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Main
Date: 22 Jul 2007 20:52:02
From: velodancer
Subject: Lowest possible gears continued
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The original thread appears to be closed. I didn't know that could
happen but I thought the thread still had not settled the point. So
here goes:
On Apr 19, 1:42 pm, carlfo...@comcast.net wrote:
> How does pushing pedals 1 meter around a 350mm diameter circle lower
> the required force to move the rear tire 1 meter compared to walking?
> Let us know if you work out an explanation that you could present to a
> high-school physics class that explains why moving your feet in a
> 14-inch high circle while crouching is more efficient than moving them
> the same distance while walking.
Because there is a wheel and gears!
Carl, you have written too much stuff in this very long thread to
refute point by point, but it is amazing so many have let you get away
with it. The invention of the wheel was a pivotal point in human
industry and I've never heard that utilizing a wheel made anything
less efficient on a relatively smooth rolling surface. Gears only
optimize discrepancies between the engine efficiencies and the work
required. Together wheels and gears blow walking away.
Walking is inherently less efficient under most circumstances. If you
must have some of the reasons explained, picture this: With every step
you take, you are raising and lowering your body mass. Some of this
energy loss is recovered in the elastic properties of ligaments and
tendons but it is still a net loss that you do not have with a
bicycle.
Why would you think that at some certain speed or workload that this
inefficiency would magically disappear? Why do you think that this
circle you keep describing is inefficient at a low forward velocity
but efficient at a high forward velocity? Common sense will tell you
otherwise.
But enough of the big picture. I have extensive experience (about two
years of full time loaded touring so far) going up hills with a loaded
touring bike at 2 miles an hour (balance becomes difficult at 1.5 mph
and less). It is ALWAYS harder to push the bike rather than ride. The
primary reason that I ever push a bike up a hill is because of loss of
traction due to either a loose dirt or gravel surface. My speed drops
when I dismount and have to push as well as my perceived workload. The
minute I am able, I remount.
Most of my bikes have had a 19 inch low gear. I recently dropped down
to a 15 inch low gear. This made a ton of difference, even on an
unloaded bicycle. In large part because I am able to increase my
cadence on very steep hills, reducing the dead stop of forward
momentum at the top and bottom of my pedal stroke. This reduces the
very noticeable torque on my knees powering through the dead spot at
lower cadence.
Additionally, I noticed on my first dirt trial that I was able to
clean some short (20 feet), very steep sections in the 15 in low gear
that I was unable to clean in the 19 inch low gear. This is because my
smoother stroke at a higher cadence (same speed, as slow as I could
manage) did not break the rear tire loose every time I reached TDC on
the pedals. This was on a smooth tired bike with 18 inch chainstays
where such effects are more easily discerned than a knobby tired bike
with sub 17 inch chainstays.
Anyway, get real! I'll have to assume you have a bad case of cognitive
dissonance. These are the facts of wheels and gears, backed up by
experience.
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Date: 23 Jul 2007 19:01:26
From: velodancer
Subject: Re: Lowest possible gears continued
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On Jul 23, 3:46 pm, carlfo...@comcast.net wrote:
> Give us the necessary details to evaluate your claim for increased
> efficiency.
Let me summarize again:
1. Wheels (which efficiently conserve forward momentum vs none for
walking)
2. Gears (for best match of terrain and engine vs one "gear" only for
walkers)
3. Weight supported (vs walker must constantly support own weight and
even move it up and down for walking to happen - even flat footed
walking)
Billions of studies confirming the efficiency of the wheel. Hundreds
of measurements of the efficiency of bicycling versus just about
anything else on calories burned per unit distance.
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Date: 23 Jul 2007 20:49:04
From:
Subject: Re: Lowest possible gears continued
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On Mon, 23 Jul 2007 19:01:26 -0700, velodancer <commerce48@yahoo.com >
wrote:
>On Jul 23, 3:46 pm, carlfo...@comcast.net wrote:
>
>> Give us the necessary details to evaluate your claim for increased
>> efficiency.
