only common, it's
>> inevitable (assuming heavy use in dirty conditions).
>>
>> Now I admit that I haven't seen this occur with my ROAD chain rings,
>> but then again I live in San Diego so seldom encounter rain or other
>> "grinding paste" conditions.
>
> I had a 46t chainwheel with teeth worn to the point of slipping. This
> was on a bike that spent most of its time on pavement but saw some
> time on dirt roads. The teeth weren't wavey nubbins, but they were
> lightly scalloped and topped slightly from wear.
>
> The problem presented itself unexpectedly at an inopportune moment as
> I was leaving the start line of an individual time trial, where I did
> a standing start for the first hundred yards or so, something that I
> did not frequently do. At the time I thought it was the rear
> sprocket, but I later confirmed it was the chain slipping over the
> chainwheel teeth.
>
> I wish I had saved that ring for my gallery, but I tossed it into the
> recycling bin long ago.
Yup, that's usually how you find out! REALLY cranking.
Thanks for the confirmation. (And note it was a pretty big ring, too.)
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Date: 30 Jun 2007 03:44:00
From:
Subject: Re: Safe to lengthen a chain?
|
Bill Sornson writes:
>>>> Chainwheels (driving sprockets) do not skip. Driven sprockets
do.
>>> Ah, an old classic of yours. Try riding mountain bikes and say
>>> that chainwheels don't skip. I have a full XTR crankset that I
>>> can't use because of ring wear. Chains skip like crazy on it
>>> (small and middle rings for sure; probably not the big ring)...
>> I'd like to see those CW's. They probably have no teeth and then
>> you expect a wavy disk to work as a CW. I didn't say CW with only
>> nubbins of teeth won't skip. Actually they don't, the slip, there
>> being no digital arrest after each loss of drive.
> The crankset looks perfectly normal, and in fact worked fine with
> the old, badly worn chain. (As did the cassette.)
> As I recall, the chain finally broke, and when I replaced it I got
> horrible skipping. I assumed it was the cogs, so I replaced the
> cassette. Still skipped -- mostly middle ring but little did, too.
> This conforms to the experience I (and countless others) have had
> with RaceFace, TruVativ, and other name-brand mtb chain rings: it's
> why they sell replacement rings! (Affordable, too, BTW, unlike my
> dusty XTR, for which a middle ring runs roughly 70 bucks.)
> I remember you making this silly claim a few years ago, and I spoke
> up then, too. Ask any mountain biker if they've worn out chain
> rings and they will answer YES! It's not only common, it's
> inevitable (assuming heavy use in dirty conditions).
> Now I admit that I haven't seen this occur with my ROAD chain rings,
> but then again I live in San Diego so seldom encounter rain or other
> "grinding paste" conditions.
> To sum up, chain rings can and do wear to the point of chain skip.
Period.
Well I posted a picture of a 47t chainwheel that had full height teeth
that were paper thin and served well with new chains as did all of
those of my riding pals who rode thier CW to death. I'll have to
assume that this is not the way smaller CW behave, possibly because
there being too few teeth engaged. I'm curious about the size of
these CW's.
Jobst Brandt
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Date: 30 Jun 2007 15:19:00
From: A Muzi
Subject: Re: Safe to lengthen a chain?
|
jobst.brandt@stanfordalumni.org wrote:
>>>>> Chainwheels (driving sprockets) do not skip. Driven sprockets
> do.
> Bill Sornson writes:>>>> Ah, an old classic of yours. Try riding mountain bikes and say
>>>> that chainwheels don't skip. I have a full XTR crankset that I
>>>> can't use because of ring wear. Chains skip like crazy on it
>>>> (small and middle rings for sure; probably not the big ring)...
jobst.brandt@stanfordalumni.org wrote:
>>> I'd like to see those CW's. They probably have no teeth and then
>>> you expect a wavy disk to work as a CW. I didn't say CW with only
>>> nubbins of teeth won't skip. Actually they don't, the slip, there
>>> being no digital arrest after each loss of drive.
> Bill Sornson writes:
>> The crankset looks perfectly normal, and in fact worked fine with
>> the old, badly worn chain. (As did the cassette.)
>> As I recall, the chain finally broke, and when I replaced it I got
>> horrible skipping. I assumed it was the cogs, so I replaced the
>> cassette. Still skipped -- mostly middle ring but little did, too.
>> This conforms to the experience I (and countless others) have had
>> with RaceFace, TruVativ, and other name-brand mtb chain rings: it's
>> why they sell replacement rings! (Affordable, too, BTW, unlike my
>> dusty XTR, for which a middle ring runs roughly 70 bucks.)
>> I remember you making this silly claim a few years ago, and I spoke
>> up then, too. Ask any mountain biker if they've worn out chain
>> rings and they will answer YES! It's not only common, it's
>> inevitable (assuming heavy use in dirty conditions).
>> Now I admit that I haven't seen this occur with my ROAD chain rings,
>> but then again I live in San Diego so seldom encounter rain or other
>> "grinding paste" conditions.
>> To sum up, chain rings can and do wear to the point of chain skip.
> Period.
jobst.brandt@stanfordalumni.org wrote:
> Well I posted a picture of a 47t chainwheel that had full height teeth
> that were paper thin and served well with new chains as did all of
> those of my riding pals who rode thier CW to death. I'll have to
> assume that this is not the way smaller CW behave, possibly because
> there being too few teeth engaged. I'm curious about the size of
> these CW's.
The #1 MTB replacement size is 36t and in high volume. They just wear
out. And quickly when used as intended - in gritty dirt. Also any
popular middle MTB ring- 34t 32t etc.
As Jobst notes, the worn tooth shape is radically different from a worn
rear tooth profile. As Bill Sornson notes, the net effect is the same.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
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Date: 29 Jun 2007 20:55:23
From: jim beam
Subject: Re: Safe to lengthen a chain?
|
jobst.brandt@stanfordalumni.org wrote:
> Bill Sornson writes:
>
>>>>> Chainwheels (driving sprockets) do not skip. Driven sprockets
> do.
>
>>>> Ah, an old classic of yours. Try riding mountain bikes and say
>>>> that chainwheels don't skip. I have a full XTR crankset that I
>>>> can't use because of ring wear. Chains skip like crazy on it
>>>> (small and middle rings for sure; probably not the big ring)...
>
>>> I'd like to see those CW's. They probably have no teeth and then
>>> you expect a wavy disk to work as a CW. I didn't say CW with only
>>> nubbins of teeth won't skip. Actually they don't, the slip, there
>>> being no digital arrest after each loss of drive.
>
>> The crankset looks perfectly normal, and in fact worked fine with
>> the old, badly worn chain. (As did the cassette.)
>
>> As I recall, the chain finally broke, and when I replaced it I got
>> horrible skipping. I assumed it was the cogs, so I replaced the
>> cassette. Still skipped -- mostly middle ring but little did, too.
>
>> This conforms to the experience I (and countless others) have had
>> with RaceFace, TruVativ, and other name-brand mtb chain rings: it's
>> why they sell replacement rings! (Affordable, too, BTW, unlike my
>> dusty XTR, for which a middle ring runs roughly 70 bucks.)
>
>> I remember you making this silly claim a few years ago, and I spoke
>> up then, too. Ask any mountain biker if they've worn out chain
>> rings and they will answer YES! It's not only common, it's
>> inevitable (assuming heavy use in dirty conditions).
>
>> Now I admit that I haven't seen this occur with my ROAD chain rings,
>> but then again I live in San Diego so seldom encounter rain or other
>> "grinding paste" conditions.
>
>> To sum up, chain rings can and do wear to the point of chain skip.
> Period.
