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Main
Date: 01 Jul 2007 02:00:21
From:
Subject: Chain skip
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Chain skip := chain advances one tooth under load on a sprocket and
re-engages with a sharp report.
Chain skip is a problem not only for those who ride in dirty terrain
but primarily for riders who replace their chains to achieve better
shifting and preventing undue wear on chainwheels and sprockets. A
worn chain can bend laterally more easily than a new one and,
therefor, tends to shift to an adjacent sprocket less easily, being
able to make a zig zag path. Just the same, the most used sprockets
of the gear cluster often skip when a new chain is installed and must
be replaced with new ones. This is the classic chain skip that occurs
mainly when pedaling hard.
On road bicycles a chain can be ridden until it is so out of pitch
that it doesn't show on a ruler. The method of testing is to hold a
ruler along the side of the chain aligning an inch mark with the
center of a link pin and noting how far off the inch mark the pin a
foot farther down the chain lies. Most bicycle chains are 1/2" pitch
and, therefore, one foot of chain has 24 link pins. Being off by 1/8"
or 0.125" is approximately 1% of 12" and that is probably the outer
limit of wear one should allow before replacing a chain.
In this assessment, the 1% wear is actually 2% because only half the
links are affected by pin-and-sleeve wear, the effect being measured.
Therefore the pitch error occurs once per inch of chain in spite of
there being 24 pins. Inner links, the ones in which the rollers are
held, do not change length.
If chain wear is greater than 4% then the half inch mark a foot
farther down the chain will be right on the mark and obscure that
there is enormous wear. Riders have believed that their chain doesn't
wear because they were 1/2 inch off per foot. Of course when a new
chain was installed, it skipped with even slight pedal force in most
gears.
Skipping is caused by wear pockets made by a worn chain. A chain that
has a larger pitch than the one for which the sprocket was designed
will not mesh properly. Therefore, as the chain wears and increases
its pitch, it climbs up the face of sprocket teeth and concentrates
all its load on a larger contact pitch diameter. A new chain, in
contrast, lands its rollers on the sprocket base circle and bears on
all the teeth at their base.
A new (in-pitch) chain may fit on a worn sprocket but under forward
pull on the sprocket, the chain roller that bears the load, the last
one to engage the sprocket, engages the wear pocket of the old
elongated pitch chain (a point that is behind the engagement it would
have at the base circle) so the next link of the chain cannot engage
the following tooth because it is already behind the following tooth
corner that prevents entry. The result is that all successive links
also fail to engage and when the leading engaged link disengages the
sprocket the chain skips ahead.
So much for new chains on old driven sprockets.
Driving sprockets, on the other hand, are forcefully engaged, the
incoming chain being under high tension from pedaling. Idling
presents no problem because the chain can fall to the base circle,
having no preferred spot on the teeth. That a worn (elongated) chain
rides high on sprocket teeth under load is visible by observing that
there is light between the chain and chainwheel's base circle even
when light pedaling.
A new chain on such a chainwheel, rides on the base circle because
already engaged links force it to do so. Therefore, there is no skip
with a new chain. If a chain is allowed to run long enough to have
substantial wear, it can ride high enough on a chainwheel that hard
pedaling rounds off tooth tips and causes slip-skip, essentially a
continuous riding over the tops of chainwheel teeth, these generally
being aluminum that is readily deformed when chain load is
concentrated on a small area.
Faces of chainwheel teeth are often flared to both sides when their
teeth become narrow from running in skewed chain lines. That way an
out of pitch chain loads primarily one tooth and that tooth yields.
The smaller the chainwheel the faster it wears its fewer teeth and the
sooner an out of pitch chain can cause it to skip. However this does
not occur with 1% wear but with greater chain elongation or abrasive
chainwheel wear, and effect seen mainly from riding on gritty dirt,
especially mud.
Jobst Brandt
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Date: 01 Jul 2007 11:48:12
From: Ron Hardin
Subject: Re: Chain skip
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I agree with the analysis.
Add to the failure modes, on the chainwheel, that the chain pops off
the chainwheel entirely on a hard start, indicating it's time to
replace the chainwheel, the teeth having been worn down too far.
It used to be, in the 70s, that a chain would develop the rear-cog
skip after long use, indicating either that sprockets wore faster
than chains back then, or that it was the result of my using
chiefly the smallest cog back in my youth and so I simply wore that
one out fast with heavy pedalling, which I preferred to spinning.