>
>Let me summarize again:
>
>1. Wheels (which efficiently conserve forward momentum vs none for
>walking)
>2. Gears (for best match of terrain and engine vs one "gear" only for
>walkers)
>3. Weight supported (vs walker must constantly support own weight and
>even move it up and down for walking to happen - even flat footed
>walking)
>
>Billions of studies confirming the efficiency of the wheel. Hundreds
>of measurements of the efficiency of bicycling versus just about
>anything else on calories burned per unit distance.
Dear VD,
Again, you miss the point of the thread--grades and loads steep enough
to require severe gearing have little to do with ordinary riding.
1) How much "momentum" do you think you're getting at under 2 mph from
a pair of bicycle wheels? How far up the hill do you coast? Do you
think that the wheels stop turning when you get off and push?
2) Walking offers an infinitely wider range of "gearing" on a severe
slope than any bicycle--you just change your stride and pace. You can
hardly hope to shift gears on such slopes on a bike, and you have
enormous trouble getting started again if you stop pushing past the
dead spots.
3) Again, you don't lower your weight as you climb a severe grade.
4) No studies, much less billions, show pedaling a bicycle up a severe
grade--so severe that you need 1-to-1 gearing to get up it--is more
efficient. If such studies exist, please cite just one.
Obviously, we're not getting anywhere.
I'll gladly change my mind and agree that pushing a bike up such
severe grades is much less efficient than riding up with any gearing
that you choose, just as soon as you convince the Fargo Street Hill
Climb contestants that it would be much harder to push their bikes to
the top:
http://www.lawheelmen.org/fargo.htm
Those who can't pedal straight to the top usually start tacking from
side to side to reduce the grade, something pedestrians rarely bother
with--they just shorten their stride and lower their pace in the
natural fashion.
Those riders who can't pedal to the top of Fargo Street usually get
off and push the rest of the way, being determined to get there one
way or another.
Their collective experience is probably more credible than the
isolated anecdotes we see here on RBT.
I don't see a list honoring the spectators who walked up the Fargo
Street hill. In fact, I doubt that even a Boy Scout troop would give
awards for hiking to the top of Fargo Street with a 20-pound pack.
But maybe next year some competitors will start pushing to the top,
just to show how strong they are.
:)
http://www.lawheelmen.org/fargo.htm
http://www.pbase.com/coaster/fargo_street_hillclimb_2007
Cheers,
Carl Fogel
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Date: 24 Jul 2007 05:12:12
From: Michael Press
Subject: Re: Lowest possible gears continued
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In article
<fuoaa3hm8hu60mqn03gt0ksirvdtthepeb@4ax.com >,
carlfogel@comcast.net wrote:
> 4) No studies, much less billions, show pedaling a bicycle up a severe
> grade--so severe that you need 1-to-1 gearing to get up it--is more
> efficient. If such studies exist, please cite just one.
More efficient than what?
--
Michael Press
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Date: 25 Jul 2007 11:44:06
From: Michael Press
Subject: Re: Lowest possible gears continued
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In article
<rubrum-50DC90.22121223072007@newsclstr02.news.prodigy.
com >,
Michael Press <rubrum@pacbell.net > wrote:
> In article
> <fuoaa3hm8hu60mqn03gt0ksirvdtthepeb@4ax.com>,
> carlfogel@comcast.net wrote:
>
> > 4) No studies, much less billions, show pedaling a bicycle up a severe
> > grade--so severe that you need 1-to-1 gearing to get up it--is more
> > efficient. If such studies exist, please cite just one.
>
> More efficient than what?
Carl, more efficient than what?
--
Michael Press
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Date: 23 Jul 2007 21:06:50
From:
Subject: Re: Lowest possible gears continued
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On Mon, 23 Jul 2007 20:49:04 -0600, carlfogel@comcast.net wrote:
>On Mon, 23 Jul 2007 19:01:26 -0700, velodancer <commerce48@yahoo.com>
>wrote:
>
>>On Jul 23, 3:46 pm, carlfo...@comcast.net wrote:
>>
>>> Give us the necessary details to evaluate your claim for increased
>>> efficiency.