>
> Well I posted a picture of a 47t chainwheel that had full height teeth
> that were paper thin and served well with new chains as did all of
> those of my riding pals who rode thier CW to death. I'll have to
> assume that this is not the way smaller CW behave, possibly because
> there being too few teeth engaged. I'm curious about the size of
> these CW's.
that data is strictly confidential - all websites that could inform are
password protected.
|
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Date: 29 Jun 2007 21:20:07
From: Bill Sornson
Subject: Re: Safe to lengthen a chain?
|
jim beam wrote:
> jobst.brandt@stanfordalumni.org wrote:
>> Bill Sornson writes:
>>
>>>>>> Chainwheels (driving sprockets) do not skip. Driven sprockets
>>>>>> do.
>>
>>>>> Ah, an old classic of yours. Try riding mountain bikes and say
>>>>> that chainwheels don't skip. I have a full XTR crankset that I
>>>>> can't use because of ring wear. Chains skip like crazy on it
>>>>> (small and middle rings for sure; probably not the big ring)...
>>
>>>> I'd like to see those CW's. They probably have no teeth and then
>>>> you expect a wavy disk to work as a CW. I didn't say CW with only
>>>> nubbins of teeth won't skip. Actually they don't, the slip, there
>>>> being no digital arrest after each loss of drive.
>>
>>> The crankset looks perfectly normal, and in fact worked fine with
>>> the old, badly worn chain. (As did the cassette.)
>>
>>> As I recall, the chain finally broke, and when I replaced it I got
>>> horrible skipping. I assumed it was the cogs, so I replaced the
>>> cassette. Still skipped -- mostly middle ring but little did, too.
>>
>>> This conforms to the experience I (and countless others) have had
>>> with RaceFace, TruVativ, and other name-brand mtb chain rings: it's
>>> why they sell replacement rings! (Affordable, too, BTW, unlike my
>>> dusty XTR, for which a middle ring runs roughly 70 bucks.)
>>
>>> I remember you making this silly claim a few years ago, and I spoke
>>> up then, too. Ask any mountain biker if they've worn out chain
>>> rings and they will answer YES! It's not only common, it's
>>> inevitable (assuming heavy use in dirty conditions).
>>
>>> Now I admit that I haven't seen this occur with my ROAD chain rings,
>>> but then again I live in San Diego so seldom encounter rain or other
>>> "grinding paste" conditions.
>>
>>> To sum up, chain rings can and do wear to the point of chain skip.
>>> Period.
>>
>> Well I posted a picture of a 47t chainwheel that had full height
>> teeth that were paper thin and served well with new chains as did
>> all of those of my riding pals who rode thier CW to death. I'll
>> have to assume that this is not the way smaller CW behave, possibly
>> because there being too few teeth engaged. I'm curious about the
>> size of these CW's.
>
> that data is strictly confidential - all websites that could inform
> are password protected.
LOL Yes, the specs of XTR cranksets are quite secret!
26-36-46. (Possibly 24-36-48.)
I guess JB will have to alter his categorical statement to "Big road
chainwheels (47T or larger) that I've personally seen do not skip." (Of
course, he could have listened to me years ago and conceded this point then,
but dearly held beliefs clearly do not give way readily.)
Whatever.
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Date: 29 Jun 2007 20:43:53
From: jim beam
Subject: Re: Safe to lengthen a chain?
|
Bill Sornson wrote:
> jobst.brandt@stanfordalumni.org wrote:
>> Bill Sornson writes:
>>> JB claimed: {missing attribution}
>
>>>> Chainwheels (driving sprockets) do not skip. Driven sprockets do.
>
>>> Ah, an old classic of yours. Try riding mountain bikes and say that
>>> chainwheels don't skip. I have a full XTR crankset that I can't use
>>> because of ring wear. Chains skip like crazy on it (small and
>>> middle rings for sure; probably not the big ring)...
>
>> I'd like to see those CW's. They probably have no teeth and then you
>> expect a wavy disk to work as a CW. I didn't say CW with only nubbins
>> of teeth won't skip. Actually they don't, the slip, there being no
>> digital arrest after each loss of drive.
>
> The crankset looks perfectly normal, and in fact worked fine with the old,
> badly worn chain. (As did the cassette.)
>
> As I recall, the chain finally broke, and when I replaced it I got horrible
> skipping. I assumed it was the cogs, so I replaced the cassette. Still
> skipped -- mostly middle ring but little did, too.
>
> This conforms to the experience I (and countless others) have had with
> RaceFace, TruVativ, and other name-brand mtb chain rings: it's why they
> sell replacement rings! (Affordable, too, BTW, unlike my dusty XTR, for
> which a middle ring runs roughly 70 bucks.)
>
> I remember you making this silly claim a few years ago, and I spoke up then,
> too. Ask any mountain biker if they've worn out chain rings and they will
> answer YES! It's not only common, it's inevitable (assuming heavy use in
> dirty conditions).
>
> Now I admit that I haven't seen this occur with my ROAD chain rings, but
> then again I live in San Diego so seldom encounter rain or other "grinding
> paste" conditions.
>
> To sum up, chain rings can and do wear to the point of chain skip. Period.
>
agreed - i have experience with this on mtb bikes. new chain rings make
the problem disappear immediately.
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Date: 29 Jun 2007 23:31:41
From: Sandy
Subject: Re: Safe to lengthen a chain?
|
Dans le message de news:46856c86$0$14069$742ec2ed@news.sonic.net,
jobst.brandt@stanfordalumni.org <jobst.brandt@stanfordalumni.org > a
réfléchi, et puis a déclaré :
>
> Well! Why is the event that caused the link to separate so illusive [sic]
> ?
Interesting choice of non-word, or rather, an interesting Spoonerism. I
know you are playing with us now, but your sense of humor is occasionally
elusive.
|
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Date: 29 Jun 2007 12:40:26
From: Tom Nakashima
Subject: Re: Safe to lengthen a chain?
|
<carlfogel@comcast.net > wrote in message
news:mdja83tpqkuf1fv1d0nff3k8qp62ulblqb@4ax.com...
> On Fri, 29 Jun 2007 06:42:13 -0700, "Tom Nakashima"
> <tom@slac.stanford.edu> wrote:
>
>>
>><carlfogel@comcast.net> wrote in message
>>news:77a883hb8e7sslso9435fs0j70a44feiom@4ax.com...
>>> On Thu, 28 Jun 2007 16:28:52 -0500, Tim McNamara
>>> <timmcn@bitstream.net> wrote:
>>>
>>> [snip]
>>>
>>>>If I understand Jobst's report correctly, he wasn't shifting gears. He
>>>>was climbing (which in his case is often a 47 x 13 kind of thing, from
>>>>what he's written in the past) and so pushing hard on the pedal. I
>>>>gather that the chain rode up the teeth of a worn 13T cog and then
>>>>skipped forward, snapping down into the next valley with an abrupt jolt.
>>>>There's lots of energy in those situations and the chain can get whipped
>>>>around pretty hard.
>>>
>>> [snip]
>>>
>>> Dear Tim,
>>>
>>> There is a lot of energy (or force), but there's also a lot of mass
>>> that may not be obvious.
>>>
>>> It's not just the four links of chain between the idler pulley and the
>>> 13-tooth gear that must speed up and slow down.
>>>
>>> It's the whole 100+ link chain wrapped around the two sprockets and
>>> the two idler pulleys, plus the entire crank, plus both the rider's
>>> legs that have to accelerate in half an inch of travel to a speed
>>> great enough that the linear momentum of those four links is enough to
>>> bang the quick-connect open.
>>>
>>> When I was thinking of whacking a loose chain with a hammer and Jobst
>>> was suggesting his more elegant idea of using a rubber band to fire a
>>> few links of chain against a pipe, we may both have been forgetting
>>> that our schemes involved an awful lot of speed that may not be
>>> possible in the real situation.