Also, sometimes a new chain would skip on a new cog, but got over
it in a few hundred miles. I have no idea what caused that.
A bigger problem was always the Huret Alvit derailleur, which was
always instantly gunked up and failing to shift back onto the smallest
cog. The Sun Tour parallogram (also handy for driving tent pegs)
solved that, in the later 70s.
My own chain preference is to leave the chain on until it simply
no longer works, this being some problem on the chainwheel side,
and then put on new chain and freewheel, and possibly chainwheel
if the new chain doesn't work on it. I get about 4-6k miles on
a chain, I guess. If it still works, don't mess with it, is my
rule.
--
Ron Hardin
rhhardin@mindspring.com
On the internet, nobody knows you're a jerk.
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Date: 01 Jul 2007 00:18:05
From: Troll Report
Subject: Re: Chain skip
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On 01 Jul 2007 02:00:21 GMT, jobst.brandt@stanfordalumni.org wrote:
> [snip] Being off by 1/8"
> or 0.125" is approximately 1% of 12" and that is probably the outer
> limit of wear one should allow before replacing a chain.
>
> In this assessment, the 1% wear is actually 2% because only half the
> links are affected by pin-and-sleeve wear, [snip]
You say 1% wear is the outer limit one should allow, then you say 1% wear
is actually 2% wear. So doy ou mean to say .5% wear is the actuall outer
limit, and if so why don't you say so in the first place? Your writing is
confused and muddled, as if you are smoking crack.
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Date: 01 Jul 2007 17:34:43
From: John Henderson
Subject: Re: Chain skip
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Troll Report wrote:
> On 01 Jul 2007 02:00:21 GMT, jobst.brandt@stanfordalumni.org
> wrote:
>
>> [snip] Being off by 1/8"
>> or 0.125" is approximately 1% of 12" and that is probably the
>> outer limit of wear one should allow before replacing a
>> chain.
>>
>> In this assessment, the 1% wear is actually 2% because only
>> half the links are affected by pin-and-sleeve wear, [snip]
>
> You say 1% wear is the outer limit one should allow, then you
> say 1% wear is actually 2% wear. So doy ou mean to say .5%
> wear is the actuall outer limit, and if so why don't you say
> so in the first place? Your writing is confused and muddled,
> as if you are smoking crack.
My comprehension must be confused and muddled too, because I
thought Jobst expressed himself clearly.
John
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Date: 01 Jul 2007 22:35:03
From: Troll Report
Subject: Re: Chain skip
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On Sun, 01 Jul 2007 17:34:43 +1000, John Henderson wrote:
> Troll Report wrote:
>
>> On 01 Jul 2007 02:00:21 GMT, jobst.brandt@stanfordalumni.org
>> wrote:
>>
>>> [snip] Being off by 1/8"
>>> or 0.125" is approximately 1% of 12" and that is probably the
>>> outer limit of wear one should allow before replacing a
>>> chain.
>>>
>>> In this assessment, the 1% wear is actually 2% because only
>>> half the links are affected by pin-and-sleeve wear, [snip]
>>
>> You say 1% wear is the outer limit one should allow, then you
>> say 1% wear is actually 2% wear. So doy ou mean to say .5%
>> wear is the actuall outer limit, and if so why don't you say
>> so in the first place? Your writing is confused and muddled,
>> as if you are smoking crack.
>
> My comprehension must be confused and muddled too [snip]
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Date: 30 Jun 2007 20:51:07
From: Bill Sornson
Subject: Re: Chain skip
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jobst.brandt@stanfordalumni.org wrote:
> Chain skip := chain advances one tooth under load on a sprocket and
> re-engages with a sharp report.
A) Heard you the first time (one of many double posts from you lately); and
B) you're still wrong about worn chain rings (wheels) skipping with a new
chain. (See previous discussion, futile as that may be.)
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Date: 30 Jun 2007 23:26:09
From: Tim McNamara
Subject: Re: Chain skip
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In article <468724af$0$4866$4c368faf@roadrunner.com >,
"Bill Sornson" <askme@ask.me > wrote:
> jobst.brandt@stanfordalumni.org wrote:
> > Chain skip := chain advances one tooth under load on a sprocket and
> > re-engages with a sharp report.