>>
>>Let me summarize again:
>>
>>1. Wheels (which efficiently conserve forward momentum vs none for
>>walking)
>>2. Gears (for best match of terrain and engine vs one "gear" only for
>>walkers)
>>3. Weight supported (vs walker must constantly support own weight and
>>even move it up and down for walking to happen - even flat footed
>>walking)
>>
>>Billions of studies confirming the efficiency of the wheel. Hundreds
>>of measurements of the efficiency of bicycling versus just about
>>anything else on calories burned per unit distance.
>
>Dear VD,
>
>Again, you miss the point of the thread--grades and loads steep enough
>to require severe gearing have little to do with ordinary riding.
>
>1) How much "momentum" do you think you're getting at under 2 mph from
>a pair of bicycle wheels? How far up the hill do you coast? Do you
>think that the wheels stop turning when you get off and push?
>
>2) Walking offers an infinitely wider range of "gearing" on a severe
>slope than any bicycle--you just change your stride and pace. You can
>hardly hope to shift gears on such slopes on a bike, and you have
>enormous trouble getting started again if you stop pushing past the
>dead spots.
>
>3) Again, you don't lower your weight as you climb a severe grade.
>
>4) No studies, much less billions, show pedaling a bicycle up a severe
>grade--so severe that you need 1-to-1 gearing to get up it--is more
>efficient. If such studies exist, please cite just one.
>
>Obviously, we're not getting anywhere.
>
>I'll gladly change my mind and agree that pushing a bike up such
>severe grades is much less efficient than riding up with any gearing
>that you choose, just as soon as you convince the Fargo Street Hill
>Climb contestants that it would be much harder to push their bikes to
>the top:
>
>http://www.lawheelmen.org/fargo.htm
>
>Those who can't pedal straight to the top usually start tacking from
>side to side to reduce the grade, something pedestrians rarely bother
>with--they just shorten their stride and lower their pace in the
>natural fashion.
>
>Those riders who can't pedal to the top of Fargo Street usually get
>off and push the rest of the way, being determined to get there one
>way or another.
>
>Their collective experience is probably more credible than the
>isolated anecdotes we see here on RBT.
>
>I don't see a list honoring the spectators who walked up the Fargo
>Street hill. In fact, I doubt that even a Boy Scout troop would give
>awards for hiking to the top of Fargo Street with a 20-pound pack.
>
>But maybe next year some competitors will start pushing to the top,
>just to show how strong they are.
>
> :)
>
>http://www.lawheelmen.org/fargo.htm
>
>http://www.pbase.com/coaster/fargo_street_hillclimb_2007
>
>Cheers,
>
>Carl Fogel
Oops, copied the same link twice instead of this one:
http://www.youtube.com/watch?v=d0mECFP76vA
Valiant effort, tacking fails, rider seems to push up the last part.
Pedestrians visible walking casually up the street through most of the
video, which gets much less jerky toward the end. I bet the rider got
further up the hill than I would.
CF
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Date: 23 Jul 2007 13:24:50
From: peter
Subject: Re: Lowest possible gears continued
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On Jul 23, 12:04 pm, carlfo...@comcast.net wrote:
> On Mon, 23 Jul 2007 09:12:34 -0700, velodancer <commerc...@yahoo.com>
> wrote:
>
> Dear VD,
>
> Again, what's your overall pedal movement to rear tire ratio?
>
> In other words, tell us what tire diameter, what crank length, and
> what sprockets you're using.
>
> If it doesn't work out to 1-to-1, your experience doesn't apply.
He's already given you the required information, assuming he measured
things correctly. He said his gearing is 15" and his cranks are
170mm, i.e. 170/25.4*2 = 13.4" for pedal circle diameter.
Therefore the ratio of pedal movement to rear tire is 1 to 1.12 or
pretty close to your requested 1 to 1.
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Date: 23 Jul 2007 16:29:21
From:
Subject: Re: Lowest possible gears continued
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On Mon, 23 Jul 2007 13:24:50 -0700, peter <prathman@comcast.net >
wrote:
>On Jul 23, 12:04 pm, carlfo...@comcast.net wrote:
>> On Mon, 23 Jul 2007 09:12:34 -0700, velodancer <commerc...@yahoo.com>
>> wrote:
>>
>> Dear VD,
>>
>> Again, what's your overall pedal movement to rear tire ratio?