>>>
>>> Just to illustrate how the mass and acceleration and speed get tricky,
>>> here's a _bad_ example that I chased down.
>>>
>>> Imagine a bicycle propped up and standing still, with a rider standing
>>> on one foot on the leading pedal of a horizontal 175 mm crank with a
>>> 53-tooth sprocket.
>>>
>>> Obviously, his whole weight is pushing down on the pedal and putting a
>>> huge strain on the chain.
>>>
>>> Imagine the tremendous speed with which the chain will slam into the
>>> next tooth if it skips!
>>>
>>> It may be less than 1.43 mph. (Calculations to follow.)
>>>
>>> We tend to confuse the impressive force (the rider's whole weight!)
>>> with the acceleration.
>>>
>>> For a 175 mm crank, the pedal circle is 350 mm * 3.141 = 1100 mm.
>>>
>>> When the half-inch chain skips one link, the pedal on which the rider
>>> is standing acts like a hangman's trap and rotates 1/53 of the pedal
>>> circle.
>>>
>>> To simplify things, let's pretend that this small drop is straight
>>> down, instead of slightly curved: 1100 mm / 53 = 20.775 mm.
>>>
>>> Okay, I lied. I'm not going to calculate the speed of an object in
>>> free fall for 20.775 mm. Luckily there's a very precise free fall
>>> calculator that lets you stick a single value in, click, and get an
>>> answer:
>>>
>>> http://hyperphysics.phy-astr.gsu.edu/hbase/traj.html
>>>
>>> For 0.020775 meters, the calculator predicts a free-fall speed of
>>> 2.0935512 feet per second.
>>>
>>> Despite having Chalo standing on the pedal when it skips, the pedal
>>> _may_ reach a speed of only 1.43 miles per hour. (Caveats follow.)
>>>
>>> Meanwhile, back at the 13-tooth, the chain has moved only half an
>>> inch, about 12.7 mm, less than the pedal--so it's going even slower.
>>>
>>> The _leading_ link beyond the quick-connect might break the gear tooth
>>> off because of its tremendous force.
>>>
>>> But the short section of a couple of chain links _trailing_ behind the
>>> quick connect will "slam" into the back of the decelerating
>>> quick-connect link at less than 1.5 mph. You can develop far more
>>> impact than this by flicking your fingernail against a quick-connect.
>>>
>>> So why is this a bad example?
>>>
>>> I see two potential problems.
>>>
>>> First, what if there's a lot more force stored up spring-style in the
>>> frame, crank, and taut chain? More force with the same mass would
>>> produce a greater acceleration. If Chalo is teetering motionless on
>>> the leading pedal of a bike standing still, the metal parts may be
>>> stretched a lot more than the naive example expected.
>>>
>>> Release a stretched rubber band, and you can get far more acceleration
>>> than mere free-fall.
>>>
>>> But I don't know how to calculate this effect theoretically or measure
>>> it practically.
>>>
>>> Second, the rider may can probably generate a _faster_ skip when he's
>>> sitting instead of standing on the pedal.
>>>
>>> The absolute speed is what matters, not the raw force. It's the ratio
>>> of total mass to available force that determines acceleration and
>>> impact speed in our half-inch sprint.
>>>
>>> By sitting and using muscle instead of gravity, the rider can increase
>>> the force and reduce the mass that must be accelerated. (He still has
>>> to accelerate both his legs to some degree--remember, his rear leg has
>>> to accelerate up just as much as his front leg accelerates down.)
>>>
>>> A feeble rubber band can accelerate a four-inch chain section enough
>>> in about three inches to fling it fifty feet--I tried it in my
>>> driveway.
>>>
>>> But it's the ratio of the rubber band's feeble force to the tiny mass
>>> of the handful of chain links that makes this impressive acceleration
>>> possible.
>>>
>>> Use the same rubber band to try to spin a pedal and crank against the
>>> chain and freewheel, and you get less than a quarter-turn of movement.
>>> No human eye can tell how fast the pedal is moving in that first half
>>> inch or so, but things are obviously flying only about a foot, roughly
>>> two orders of magnitude less than fifty feet.
>>>
>>> So I still don't know how to predict in theory or measure in practice
>>> the speed with which a skipping chain decelerates as it slams into the
>>> next position on the 13-tooth. And it's the speed that determines
>>> whether the short section of chain between the idler pulley and the
>>> 13-tooth has enough force to bang the two halves of a quick-connect
>>> link together and release them.
>>>
>>> Cheers,
>>>
>>> Carl Fogel
>>
>>Carl, maybe it's not the force that separated the quick-connect link?
>>Climbing in a 47/13 (not sure how steep the climb was) on steep climbs
>>a cyclist sometimes squares his pedals, meaning not a smooth rotation
>>of the pedals, but hesitates. This hesitation causes backlash (slack) in
>>the chain. If the quick-connect wasn't installed properly (didn't
>>lock in) it's possible for the side plate to disengage. I'm not saying
>>Jobst didn't install the quick-connect properly. I can recall I had once
>>not
>>heard a clicking sound of the sideplates engaging into the grooves when I
>>installed a PowerLink. When I checked it on a bike stand, it easily came
>>apart. There's a groove that the side plate has to engage into, sometimes
>>the plate has a hard time finding it's way into that groove.
>>http://www.hostelshoppe.com/images/products/la_sram_powerlink.jpg
>>-tom
>
> Dear Tom,
>
> You've come up with another possibility for a quick-connect
> separating.
>
> If a rider suffers a chain skip at just the wrong moment near the
> bottom of the pedal cycle, he might get a back-lash, wave, flip, or
> whatever it's called. If this causes the double arm of the derailleur
> to go boing! and the quick-connect in just the right spot, the motion
> might compress the two half-links enough for them to separate.
>
> That suggests an even more dramatic possibility. The Z-bend in the
> derailleur doesn't always handle bouncing very well. A chain skip
> coupled with a bump in the road might bounce a chain enough to get
> cross-wise with the idler pulleys or gear cluster and jam. If the
> quick-connect is in just the right spot, it might come apart when a
> chain jams, whereupon the chain falls off and leaves no sign of the
> jam.
>
> Whatever happened seems to be an extremely rare event. I'm interested
> in Jobst's explanation, partly because it leads to so many curious
> details and partly because it leads to so many dogmatic claims that
> lead to more curious details. If Jobst's theory is correct, it should
> be able to withstand some questions. If not, it still raises
> interesting questions. And whether he's right or wrong, he deserves
> credit for posting a plausible explanation--look how much fun you and
> I are having wondering about how a quick-connect might come apart.
>
> Cheers,
>
> Carl Fogel
We can probably rule out the possibility of the back-lash theory if the
quick-connect link was installed correctly. I called Sram this morning
and spoke with their RD department. They had really put this quick-
connect link to the test. I didn't know the design has been out for over 10
years. The tech I spoke with said there is NO-WAY the quick-connect
will come apart when installed correctly on a chain when riding. The RD
department tried all the possibilities, including making a daisy chain
out of their quick-connect links and running them through all possible
drivetrain motions a bicycle would go through.
If Jobst said his quick-connect link came apart, then I'll just leave it
at that. I will still continue to use the Sram PowerLink. And someday
if I have a mishap and my PowerLink fails, I will too post about the chain
of events, but I hope that day will never come.
