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crank length and climbing

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crank length and climbing

Old 01-20-06, 02:47 PM
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Originally Posted by Pico
The formula for a circumference of a circle is 2*pi*radius. The radius is not squared, you're probably thinking of the formula for the area of a circle.

Leverage tracks in a 1:1 ratio with crank length.
d'oh! well at least we now know how much more metal a big, solid, 175mm circular crank would require.
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Old 01-20-06, 05:56 PM
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Originally Posted by EURO
Pantani used 180's and was 5' 7"
and some drugs...
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Old 01-20-06, 07:44 PM
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Let me put this to rest. I can add more crank lengths if you guys want...

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Old 01-20-06, 07:50 PM
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Originally Posted by EdZ
Let me put this to rest. I can add more crank lengths if you guys want...

Yes, it is clear that a longer crank gives more leverage. The question is whether this translates into better climbing. Going up a hill that is too steep for the rider to maintain a reasonable cadence in any gear, would a slightly longer crank make the rider faster? Do riders generate the same force with different crank lengths? Do their force (or torque or power... doesn't really matter since they're correlated) vs. cadence curves look the same with different crank lengths? If not, how does crank length affect the cadence at which max torque is generated? What about max power?
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Old 01-20-06, 07:51 PM
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I'd change the gearing not the crank length. At the end of the day crank length should be about what suits you best from a biomechanical point of view, let the gears sort out the torque.
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Old 01-20-06, 10:39 PM
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Originally Posted by mingsta
I'd change the gearing not the crank length. At the end of the day crank length should be about what suits you best from a biomechanical point of view, let the gears sort out the torque.
+1, my thoughts exactly. Gears are for adjusting cadence, your crank length should suit you body.
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Old 01-21-06, 03:04 AM
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I've had 170mm to 180mm and all I can say is that this whole issue is over-rated.
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Old 01-21-06, 12:35 PM
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Originally Posted by simplyred
So... for a rec rider...
Attempting a mountainous ride with 170's/165's with a double 54/42 & 11-21 cassette is similar to jumping out of a plane without a chute?

-simplyred
Ouch. Can you say 50 rpm on your 165mm cranks and 42/21 climbing combo going up a 6% ascent?
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Old 01-21-06, 12:57 PM
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Thanks again for everyone's feedback. I definitely agree that crank size should not be used as a substitute for proper gearing. I'm not making any changes now, but in the future, when I determine proper crank length for the best fit, if two sizes fit me equally well, I'll probably go with the slightly longer crank to help with low(er) cadence climbing.

As for simplyred's post, I'll say that it's not like jumping out of a plane without a chute. Jumping out of the plane, you'll get where you want to go really fast. Geared with a 42/21 in the mountains, a recreational rider is going to take all day to get anywhere!
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Old 01-21-06, 01:29 PM
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Originally Posted by ggg300
and some drugs...
Which makes him different from which other riders?
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Old 01-21-06, 01:36 PM
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Originally Posted by EURO
Pantani used 180's and was 5' 7"
Pantani was also a drug cheat and died of cocaine induced heart failure. So you think its okay to emulate his crank length? If I extrapolate that (and I know how you like to extrapolate, ref: Euro's standard paedophile argument), I take it that you also condone his use of drugs in sport, right? RIGHT?!?!?!?
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Old 01-21-06, 03:18 PM
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Boys...lets stay on topic and deflect the drug discussion for a change. I was in experient mode this summer and sent an e-mail to Sheldon Brown for his advice. He said that a rider is no faster on longer cranks 0-5mm and a 2.5mm crank length change is virtually imperceptible. Have to report like the other guys...since I went from 175mm to 172.5mm thinking I could spin smoother at higher cadence...I lost power. So as other reported including Terry who may be the leading expert on climbing here...longer cranks do create more power for climbing...prefaced by...if they aren't too long. One of the very rare times I disagree with the bicycle expert Sheldon Brown based upon my experience...and don't thing long cranks are placebo either.
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Old 01-21-06, 04:26 PM
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Originally Posted by biker7
So as other reported including Terry who may be the leading expert on climbing here...longer cranks do create more power for climbing...prefaced by...if they aren't too long.
Just a minor correction: longer cranks produce more torque, but not necessarily more power. The limiting factor in steady state power production is almost always cardio-vascular.
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Old 01-21-06, 05:33 PM
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Originally Posted by terrymorse
Just a minor correction: longer cranks produce more torque, but not necessarily more power. The limiting factor in steady state power production is almost always cardio-vascular.
Sorry to correct you Terry but Power is proportional to Torque X RPM. So given any increase in torque due to longer cranks at any given cadence or RPM, Power increases proportionately.
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Old 01-21-06, 05:51 PM
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Terry is correct. As long as your gearing and crank length aren't ridiculous, only power:weight ratio really matters.