>>
>> In other words, tell us what tire diameter, what crank length, and
>> what sprockets you're using.
>>
>> If it doesn't work out to 1-to-1, your experience doesn't apply.
>
>He's already given you the required information, assuming he measured
>things correctly. He said his gearing is 15" and his cranks are
>170mm, i.e. 170/25.4*2 = 13.4" for pedal circle diameter.
>Therefore the ratio of pedal movement to rear tire is 1 to 1.12 or
>pretty close to your requested 1 to 1.
Dear Pete,
When dealing with this particular thread, I learned long ago to ask
for specific information. Last time, I gave up in disgust when the
actual gearing in lengthy examples finally emerged.
Why on earth is it so hard to provide the specifics after all the
claims about the experience? It only reinforces the impression that
the poster is careless and unconcerned with mere details that get in
the way of his assertions.
If a 12% difference is "pretty close," then it doesn't matter whether
you use a 17 or a 19 on the rear--19/17 = 1.1176. Most riders find the
difference quite noticeable on grades.
Incidentally, are the figures for the trials bike in short sections
where momementum and wild spinning are the obvious factors, or for a
touring bike up a steady grade?
Cheers,
Carl Fogel
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Date: 23 Jul 2007 13:08:36
From: velodancer
Subject: Re: Lowest possible gears continued
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On Jul 23, 12:04 pm, carlfo...@comcast.net wrote:
> On Mon, 23 Jul 2007 09:12:34 -0700, velodancer <commerc...@yahoo.com>
> wrote:
>
> Dear VD,
>
> Again, what's your overall pedal movement to rear tire ratio?
>
> In other words, tell us what tire diameter, what crank length, and
> what sprockets you're using.
>
> If it doesn't work out to 1-to-1, your experience doesn't apply.
>
> If it does, we'll have some fun talking about cadence.
>
> Cheers,
>
> Carl Fogel
Why don't you answer any of my questions? What does cadence have to do
with relative efficiency of a wheeled vehicle versus walking?
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Date: 23 Jul 2007 16:46:07
From:
Subject: Re: Lowest possible gears continued
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On Mon, 23 Jul 2007 13:08:36 -0700, velodancer <commerce48@yahoo.com >
wrote:
>On Jul 23, 12:04 pm, carlfo...@comcast.net wrote:
>> On Mon, 23 Jul 2007 09:12:34 -0700, velodancer <commerc...@yahoo.com>
>> wrote:
>>
>> Dear VD,
>>
>> Again, what's your overall pedal movement to rear tire ratio?
>>
>> In other words, tell us what tire diameter, what crank length, and
>> what sprockets you're using.
>>
>> If it doesn't work out to 1-to-1, your experience doesn't apply.
>>
>> If it does, we'll have some fun talking about cadence.
>>
>> Cheers,
>>
>> Carl Fogel
>
>Why don't you answer any of my questions? What does cadence have to do
>with relative efficiency of a wheeled vehicle versus walking?
Dear VD,
Because I rarely swat at swarms of buzzing flies.
Give us the necessary details to evaluate your claim for increased
efficiency.
Show us that you understand that the topic--which you resurrected--was
whether it is more efficient to move up a steady grade by walking and
pushing a bicycle when the grade and load are so steep and heavy that
the rider is reduced to 1-to-1 overall gearing.
When you move your feet on the pedals just as the tire moves, what
advantage is gained in moving the load up the hill by running the
power through the drag of the chain and tires? You've lost the
mechanical advantage (leverage) that allows us to trade force for
distance when we do work.
Once you drop to 1-to-1 overall, you've lost the advantage that lets
people casually cruise faster than the fastest runners in the world on
the level. My 175 mm crank on a 53x11 coupled to a 2124 mm 700c tire
gives me an overall ratio of 9.307 to 1. Since I'm not lifting any
weight and have only chain, tire, and wind drag, I can stride nine
times as far as usual. Moving my foot once around the 1100 mm pedal
circle moves me over 33 feet.