-tom
|
| | | | | | | | |
Date: 29 Jun 2007 15:38:28
From: Bill Sornson
Subject: Re: Safe to lengthen a chain?
|
Tom Nakashima wrote:
{Hugh Jass Memorial Snip}
> We can probably rule out the possibility of the back-lash theory if
> the quick-connect link was installed correctly. I called Sram this
> morning and spoke with their RD department. They had really put this
> quick-
> connect link to the test. I didn't know the design has been out for
> over 10 years. The tech I spoke with said there is NO-WAY the
> quick-connect will come apart when installed correctly on a chain when
> riding. The
> RD department tried all the possibilities, including making a daisy
> chain out of their quick-connect links and running them through all
> possible
> drivetrain motions a bicycle would go through.
>
> If Jobst said his quick-connect link came apart, then I'll just leave
> it at that. I will still continue to use the Sram PowerLink. And someday
> if I have a mishap and my PowerLink fails, I will too post about the
> chain of events, but I hope that day will never come.
"Chain of events" -- nice. :-P
Bill "5 or 6 broken chains in 12 years; never had a PowerLink fail or come
apart" S.
|
| | | | | | | | |
Date: 29 Jun 2007 14:43:25
From:
Subject: Re: Safe to lengthen a chain?
|
On Fri, 29 Jun 2007 12:40:26 -0700, "Tom Nakashima"
<tom@slac.stanford.edu > wrote:
>We can probably rule out the possibility of the back-lash theory if the
>quick-connect link was installed correctly. I called Sram this morning
>and spoke with their RD department. They had really put this quick-
>connect link to the test. I didn't know the design has been out for over 10
>years. The tech I spoke with said there is NO-WAY the quick-connect
>will come apart when installed correctly on a chain when riding. The RD
>department tried all the possibilities, including making a daisy chain
>out of their quick-connect links and running them through all possible
>drivetrain motions a bicycle would go through.
>
>If Jobst said his quick-connect link came apart, then I'll just leave it
>at that. I will still continue to use the Sram PowerLink. And someday
>if I have a mishap and my PowerLink fails, I will too post about the chain
>of events, but I hope that day will never come.
>-tom
Dear Tom,
Thanks--I love odd details like this.
I like the idea of using an all-quick-connect chain.
But a chain made up entirely of quick-connect links may actually be
less to fail in Jobst's scenario.
Right after a chain skip, Jobst reasons, the short section of chain
between the idler pulley and the derailleur is still going at skip
speed, so it crashes into the back of the quick-connect link, which
has stalled behind the link that has banged into first gear tooth.
If the quick-connect is banged hard enough, the two half-links can
compress and the quick-connect can fall apart.
But if every link in that short section of chain is a quick-connect,
then each link may compress just a little, unlike the normal single
link that compresses a lot.
I don't know whether the company tested skipping chains, but I'm
always skeptical of people who announce that there's NO-WAY that
something can fail.
But I do know that chains with quick-connects fall apart so rarely
that most of us have never seen it happen, so I think that the company
is giving a good-faith answer. They also probably did more testing
than we can imagine--given the price of quick-connects, I wouldn't
think of fmaking a whole chain out of them.
Cheers,
Carl Fogel
|
| | | | | | | | | |
Date: 29 Jun 2007 13:57:59
From: Tom Nakashima
Subject: Re: Safe to lengthen a chain?
|
<carlfogel@comcast.net > wrote in message
news:glqa83hu0l4mk6h0bavbluf5ks0g6ftrii@4ax.com...
> On Fri, 29 Jun 2007 12:40:26 -0700, "Tom Nakashima"
> <tom@slac.stanford.edu> wrote:
>
>>We can probably rule out the possibility of the back-lash theory if the
>>quick-connect link was installed correctly. I called Sram this morning
>>and spoke with their RD department. They had really put this quick-
>>connect link to the test. I didn't know the design has been out for over
>>10
>>years. The tech I spoke with said there is NO-WAY the quick-connect
>>will come apart when installed correctly on a chain when riding. The RD
>>department tried all the possibilities, including making a daisy chain
>>out of their quick-connect links and running them through all possible
>>drivetrain motions a bicycle would go through.
>>
>>If Jobst said his quick-connect link came apart, then I'll just leave it
>>at that. I will still continue to use the Sram PowerLink. And someday
>>if I have a mishap and my PowerLink fails, I will too post about the chain
>>of events, but I hope that day will never come.
>>-tom
>
> Dear Tom,
>
> Thanks--I love odd details like this.
>
> I like the idea of using an all-quick-connect chain.
>
> But a chain made up entirely of quick-connect links may actually be
> less to fail in Jobst's scenario.
>
> Right after a chain skip, Jobst reasons, the short section of chain
> between the idler pulley and the derailleur is still going at skip
> speed, so it crashes into the back of the quick-connect link, which
> has stalled behind the link that has banged into first gear tooth.
>
> If the quick-connect is banged hard enough, the two half-links can
> compress and the quick-connect can fall apart.
>
> But if every link in that short section of chain is a quick-connect,
> then each link may compress just a little, unlike the normal single
> link that compresses a lot.
Well not every link, as we all know there has to be a section of chain
in order to use the PowerLink connector, which I wouldn't mind decorating
our Xmas tree this year instead of using popcorn strings.
>
> I don't know whether the company tested skipping chains, but I'm
> always skeptical of people who announce that there's NO-WAY that
> something can fail.
I do agree with you on the NO-WAY clause. A defect in the part
or "weak-link" (no pun intended) will negate that.
>
> But I do know that chains with quick-connects fall apart so rarely
> that most of us have never seen it happen, so I think that the company
> is giving a good-faith answer. They also probably did more testing
> than we can imagine--given the price of quick-connects, I wouldn't
> think of fmaking a whole chain out of them.
>
> Cheers,
>
> Carl Fogel
Then again I somewhat feel the "SalesPitch" to use my product.
I can only say, the PowerLink hasn't failed me in the last 3-years.
I don't carry a chain tool either, but I guess my metal tire-irons make
up the weight.
I feel Jobst is thinking we're making a mockery out of this.
I hope there is no bad feelings. Sometimes we disagree here in RBT.
no harm/ no foul.
-tom
|
| | | | | | | | | | |
Date: 29 Jun 2007 23:04:10
From: still me
Subject: Re: Safe to lengthen a chain?
|
On Fri, 29 Jun 2007 13:57:59 -0700, "Tom Nakashima"
<tom@slac.stanford.edu > wrote:
>Then again I somewhat feel the "SalesPitch" to use my product.
>I can only say, the PowerLink hasn't failed me in the last 3-years.
>I don't carry a chain tool either, but I guess my metal tire-irons make
>up the weight.
That's why you need to be riding tubulars!
|
| | | | | | | | | | |
Date: 29 Jun 2007 15:44:08
From: Bill Sornson
Subject: Re: Safe to lengthen a chain?
|
Tom Nakashima wrote:
> Then again I somewhat feel the "SalesPitch" to use my product.
> I can only say, the PowerLink hasn't failed me in the last 3-years.
> I don't carry a chain tool either, but I guess my metal tire-irons
> make up the weight.
What will you do if you break a chain away from the PowerLink? I carry a
little multi-tool that includes a chain breaker, spoke wrench, basic keys
and driver heads, etc. Also a spare PL.
> I feel Jobst is thinking we're making a mockery out of this.
> I hope there is no bad feelings. Sometimes we disagree here in RBT.
> no harm/ no foul.
You dreamer you! LOL
Bill "whaddya, new?" S.
|
| | | | | | | | |
Date: 29 Jun 2007 20:18:31
From:
Subject: Re: Safe to lengthen a chain?
|
Tom Nakashima writes:
> We can probably rule out the possibility of the back-lash theory if
> the quick-connect link was installed correctly. I called SRAM this
> morning and spoke with their RD department. They had really put
> this quick- connect link to the test. I didn't know the design has
> been out for over 10 years. The tech I spoke with said there is
> NO-WAY the quick-connect will come apart when installed correctly on
> a chain when riding. The RD department tried all the possibilities,
> including making a daisy chain out of their quick-connect links and
> running them through all possible drivetrain motions a bicycle would
> go through.