>
> A) Heard you the first time (one of many double posts from you
> lately); and
That's odd, I have not seen double posts from Jobst or anyone else. Are
you only seeing them from Jobst or from others too? If the latter,
there may be a server issue.
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Date: 01 Jul 2007 07:34:11
From: Leo Lichtman
Subject: Re: Chain skip
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"Tim McNamara" wrote: (clip) Are you only seeing them from Jobst or from
others too? (clip)
^^^^^^^^^^^^^^^^
It came as a double post here also.
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Date: 01 Jul 2007 13:39:22
From:
Subject: Re: Chain skip
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On Sun, 01 Jul 2007 07:34:11 GMT, "Leo Lichtman"
<l.lichtman@worldnet.att.net > wrote:
>
>"Tim McNamara" wrote: (clip) Are you only seeing them from Jobst or from
>others too? (clip)
>^^^^^^^^^^^^^^^^
>It came as a double post here also.
Dear Tim & Leo,
Here, too, and on Google Groups.
Jobst's doubled posts are four minutes apart. The second one changes
"a larger pitch then" to "a larger pitch than"--it's a correction.
After sending a post, some people sit back and re-read their deathless
prose.
When they spot an error, they slap their foreheads, kill the original
post on their news server, and post the edited version.
Their server applies the kill, removes the offending original post,
and shows only the single corrected post, so the conscientious posters
are able to go to bed and sleep the sleep of the just.
But other servers ignore the kill, so the rest of us see both posts.
Cheers,
Carl Fogel
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Date: 02 Jul 2007 06:24:48
From: John Henderson
Subject: Re: Chain skip
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carlfogel@comcast.net wrote:
> After sending a post, some people sit back and re-read their
> deathless prose.
And isn't it odd that no amount of proof-reading seems to
eliminate all the errors? But the instant they're posted,
those errors suddenly turn visible, and stare back at you
mockingly.
John
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Date: 02 Jul 2007 09:21:18
From: Tim McNamara
Subject: Re: Chain skip
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In article <5eqgshF38pgftU1@mid.individual.net >,
John Henderson <jhenRemoveThis@talk21.com > wrote:
> carlfogel@comcast.net wrote:
>
> > After sending a post, some people sit back and re-read their
> > deathless prose.
>
> And isn't it odd that no amount of proof-reading seems to eliminate
> all the errors? But the instant they're posted, those errors
> suddenly turn visible, and stare back at you mockingly.
Especially in posts that criticize the spelling or grammar in another
post. Those always have spelling or grammatical errors.
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Date: 01 Jul 2007 00:33:12
From: Bill Sornson
Subject: Re: Chain skip
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Tim McNamara wrote:
> In article <468724af$0$4866$4c368faf@roadrunner.com>,
> "Bill Sornson" <askme@ask.me> wrote:
>
>> jobst.brandt@stanfordalumni.org wrote:
>>> Chain skip := chain advances one tooth under load on a sprocket and
>>> re-engages with a sharp report.
>>
>> A) Heard you the first time (one of many double posts from you
>> lately); and
>
> That's odd, I have not seen double posts from Jobst or anyone else.
> Are you only seeing them from Jobst or from others too? If the
> latter, there may be a server issue.
Just from Jobst. I'd guess there have been 10-12 double posts in the last
three days or so.
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Date: 01 Jul 2007 09:06:55
From: Tim McNamara
Subject: Re: Chain skip
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In article <468758be$0$12167$4c368faf@roadrunner.com >,
"Bill Sornson" <askme@ask.me > wrote:
> Tim McNamara wrote:
> > In article <468724af$0$4866$4c368faf@roadrunner.com>, "Bill
> > Sornson" <askme@ask.me> wrote:
> >
> >> jobst.brandt@stanfordalumni.org wrote:
> >>> Chain skip := chain advances one tooth under load on a sprocket
> >>> and re-engages with a sharp report.
> >>
> >> A) Heard you the first time (one of many double posts from you
> >> lately); and
> >
> > That's odd, I have not seen double posts from Jobst or anyone else.
> > Are you only seeing them from Jobst or from others too? If the
> > latter, there may be a server issue.
>
> Just from Jobst. I'd guess there have been 10-12 double posts in the
> last three days or so.
Weird. I have not seen any double posts, as I said, from Jobst or
anyone else (not in this newsgroup, that is; I've seen some doubles
elsewhere). Usenet is a strange beast at times.
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