But if the grade is steep enough that I can't pedal anything better
than 1-to-1 overall, then I move with no mechanical advantage over
ordinary walking, lose power to chain and tire drag, and must press
just as hard on the pedals as I do on the ground.
It doesn't help that I'm in the unnatural and inefficient position of
sitting on the seat and moving my feet through unnatural circles. If
you're not sure that the posture and motion are unnatural, consider
what sprinters and climbers do--they stand up to improve their hip
angle and heave the bike from side to side, effectively flattening the
pedal circle.
Cheers,
Carl Fogel
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Date: 24 Jul 2007 00:41:58
From: Clive George
Subject: Re: Lowest possible gears continued
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<carlfogel@comcast.net > wrote in message
news:4uaaa3tcoocu2lhufcl7cbttb5tkriigki@4ax.com...
> It doesn't help that I'm in the unnatural and inefficient position of
> sitting on the seat and moving my feet through unnatural circles. If
> you're not sure that the posture and motion are unnatural, consider
> what sprinters and climbers do--they stand up to improve their hip
> angle and heave the bike from side to side, effectively flattening the
> pedal circle.
And bringing other muscles into play, but I'm sure you only forgot to
mention that bit.
It's been pointed out to you before, but I'll remind you : your worries that
the riding position is less efficient than walking are unfounded. The reason
is that while walking, you have to push the bike as well. If your bike is at
all heavy (touring bike, tandem), that's not comfortable at all. It hurts
the calves in a way that walking without a bike doesn't. Add in the fact
that while riding a bike you're likely to not be wearing walking shoes, and
it starts to become obvious to all but you why people prefer to ride rather
than push.
But once again, you'll ignore these facts, which after all are only based on
actual experience. You'll carry on arguing about the number of teeth on a
sprocket and imaginary gearing (just how long do you think a stride is? You
do know it changes length significantly depending on what you're doing,
don't you?). In this thread you've demonstrated the most stunning level of
obtuseness and inability to consider anything which doesn't agree with your
pet theory - and TBH I have no idea why.
clive
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Date: 23 Jul 2007 11:19:39
From: velodancer
Subject: Re: Lowest possible gears continued
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On Jul 23, 7:54 am, carlfo...@comcast.net wrote:
> Possibly your whole post is based on that confusion. No one disputes
> that bicycles are more efficient on typical grades, where high overall
> pedal-to-tire-movement ratios can be sustained.
Actually, you are arguing just that!
> At a 1-to-1 pedal-to-rear-tire-movement overall ratio, your cadence is
> the same as the pace of a hiker pushing a bike up the same steep grade
> next to you. How does adding the transmission losses of a chain and
> sprockets, the rolling resistance of a pair of heavily loaded tires,
> and the mechanical disadvantages of the dead spots in the pedal cycle
> increase efficiency? How does it help to raise and lower your legs in
> an unnatural circular motion?
And how do your arguments apply at the same gear and cadence, and
speed on flat ground? Your argument that this is less efficient on a
grade applies equally to flat ground. We all know that it is many
times more efficient on flat or grade.
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Date: 23 Jul 2007 09:16:44
From: velodancer
Subject: Re: Lowest possible gears continued
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On Jul 23, 8:51 am, cmcanulty <cmcanu...@gmail.com > wrote:
> I also think the lowest possible gear is easier on loaded climbs and
> keeping your cadence higher is easier on the knees.
20 tooth inner chainrings are readily available for compact triples.
There are adaptors to go lower, not sure how available they are these
days. The Mountain Drive is an available and popular option for some.
I ride a 406 wheeled bike (20 inch wheels), making obtaining low gears
quite easy.
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Date: 23 Jul 2007 09:12:34
From: velodancer
Subject: Re: Lowest possible gears continued
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On Jul 23, 7:54 am, carlfo...@comcast.net wrote:
> You do not, in fact, lower your body weight, as you walk _up_ a steep
> grade. You've confused walking on level ground (where this happens)
> with climbing (where it doesn't).
Walking involves moving your body weight up and down. The grade does
not matter, you cannot walk without doing that. A bicycle supports
your weight, the entire leg movement is much more efficiently
transfered into forward momentum.