> If Jobst said his quick-connect link came apart, then I'll just
> leave it at that. I will still continue to use the SRAM
> PowerLink. And someday if I have a mishap and my PowerLink fails, I
> will too post about the chain of events, but I hope that day will
> never come.
I don't understand what moves you to present this event as a current
and present danger when using a SuperLink. I never said that it was
one and reported it mainly because I found it an oddity and rare
occurrence. Yet you and others insist that I warn of the hazards of
SuperLinks. You'll have to quote that text to convince me. Meanwhile
stop wringing your hands about possibilities.
My point was that for my use, I see no advantage in separable links
because my chain is one that can be separated and re-attache using a
chain tool, one that I would need (and have) in the event of a
derailleur failure (twig in the chain). My riding companions can
relate similar experience from Gazos Creek and Last chance roads, for
instance.
Jobst Brandt
|
| | | | | | | | | |
Date: 29 Jun 2007 13:35:52
From: Tom Nakashima
Subject: Re: Safe to lengthen a chain?
|
<jobst.brandt@stanfordalumni.org > wrote in message
news:46856917$0$14069$742ec2ed@news.sonic.net...
> Tom Nakashima writes:
>
>> We can probably rule out the possibility of the back-lash theory if
>> the quick-connect link was installed correctly. I called SRAM this
>> morning and spoke with their RD department. They had really put
>> this quick- connect link to the test. I didn't know the design has
>> been out for over 10 years. The tech I spoke with said there is
>> NO-WAY the quick-connect will come apart when installed correctly on
>> a chain when riding. The RD department tried all the possibilities,
>> including making a daisy chain out of their quick-connect links and
>> running them through all possible drivetrain motions a bicycle would
>> go through.
>
>> If Jobst said his quick-connect link came apart, then I'll just
>> leave it at that. I will still continue to use the SRAM
>> PowerLink. And someday if I have a mishap and my PowerLink fails, I
>> will too post about the chain of events, but I hope that day will
>> never come.
>
> I don't understand what moves you to present this event as a current
> and present danger when using a SuperLink.
I never presented this event as a present danger when using a PowerLink.
I said I had never had a failure while using them in the past 3 years.
> I never said that it was
> one and reported it mainly because I found it an oddity and rare
> occurrence.
Yes, I do agree it is an oddity and rare occurrence.
As I said in my post, as you said in your chain of events that your
quick-connect link came apart..."then I'll leave it at that".
>Yet you and others insist that I warn of the hazards of
> SuperLinks.
I don't think anyone here is suggesting that. There are many here who
value your words, and we are grateful for your contributions to the group.
> You'll have to quote that text to convince me. Meanwhile
> stop wringing your hands about possibilities.
I did say I'll leave it at that.
> My point was that for my use, I see no advantage in separable links
> because my chain is one that can be separated and re-attache using a
> chain tool, one that I would need (and have) in the event of a
> derailleur failure (twig in the chain). My riding companions can
> relate similar experience from Gazos Creek and Last chance roads, for
> instance.
>
> Jobst Brandt
When you post Jobst, I should take it that everything you do is for your
use only? Why bother posting?
Yes I do understand that you use a chain-tool, and I, after having
success with the Sram PowerLink will continue to do so.
-tom
|
| | | | | |
Date: 29 Jun 2007 00:33:20
From: Tim McNamara
Subject: Re: Safe to lengthen a chain?
|
In article <77a883hb8e7sslso9435fs0j70a44feiom@4ax.com >,
carlfogel@comcast.net wrote:
> On Thu, 28 Jun 2007 16:28:52 -0500, Tim McNamara
> <timmcn@bitstream.net> wrote:
>
> [snip]
>
> >If I understand Jobst's report correctly, he wasn't shifting gears.
> >He was climbing (which in his case is often a 47 x 13 kind of thing,
> >from what he's written in the past) and so pushing hard on the
> >pedal. I gather that the chain rode up the teeth of a worn 13T cog
> >and then skipped forward, snapping down into the next valley with an
> >abrupt jolt. There's lots of energy in those situations and the
> >chain can get whipped around pretty hard.
>
> [snip]
>
> Dear Tim,
>
> There is a lot of energy (or force), but there's also a lot of mass
> that may not be obvious.
>
> It's not just the four links of chain between the idler pulley and
> the 13-tooth gear that must speed up and slow down.
>
> It's the whole 100+ link chain wrapped around the two sprockets and
> the two idler pulleys, plus the entire crank, plus both the rider's
> legs that have to accelerate in half an inch of travel to a speed
> great enough that the linear momentum of those four links is enough
> to bang the quick-connect open.
Ummm, I don't think so- not that this is any guarantee of correctness.
The chain at the cog snaps forward 1/2". But the chainwheel only
advances a fraction of that- consider a 48T chainring and a 12 tooth
sprocket: the chainring advances 1/4 as far so 1/8". That's why it's
not all that noticeable through your feet and is mainly an acoustic
event for the rider (but with skipping on the larger sprockets and/or
with a smaller chainring, the chainring would advance farther and feels
more noticeable). Once the chain has skipped over the top of the
sprocket tooth and re-engaged the sprocket, the PowerLink in the
position postulated would be isolated from the forces on the top run of
the chain and those could be ignored along with the rider's legs. I
think.
If correct, this simplifies the construction quite a bit. We can ignore
most of the chain as well as the chainrings and the legs of the rider
because those things are isolated from the PowerLink. The area of
interest is the chain from the last engaged tooth on the chainring (the
exit tooth) to the first tooth on the sprocket (the entry tooth). This
section of the chain is under low tension and the chain is remarkably
free to flop around as seen in many photos of cyclists on a bumpy
surface.
The linear momentum in this case would not the linear momentum from
pedaling- which is rather slow, actually- but a wave form snapped
through the chain like a bullwhip going back to the last flexible part
of the system- the PowerLink anchored against the tooth of the sprocket.
The wave could even be reflected back and forth from the endpoints (we
all did stuff like that in high school physics, right?) and might even
push and then pull on the PowerLink. In any events, the energy can't get
past the entry tooth and so the PowerLink bears the brunt. It's
compressed, there's just enough lateral shear from the jockey wheel and
the sprocket being slightly misaligned, and pingo!
Or maybe not. I could be all wet. The question I have for my own
scenario is why doesn't the derailleur protect the PowerLink from the
bullwhip like wave coming through the chain? Could the derailleur get
flung back into the PowerLink and snap it open?
|
| | | | | | |
Date: 29 Jun 2007 13:22:38
From:
Subject: Re: Safe to lengthen a chain?
|
On Fri, 29 Jun 2007 00:33:20 -0500, Tim McNamara
<timmcn@bitstream.net > wrote:
>In article <77a883hb8e7sslso9435fs0j70a44feiom@4ax.com>,
> carlfogel@comcast.net wrote:
>
>> On Thu, 28 Jun 2007 16:28:52 -0500, Tim McNamara
>> <timmcn@bitstream.net> wrote:
>>
>> [snip]
>>
>> >If I understand Jobst's report correctly, he wasn't shifting gears.
>> >He was climbing (which in his case is often a 47 x 13 kind of thing,
>> >from what he's written in the past) and so pushing hard on the
>> >pedal. I gather that the chain rode up the teeth of a worn 13T cog
>> >and then skipped forward, snapping down into the next valley with an
>> >abrupt jolt. There's lots of energy in those situations and the
>> >chain can get whipped around pretty hard.
>>
>> [snip]
>>
>> Dear Tim,
>>
>> There is a lot of energy (or force), but there's also a lot of mass
>> that may not be obvious.