> Possibly your whole post is based on that confusion. No one disputes
> that bicycles are more efficient on typical grades, where high overall
> pedal-to-tire-movement ratios can be sustained.
How does changing the relative road speed change the efficiency (air
resistance aside)?
> I argue that bicycles are less efficient than getting off and pushing
> when the grade demands that rider drop to 1-to-1 gearing for steady
> progress. Most of the fuss involved people who didn't realize that
> their grades and gearing weren't that steep.
You've clearly never tried that with a loaded touring bike.
> Let's move on to two other curious points in your post.
>
> First, how is it more efficient than walking to gear down and spin
> faster if you can only keep this up for short distances?
I never said that. I stated that I only dismount when traction does
not allow.
> Second, what is the actual overall gear ratio in your lengthy example?
> So what's your rear tire's effective circumference or rollout (what
> you put into a cyclocomputer), what's your crank length (probably
> something between 145 and 185 mm), and how many teeth are there on
> your front and rear sprockets?
Generally most cranks available for road use vary by only 5 mm. I'll
happily take a lecture on why that is important in the real world. As
it happens, my cranks are 170.
> Remember, the grade must be steep enough that you have to gear down to
> a 1-to-1 overall ratio just to pedal up it steadily. It's unlikely
> that you can even stop and start again on such a slope.
Thanks for the tips. Did you miss the part where I said I've toured
over two years? Yes, I try not to dismount as it can be hard to get
started again and then I may be stuck walking and pushing my bike
noticeably slower and with greater effort. Remounting on the steepest
slopes require either starting across the road instead of up it, or
holding onto a tree while both feet are placed on the pedals. Not sure
what starting has to do with rolling efficiency.
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Date: 23 Jul 2007 13:04:04
From:
Subject: Re: Lowest possible gears continued
|
On Mon, 23 Jul 2007 09:12:34 -0700, velodancer <commerce48@yahoo.com >
wrote:
Dear VD,
Again, what's your overall pedal movement to rear tire ratio?
In other words, tell us what tire diameter, what crank length, and
what sprockets you're using.
If it doesn't work out to 1-to-1, your experience doesn't apply.
If it does, we'll have some fun talking about cadence.
Cheers,
Carl Fogel
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Date: 23 Jul 2007 17:33:20
From: Clive George
Subject: Re: Lowest possible gears continued
|
"velodancer" <commerce48@yahoo.com > wrote in message
news:1185207154.996174.62530@e9g2000prf.googlegroups.com...
>> I argue that bicycles are less efficient than getting off and pushing
>> when the grade demands that rider drop to 1-to-1 gearing for steady
>> progress. Most of the fuss involved people who didn't realize that
>> their grades and gearing weren't that steep.
>
> You've clearly never tried that with a loaded touring bike.
He's not tried any of what he's talking about. His points are purely
hypothetical, and unlike in other threads he hasn't made even the slightest
effort at experiment to determine if his hypotheses have any basis in fact.
Carl - it's been said many times : go out and try it, don't just sit here
trying to argue.
clive
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Date: 23 Jul 2007 15:54:06
From: zencycle
Subject: Re: Lowest possible gears continued
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You're both horribly obfuscating the issue. Stick to the KISS method
(Keep It Simple, Stupid)
It _is_ simple. It comes down to momentum and resistance. A bicycle is
more efficient because it rolls. It experiences less resistance to the
force than walking, and yes, your body weight _is_ a factor. When you
pedal a bike, it starts moving forward. What's to stop it? resistance
from the air, tires, and gravity. When you _walk_ forward, the simple
act of putting your foot in front of you acts as a break, and energy
is required to:
a) overcome the braking action of the resistance of your foot on the
ground, and
b) support your body weight,
In a low gravity environment, the simple act of pushing off will keep
you moving when walking. The vector force of gravity will not have
nearly the effect of pulling your body mass _downward_. Translate that
to the bike. Your body weight is being supported. The resistance to
momentum therefore is, at low speeds, almost exclusively a function of
the rolling resistance of the bike. Rolling resistance is a function
of gravity vector. Moving more in a vector more parallel to the
gravity vector will more greatly enhance it's effect. In a cartesian
plot, moving in an x,y vector greatly increases rolling resistance,
while moving in an x, -y vector greatly reduces it. To take it one
'step' further, Sitting on a downhill will not necessarily
spontaneously start you moving in a downward direction, because your
legs, feet, and butt are acting as brakes. Sitting on a bike, roll
you will. Going up, the vector force of gravity on the ablity of the
bike to sustain forward momentum becomes increasing significant.
Resistance to the vector force of gravity. It _is_ that simple.
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Date: 23 Jul 2007 15:51:30
From: cmcanulty
Subject: Re: Lowest possible gears continued
|
I also think the lowest possible gear is easier on loaded climbs and
keeping your cadence higher is easier on the knees. How did you get a
15" gear? I currently run a 17" which is a 24 tooth front and a 34
tooth rear on a mountain bike with 26"X1.5" lightly treaded tires. It
s hard to even get that low except by modifying parts. Why does no one
ever sell a truly low geared bike? They keep adding number of gears
and thereby increasing the complexity and lowering tolerances yet
don't give a wider range of gears.
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Date: 22 Jul 2007 22:02:29
From: velodancer
Subject: Re: Lowest possible gears continued
|
> Dear VD,
>
> How do you lower your body mass as you walk up stairs?
>
> Cheers,
>
> Carl Fogel
Exhale? I don't know. What does that have to do with riding a bicycle
versus pushing a bicycle?
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Date: 23 Jul 2007 08:54:33
From:
Subject: Re: Lowest possible gears continued
|
On Sun, 22 Jul 2007 22:02:29 -0700, velodancer <commerce48@yahoo.com >
wrote:
>> Dear VD,
>>
>> How do you lower your body mass as you walk up stairs?
>>
>> Cheers,
>>
>> Carl Fogel
>
>Exhale? I don't know. What does that have to do with riding a bicycle
>versus pushing a bicycle?
Dear VD,
If your answer to such a simple question is that you don't know, your
explanation won't fly in the high school physics class. You were the
one who stated that raising and lowering your body mass somehow made
walking uphill inefficient.
You do not, in fact, lower your body weight, as you walk _up_ a steep
grade. You've confused walking on level ground (where this happens)
with climbing (where it doesn't).
Possibly your whole post is based on that confusion. No one disputes
that bicycles are more efficient on typical grades, where high overall
pedal-to-tire-movement ratios can be sustained.
I argue that bicycles are less efficient than getting off and pushing
when the grade demands that rider drop to 1-to-1 gearing for steady
progress. Most of the fuss involved people who didn't realize that
their grades and gearing weren't that steep.
Let's move on to two other curious points in your post.
First, how is it more efficient than walking to gear down and spin
faster if you can only keep this up for short distances? You can walk
for ten minutes up any grade that you can pedal a bicycle steadily.
You seem to be confusing maximum speed, momentum, and effort with
efficiency.
Second, what is the actual overall gear ratio in your lengthy example?
Neither 15 gear-inches nor 19 gear-inches tells us this--gear-inches
is just an unknown wheel diameter times the ratio of the front to the
rear sprocket, completely ignoring the crank length.
Gear inches are useful for comparing road bikes with faintly standard
tire sizes and cranks. It's only slightly better than saying 53x11,
which means one thing if we assume a 700c tire and 175 mm cranks, but
quite another thing for bikes with smaller tires or shorter cranks.
So what's your rear tire's effective circumference or rollout (what
you put into a cyclocomputer), what's your crank length (probably
something between 145 and 185 mm), and how many teeth are there on
your front and rear sprockets?
I'll be glad to explain how those details determine your overall
pedal-to-tire ratio and what it is, but it would be nice to know if
you're even using the 1-to-1 overall ratio that was the subject of the
original thread--some of the most vehement posters turned out to be
unaware that their gearing was far from a 1-to-1 overall ratio.
At a 1-to-1 pedal-to-rear-tire-movement overall ratio, your cadence is
the same as the pace of a hiker pushing a bike up the same steep grade
next to you. How does adding the transmission losses of a chain and
sprockets, the rolling resistance of a pair of heavily loaded tires,
and the mechanical disadvantages of the dead spots in the pedal cycle
increase efficiency? How does it help to raise and lower your legs in
an unnatural circular motion?