>>
>> It's not just the four links of chain between the idler pulley and
>> the 13-tooth gear that must speed up and slow down.
>>
>> It's the whole 100+ link chain wrapped around the two sprockets and
>> the two idler pulleys, plus the entire crank, plus both the rider's
>> legs that have to accelerate in half an inch of travel to a speed
>> great enough that the linear momentum of those four links is enough
>> to bang the quick-connect open.
>
>Ummm, I don't think so- not that this is any guarantee of correctness.
>
>The chain at the cog snaps forward 1/2". But the chainwheel only
>advances a fraction of that- consider a 48T chainring and a 12 tooth
>sprocket: the chainring advances 1/4 as far so 1/8". That's why it's
>not all that noticeable through your feet and is mainly an acoustic
>event for the rider (but with skipping on the larger sprockets and/or
>with a smaller chainring, the chainring would advance farther and feels
>more noticeable). Once the chain has skipped over the top of the
>sprocket tooth and re-engaged the sprocket, the PowerLink in the
>position postulated would be isolated from the forces on the top run of
>the chain and those could be ignored along with the rider's legs. I
>think.
>
>If correct, this simplifies the construction quite a bit. We can ignore
>most of the chain as well as the chainrings and the legs of the rider
>because those things are isolated from the PowerLink. The area of
>interest is the chain from the last engaged tooth on the chainring (the
>exit tooth) to the first tooth on the sprocket (the entry tooth). This
>section of the chain is under low tension and the chain is remarkably
>free to flop around as seen in many photos of cyclists on a bumpy
>surface.
>
>The linear momentum in this case would not the linear momentum from
>pedaling- which is rather slow, actually- but a wave form snapped
>through the chain like a bullwhip going back to the last flexible part
>of the system- the PowerLink anchored against the tooth of the sprocket.
>The wave could even be reflected back and forth from the endpoints (we
>all did stuff like that in high school physics, right?) and might even
>push and then pull on the PowerLink. In any events, the energy can't get
>past the entry tooth and so the PowerLink bears the brunt. It's
>compressed, there's just enough lateral shear from the jockey wheel and
>the sprocket being slightly misaligned, and pingo!
>
>Or maybe not. I could be all wet. The question I have for my own
>scenario is why doesn't the derailleur protect the PowerLink from the
>bullwhip like wave coming through the chain? Could the derailleur get
>flung back into the PowerLink and snap it open?
Dear Tim,
I may be all wet, too, but I _think_ that a 48-tooth chainwheel
advances exactly as far as a 12-tooth rear sprocket, half an inch.
That is, the absolute distance is what matters, not the degrees of
rotation.
When the chain skips on the rear, it does so by each link engaging
higher and higher on the rear teeth until all the links touching the
rear teeth are near the tips of the teeth--and then they all slip over
the top at once and skip into the next position.
So the whole linear chain (which wraps around two sprockets and makes
a Z-bend through the derailleur pulleys) skips forward half an inch.
It doesn't matter whether the chain is motionless or doing its feeble
1.5 to 2.5 mph at 60 to 90 rpm--the skip speed is relative to whatever
the current speed is.
Here's a diagram just to remind us of the chain path:
http://i9.tinypic.com/4v38hhl.jpg
Once the chain jumps into the new position, the links hitting the
teeth stop dead relative to their skip speed. But the links just
behind them, the short section feeding onto the rear sprocket, are
loose in that they swing from the spring-loaded double-arm of the
derailleur.
So Jobst's idea is that the short length of chain on the rear
derailleur sped up, too, when the skip started, and is free to crash
into the "stopped" links that have re-engaged the 13-tooth. If the
quick-link is just short of the rear cluster, then the short lengh of
chain behind it will still be going faster, might bang into it, and
could compress and separate the two half links.
The question for his theory is how fast the does a chain actually go
relative to its original speed? Since the distance involved is only
half an inch, we need an impressive acceleration to bang things
together. He's certain that it's plenty fast enough. I'm still looking
for evidence.
Your idea about a reflected shock wave may well work, too, though I
have no idea what the details would be.
As for the spring-loaded derailleur going boing! and somehow jamming
the quick-connect half-links together, that seems like a possibility,
particularly if the chain skip occurs just when the bike hits a bump.
Jobst's explanation seems plausible to me, but only if we get a lot of
speed in half an inch of skip. Other explanations are also
plausible--a defective link, a good link not quite fitting completely
together, or a chain jam that hid itself by compressing the link and
then falling off.
Whatever happened, it seems to be so rare that it's going to be
interesting to explain.
It's so hard to duplicate the actual event that we can only advance
theories and perform what may be only faintly related experiments, but
we can still learn a lot even if we never agree about the explanation.
Cheers,
Carl Fogel
|
| | | | | | | |
Date: 30 Jun 2007 11:37:38
From: Tim McNamara
Subject: Re: Safe to lengthen a chain?
|
In article <r2la83dubtsjer9r5ov88k73b2ot07m5km@4ax.com >,
carlfogel@comcast.net wrote:
> On Fri, 29 Jun 2007 00:33:20 -0500, Tim McNamara
> <timmcn@bitstream.net> wrote:
>
> >In article <77a883hb8e7sslso9435fs0j70a44feiom@4ax.com>,
> > carlfogel@comcast.net wrote:
> >
> >> On Thu, 28 Jun 2007 16:28:52 -0500, Tim McNamara
> >> <timmcn@bitstream.net> wrote:
> >>
> >> [snip]
> >>
> >> >If I understand Jobst's report correctly, he wasn't shifting
> >> >gears. He was climbing (which in his case is often a 47 x 13
> >> >kind of thing, from what he's written in the past) and so pushing
> >> >hard on the pedal. I gather that the chain rode up the teeth of
> >> >a worn 13T cog and then skipped forward, snapping down into the
> >> >next valley with an abrupt jolt. There's lots of energy in those
> >> >situations and the chain can get whipped around pretty hard.
> >>
> >> [snip]
> >>
> >> Dear Tim,
> >>
> >> There is a lot of energy (or force), but there's also a lot of
> >> mass that may not be obvious.
> >>
> >> It's not just the four links of chain between the idler pulley and
> >> the 13-tooth gear that must speed up and slow down.
> >>
> >> It's the whole 100+ link chain wrapped around the two sprockets
> >> and the two idler pulleys, plus the entire crank, plus both the
> >> rider's legs that have to accelerate in half an inch of travel to
> >> a speed great enough that the linear momentum of those four links
> >> is enough to bang the quick-connect open.
> >
> >Ummm, I don't think so- not that this is any guarantee of
> >correctness.
> >
> >The chain at the cog snaps forward 1/2". But the chainwheel only
> >advances a fraction of that- consider a 48T chainring and a 12 tooth
> >sprocket: the chainring advances 1/4 as far so 1/8". That's why
> >it's not all that noticeable through your feet and is mainly an
> >acoustic event for the rider (but with skipping on the larger
> >sprockets and/or with a smaller chainring, the chainring would
> >advance farther and feels more noticeable). Once the chain has
> >skipped over the top of the sprocket tooth and re-engaged the
> >sprocket, the PowerLink in the position postulated would be isolated
> >from the forces on the top run of the chain and those could be
> >ignored along with the rider's legs. I think.
> >
> >If correct, this simplifies the construction quite a bit. We can
> >ignore most of the chain as well as the chainrings and the legs of
> >the rider because those things are isolated from the PowerLink. The
> >area of interest is the chain from the last engaged tooth on the
> >chainring (the exit tooth) to the first tooth on the sprocket (the
> >entry tooth). This section of the chain is under low tension and
> >the chain is remarkably free to flop around as seen in many photos
> >of cyclists on a bumpy surface.