Remember, the grade must be steep enough that you have to gear down to
a 1-to-1 overall ratio just to pedal up it steadily. It's unlikely
that you can even stop and start again on such a slope.
Cheers,
Carl Fogel
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Date: 22 Jul 2007 22:05:41
From:
Subject: Re: Lowest possible gears continued
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On Sun, 22 Jul 2007 20:52:02 -0700, velodancer <commerce48@yahoo.com >
wrote:
>The original thread appears to be closed. I didn't know that could
>happen but I thought the thread still had not settled the point. So
>here goes:
>
>On Apr 19, 1:42 pm, carlfo...@comcast.net wrote:
>
>> How does pushing pedals 1 meter around a 350mm diameter circle lower
>> the required force to move the rear tire 1 meter compared to walking?
>
>> Let us know if you work out an explanation that you could present to a
>> high-school physics class that explains why moving your feet in a
>> 14-inch high circle while crouching is more efficient than moving them
>> the same distance while walking.
>
>Because there is a wheel and gears!
>
>Carl, you have written too much stuff in this very long thread to
>refute point by point, but it is amazing so many have let you get away
>with it. The invention of the wheel was a pivotal point in human
>industry and I've never heard that utilizing a wheel made anything
>less efficient on a relatively smooth rolling surface. Gears only
>optimize discrepancies between the engine efficiencies and the work
>required. Together wheels and gears blow walking away.
>
>Walking is inherently less efficient under most circumstances. If you
>must have some of the reasons explained, picture this: With every step
>you take, you are raising and lowering your body mass.
[snip]
Dear VD,
How do you lower your body mass as you walk up stairs?
Cheers,
Carl Fogel
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Date: 23 Jul 2007 21:15:34
From: velodancer
Subject: Re: Lowest possible gears continued
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On Jul 23, 7:49 pm, carlfo...@comcast.net wrote:
> Again, you miss the point of the thread--grades and loads steep enough
> to require severe gearing have little to do with ordinary riding.
Perhaps we should install legs on automobiles so they can be more
efficient going up hills! In general, this is not the usual
engineering solution to any transport problem, almost all will use
wheels. Why? There is nothing more efficient.
> 3) Again, you don't lower your weight as you climb a severe grade.
Pushing off with your foot is required for walking. About the only
thing that changes with a steep grade is that there is no longer a
heel strike. At all times you are supporting your weight with muscles
doing work and burning calories. Seated cycling is fully weight
supported with proper gearing.
> 4) No studies, much less billions, show pedaling a bicycle up a severe
> grade--so severe that you need 1-to-1 gearing to get up it--is more
> efficient. If such studies exist, please cite just one.
Not necessary to have one just for your one to one gearing example
(what on earth difference does 1 to 1 gearing make? - my low gear is
lower than that). Perhaps you can quote just one study supporting your
rather outrageous and unsupported position.
> Those who can't pedal straight to the top usually start tacking from
> side to side to reduce the grade, something pedestrians rarely bother
> with--they just shorten their stride and lower their pace in the
> natural fashion.
>
> Those riders who can't pedal to the top of Fargo Street usually get
> off and push the rest of the way, being determined to get there one
> way or another.
>
> Their collective experience is probably more credible than the
> isolated anecdotes we see here on RBT.
Their gears are clearly not low enough. Tacking lowers the effective
grade and raises the useable gears.
Thus the argument for very low gears found on most motor vehicles but
for some reason not found on many bicycles. However, part of the issue
on such a steep hill is balance, a problem related to two wheels. I
don't think a properly geared tricycle would have any problem.
> I don't see a list honoring the spectators who walked up the Fargo
> Street hill. In fact, I doubt that even a Boy Scout troop would give
> awards for hiking to the top of Fargo Street with a 20-pound pack.
They are not attempting the difficult feat of balancing a two wheeler
on such a grade. Regardless of applause, that has nothing to do with
the efficiency question. You keep changing the subject. Which is how
to prove that under any normal riding situation, that walking is more
efficient than cycling. I maintain you can't do it and you don't
appear to be trying.
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