> >
> >The linear momentum in this case would not the linear momentum from
> >pedaling- which is rather slow, actually- but a wave form snapped
> >through the chain like a bullwhip going back to the last flexible
> >part of the system- the PowerLink anchored against the tooth of the
> >sprocket. The wave could even be reflected back and forth from the
> >endpoints (we all did stuff like that in high school physics,
> >right?) and might even push and then pull on the PowerLink. In any
> >events, the energy can't get past the entry tooth and so the
> >PowerLink bears the brunt. It's compressed, there's just enough
> >lateral shear from the jockey wheel and the sprocket being slightly
> >misaligned, and pingo!
> >
> >Or maybe not. I could be all wet. The question I have for my own
> >scenario is why doesn't the derailleur protect the PowerLink from
> >the bullwhip like wave coming through the chain? Could the
> >derailleur get flung back into the PowerLink and snap it open?
>
> Dear Tim,
>
> I may be all wet, too, but I _think_ that a 48-tooth chainwheel
> advances exactly as far as a 12-tooth rear sprocket, half an inch.
>
> That is, the absolute distance is what matters, not the degrees of
> rotation.
Pondering that I think you may be correct. However, OTOH, I find that a
skipping chain on a large sprocket is more noticeable through the feet
than skipping on a small sprocket.
> When the chain skips on the rear, it does so by each link engaging
> higher and higher on the rear teeth until all the links touching the
> rear teeth are near the tips of the teeth--and then they all slip
> over the top at once and skip into the next position.
>
> So the whole linear chain (which wraps around two sprockets and makes
> a Z-bend through the derailleur pulleys) skips forward half an inch.
> It doesn't matter whether the chain is motionless or doing its feeble
> 1.5 to 2.5 mph at 60 to 90 rpm--the skip speed is relative to
> whatever the current speed is.
When the chain skips, what is the effective rpm during that moment of
free acceleration? The chain skip is most likely to occur with the
leading leg at roughly 2:00-4:00, facing the chainring, which is the
highest range of force from either the muscles or the weight of the
rider on the pedal. Could the effective rpm for that brief moment be,
say 200 rpm instead of 90? That would change the picture a bit.
> Here's a diagram just to remind us of the chain path:
>
> http://i9.tinypic.com/4v38hhl.jpg
>
> Once the chain jumps into the new position, the links hitting the
> teeth stop dead relative to their skip speed. But the links just
> behind them, the short section feeding onto the rear sprocket, are
> loose in that they swing from the spring-loaded double-arm of the
> derailleur.
>
> So Jobst's idea is that the short length of chain on the rear
> derailleur sped up, too, when the skip started, and is free to crash
> into the "stopped" links that have re-engaged the 13-tooth. If the
> quick-link is just short of the rear cluster, then the short lengh of
> chain behind it will still be going faster, might bang into it, and
> could compress and separate the two half links.
>
> The question for his theory is how fast the does a chain actually go
> relative to its original speed? Since the distance involved is only
> half an inch, we need an impressive acceleration to bang things
> together. He's certain that it's plenty fast enough. I'm still
> looking for evidence.
Again, you are thinking about chain velocity as the product of pedaling
speed 60-90 rpm. But what if, for that brief time interval, the
effective rpm was 200 rpm? Or what if the energy traveling through the
chain was not simply the linear velocity of the chain as pedaled but a
whip-crack of energy being snapped through the chain? Could there be an
addition of stored energy in the frame that is released into the chain?
> Your idea about a reflected shock wave may well work, too, though I
> have no idea what the details would be.
>
> As for the spring-loaded derailleur going boing! and somehow jamming
> the quick-connect half-links together, that seems like a possibility,
> particularly if the chain skip occurs just when the bike hits a bump.
>
> Jobst's explanation seems plausible to me, but only if we get a lot
> of speed in half an inch of skip. Other explanations are also
> plausible--a defective link, a good link not quite fitting completely
> together, or a chain jam that hid itself by compressing the link and
> then falling off.
>
> Whatever happened, it seems to be so rare that it's going to be
> interesting to explain.
>
> It's so hard to duplicate the actual event that we can only advance
> theories and perform what may be only faintly related experiments,
> but we can still learn a lot even if we never agree about the
> explanation.
>
> Cheers,
>
> Carl Fogel
|
| | | | | | | | |
Date: 30 Jun 2007 13:27:47
From:
Subject: Re: Safe to lengthen a chain?
|
On Sat, 30 Jun 2007 11:37:38 -0500, Tim McNamara
<timmcn@bitstream.net > wrote:
>In article <r2la83dubtsjer9r5ov88k73b2ot07m5km@4ax.com>,
> carlfogel@comcast.net wrote:
>
>> On Fri, 29 Jun 2007 00:33:20 -0500, Tim McNamara
>> <timmcn@bitstream.net> wrote:
>>
>> >In article <77a883hb8e7sslso9435fs0j70a44feiom@4ax.com>,
>> > carlfogel@comcast.net wrote:
>> >
>> >> On Thu, 28 Jun 2007 16:28:52 -0500, Tim McNamara
>> >> <timmcn@bitstream.net> wrote:
>> >>
>> >> [snip]
>> >>
>> >> >If I understand Jobst's report correctly, he wasn't shifting
>> >> >gears. He was climbing (which in his case is often a 47 x 13
>> >> >kind of thing, from what he's written in the past) and so pushing
>> >> >hard on the pedal. I gather that the chain rode up the teeth of
>> >> >a worn 13T cog and then skipped forward, snapping down into the
>> >> >next valley with an abrupt jolt. There's lots of energy in those
>> >> >situations and the chain can get whipped around pretty hard.
>> >>
>> >> [snip]
>> >>
>> >> Dear Tim,
>> >>
>> >> There is a lot of energy (or force), but there's also a lot of
>> >> mass that may not be obvious.
>> >>
>> >> It's not just the four links of chain between the idler pulley and
>> >> the 13-tooth gear that must speed up and slow down.
>> >>
>> >> It's the whole 100+ link chain wrapped around the two sprockets
>> >> and the two idler pulleys, plus the entire crank, plus both the
>> >> rider's legs that have to accelerate in half an inch of travel to
>> >> a speed great enough that the linear momentum of those four links
>> >> is enough to bang the quick-connect open.
>> >
>> >Ummm, I don't think so- not that this is any guarantee of
>> >correctness.
>> >
>> >The chain at the cog snaps forward 1/2". But the chainwheel only
>> >advances a fraction of that- consider a 48T chainring and a 12 tooth
>> >sprocket: the chainring advances 1/4 as far so 1/8". That's why
>> >it's not all that noticeable through your feet and is mainly an
>> >acoustic event for the rider (but with skipping on the larger
>> >sprockets and/or with a smaller chainring, the chainring would
>> >advance farther and feels more noticeable). Once the chain has
>> >skipped over the top of the sprocket tooth and re-engaged the
>> >sprocket, the PowerLink in the position postulated would be isolated
>> >from the forces on the top run of the chain and those could be
>> >ignored along with the rider's legs. I think.
>> >
>> >If correct, this simplifies the construction quite a bit. We can
>> >ignore most of the chain as well as the chainrings and the legs of
>> >the rider because those things are isolated from the PowerLink. The
>> >area of interest is the chain from the last engaged tooth on the
>> >chainring (the exit tooth) to the first tooth on the sprocket (the
>> >entry tooth). This section of the chain is under low tension and
>> >the chain is remarkably free to flop around as seen in many photos
>> >of cyclists on a bumpy surface.
>> >
>> >The linear momentum in this case would not the linear momentum from
>> >pedaling- which is rather slow, actually- but a wave form snapped
>> >through the chain like a bullwhip going back to the last flexible
>> >part of the system- the PowerLink anchored against the tooth of the
>> >sprocket. The wave could even be reflected back and forth from the
>> >endpoints (we all did stuff like that in high school physics,
>> >right?) and might even push and then pull on the PowerLink. In any
>> >events, the energy can't get past the entry tooth and so the
>> >PowerLink bears the brunt. It's compressed, there's just enough
>> >lateral shear from the jockey wheel and the sprocket being slightly
>> >misaligned, and pingo!
>> >
>> >Or maybe not. I could be all wet. The question I have for my own
>> >scenario is why doesn't the derailleur protect the PowerLink from
>> >the bullwhip like wave coming through the chain? Could the
>> >derailleur get flung back into the PowerLink and snap it open?
>>
>> Dear Tim,
>>
>> I may be all wet, too, but I _think_ that a 48-tooth chainwheel
>> advances exactly as far as a 12-tooth rear sprocket, half an inch.
>>
>> That is, the absolute distance is what matters, not the degrees of
>> rotation.
>
>Pondering that I think you may be correct. However, OTOH, I find that a
>skipping chain on a large sprocket is more noticeable through the feet
>than skipping on a small sprocket.
>
>> When the chain skips on the rear, it does so by each link engaging
>> higher and higher on the rear teeth until all the links touching the
>> rear teeth are near the tips of the teeth--and then they all slip
>> over the top at once and skip into the next position.
>>
>> So the whole linear chain (which wraps around two sprockets and makes
>> a Z-bend through the derailleur pulleys) skips forward half an inch.
>> It doesn't matter whether the chain is motionless or doing its feeble
>> 1.5 to 2.5 mph at 60 to 90 rpm--the skip speed is relative to
>> whatever the current speed is.
>
>When the chain skips, what is the effective rpm during that moment of
>free acceleration? The chain skip is most likely to occur with the
>leading leg at roughly 2:00-4:00, facing the chainring, which is the
>highest range of force from either the muscles or the weight of the
>rider on the pedal. Could the effective rpm for that brief moment be,
>say 200 rpm instead of 90? That would change the picture a bit.
>
>> Here's a diagram just to remind us of the chain path:
>>
>> http://i9.tinypic.com/4v38hhl.jpg
>>
>> Once the chain jumps into the new position, the links hitting the
>> teeth stop dead relative to their skip speed. But the links just
>> behind them, the short section feeding onto the rear sprocket, are
>> loose in that they swing from the spring-loaded double-arm of the
>> derailleur.
>>
>> So Jobst's idea is that the short length of chain on the rear
>> derailleur sped up, too, when the skip started, and is free to crash
>> into the "stopped" links that have re-engaged the 13-tooth. If the
>> quick-link is just short of the rear cluster, then the short lengh of
>> chain behind it will still be going faster, might bang into it, and
>> could compress and separate the two half links.
>>
>> The question for his theory is how fast the does a chain actually go
>> relative to its original speed? Since the distance involved is only
>> half an inch, we need an impressive acceleration to bang things
>> together. He's certain that it's plenty fast enough. I'm still
>> looking for evidence.
>
>Again, you are thinking about chain velocity as the product of pedaling
>speed 60-90 rpm. But what if, for that brief time interval, the
>effective rpm was 200 rpm? Or what if the energy traveling through the
>chain was not simply the linear velocity of the chain as pedaled but a
>whip-crack of energy being snapped through the chain? Could there be an
>addition of stored energy in the frame that is released into the chain?
>
>> Your idea about a reflected shock wave may well work, too, though I
>> have no idea what the details would be.
>>
>> As for the spring-loaded derailleur going boing! and somehow jamming
>> the quick-connect half-links together, that seems like a possibility,
>> particularly if the chain skip occurs just when the bike hits a bump.
>>
>> Jobst's explanation seems plausible to me, but only if we get a lot
>> of speed in half an inch of skip. Other explanations are also
>> plausible--a defective link, a good link not quite fitting completely
>> together, or a chain jam that hid itself by compressing the link and
>> then falling off.
>>
>> Whatever happened, it seems to be so rare that it's going to be
>> interesting to explain.
>>
>> It's so hard to duplicate the actual event that we can only advance
>> theories and perform what may be only faintly related experiments,
>> but we can still learn a lot even if we never agree about the
>> explanation.
>>
>> Cheers,
>>
>> Carl Fogel
Dear Tim,
Yes, the speed question is tricky.
When the chain skips, it may just accelerate at a speed equal to the
momentary rate of the rider's feet on the pedals. That is, the chain
is being tugged forward by the pedals.
This would probably be a trivial speed increase--the mass of your feet
and legs just doesn't accelerate very fast under muscle power in the
distance involved. For a 53-tooth and 175 mm crank, the pedal moves
about 20 mm (~ 4/5 inch) when the chain moves about 13 mm (~ 1/2
inch). The chain actually moves slower than the foot.
But the chain is under tension, so force is stored spring-style in the
muscles (I think) and the elastic frame and maybe in the chain. The
frame is certainly bent a little, like a huge leaf spring. The muscles
in one leg are straining against the pedal. And the upper chain,
though complicated and full of little interfaces, has to be under
tension--I don't know how efficiently the hundreds of pieces of tiny
parts in the upper chain run go boing! compared to the simple stiff
frame.
Here's a table of results for constant accelerations (not necessarily
the case with a chain skip--it may be coasting for a quarter-inch) for
milliseconds and half-inch distances, with the ratio of impact
(kinetic energy):
ke
avg final final ratio
speed speed accel speed of
ms fps fps f/s^2 mph impact
0.001 41.667 83.333 83,333.33 56.8 3226.8
0.002 20.833 41.667 20,833.33 28.4 806.6
0.005 8.333 16.667 3,333.33 11.5 132.3
0.010 4.167 8.333 833.33 5.7 32.5
0.020 2.083 4.167 208.33 2.8 7.8
0.040 1.042 2.083 52.08 1.4 2.0
0.051 0.817 1.634 32.04* 0.8 0.6
*free fall = 32 f/s^2
With a rubber band, you can fling a couple of chain links about 50
feet in about a second, as I did down my driveway. The links
accelerate to about 50 fps in about 2 inches of rubber-band travel and
then coast with very little speed loss until they hit the driveway.
The figures are _very_ rough, but that puts the rubber band impact
somewhere near the top of the scale above, where the final speed is 41
to 83 fps.
As I explained at far too much length, I doubt that the chain skip
speed is at the bottom of the scale at free fall.
But I don't know how far up the scale it goes.
Kinetic energy is what will compress the two half-links, and it
increases with the square of velocity, so the differences between each
step are very large.
So the question is still how much the chain accelerates in half an
inch in that brief moment. If a brief moment is 0.001 seconds, then
the impact on the perfectly placed quick-connect is about twenty times
larger than if a brief moment is 0.005 seconds. That's why I'm not
sure if the rubber band test is realistic.
Cheers,
Carl Fogel
|
| | | | | | |
Date: 29 Jun 2007 16:52:44
From:
Subject: Re: Safe to lengthen a chain?
|
Tim McNamara writes:
> The question I have for my own scenario is why doesn't the
> derailleur protect the PowerLink from the bullwhip like wave coming
> through the chain? Could the derailleur get flung back into the
> PowerLink and snap it open?
I think you analyzed the action well but why stop there. When the
chain skips forward the derailleur must give chain. The rest of the
chain on the slack run doesn't even know of the incident yet and hangs
as always. That means, the treadle of the derailleur rotates to yield
more chain, both for the one link advance and for the chain rising
over the top of sprocket teeth.
When the chain falls back into engagement, the treadle, with its idler
wheels, does not snap back fast enough to tension the chain. The
hovering chain rams against an essentially stopped sprocket. That is
why I suggested a short length of chain and a rubber band.
Jobst Brandt
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