An overgeared rider with better W/kg can mash his way up a climb much faster than a less powerful rider with any crank length or gear ratio who is spinning beautifully.

Climbing is really much simpler than most people think. I've found that technique matters very little and one doesn't even have to do that much climbing to be good at it.
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Old 01-21-06, 06:16 PM
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Originally Posted by EURO
Which makes him different from which other riders?

Credit one pro and discredit another on the basis of alleged drug use…who would do that?
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Old 01-21-06, 06:24 PM
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Originally Posted by 53-11_alltheway
I've had 170mm to 180mm and all I can say is that this whole issue is over-rated.

wow...that is a lot coming from you...you were all over the idea...thanks for the input...that is something to note
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Old 01-21-06, 07:05 PM
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Originally Posted by biker7
Sorry to correct you Terry but Power is proportional to Torque X RPM. So given any increase in torque due to longer cranks at any given cadence or RPM, Power increases proportionately.
George
"at any given cadence" ... there's the rub. Your heart's the limiter of power, not leg strength or torque. If your heart can't supply the oxygen to the muscles, you can't maintain the cadence.

If you're at the limit aerobically, a longer crank won't let you produce any more power. Only more torque, but that's usually a good thing when climbing. More torque means a lower peak quad muscle output, reducing fatigue.
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Old 01-21-06, 07:32 PM
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Originally Posted by terrymorse
If you're at the limit aerobically, a longer crank won't let you produce any more power. Only more torque, but that's usually a good thing when climbing. More torque means a lower peak quad muscle output, reducing fatigue.
First two sentences, I follow you. Care to explain on that last sentence? I would have thought more max torque is good for the same max power when climbing because it lowers the optimal cadence range. And this may be a good thing when climbing since your speeds aren't as fast, so you have more useful gearing if your optimal cadence in your lowest gear is at a lower speed. I guess I don't understand how more torque translates into lower peak output in the quads.
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Old 01-21-06, 11:41 PM
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Originally Posted by jschen
Let me preface this by saying that I have no intention of changing any of my equipment at this time. This question is being asked more out of curiosity since random optimization problems are always on my mind. And perhaps it will help guide decisions on equipment at some point in the future.

Evidently, a shorter crank makes it easier to spin at high cadences. So does that mean a longer crank makes it easier to climb really steep stuff when you're running out of gears? Let's say you're on a steep climb, already in your lowest gear, and watching your cadence bog down. Presumably, since you get more leverage with a longer crank, you can generate more torque, and if you're out of gears and at a low cadence, more torque should equal more power. Argued from a slightly different angle, does a longer crank optimize for a slightly lower cadence, thus allowing you to take on a slightly steeper grade before your cadence starts bogging down?

So what do you think? For what it's worth, Sheldon Brown advocates calculating a "gain ratio" that takes into account crank length, and based on the numbers, he seems to advocate the belief that a longer crank equals slightly lower gearing. And I know Lance Armstrong went to a shorter crank to improve spin, but unlike him, us mere mortals do run out of gears. Since he's not running out of gears, I don't think the analysis I suggest above really applies to him or any other pro.

So what about us mortals? If you have a bike dedicated to very hilly rides (or if you always ride hilly stuff), would a slightly longer crank make sense? Of course, it's no substitute for proper gearing, but would it help you get past the occasional 15-20% pitch (or whatever "borderline too steep" means to you) in the road?
Lance Armstrong went to a shorter crank to improve spin
He usee 175s last year. Are you saying that he came down from 177.5s or 180s???
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Old 01-22-06, 12:23 AM
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Originally Posted by jschen
I definitely agree that crank size should not be used as a substitute for proper gearing.
That gets right to the point, yes. Boy, some people in this thread need to revisit their high school physics.
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Old 01-22-06, 02:16 AM
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It's not that big a deal to ride different crank lengths-- I've done it for years. You adjust almost instantly.

I ride 172.5 on the road. It's what came with the bike.

I ride 165 on the track-- I don't like long cranks on a steep track. I've tagged 165s on a 43 degree track without going down. I've seen people used to a shallow track show up on a steep one, bang their 170s on the banking, and go down.

I have 175 on the mountain bike - it's what came with the bike.

I ride the road bike at least 5 days a week, usually 6 or 7. I train and/or race at the track 2 days a week. A lot of times I'll do 60 miles in the morning on the road bike and then ~30 in the afternoon on the track bike. It's not a big deal to ride different length cranks.

I haven't been on the mountain bike for a while (too much road and track), but there have been times when I rode all three bikes in one day. It's not a big deal.

People worry way more about tiny things like crank length than they should. Just ride it and see how it feels.
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Old 01-22-06, 03:31 AM
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Originally Posted by terrymorse
"at any given cadence" ... there's the rub. Your heart's the limiter of power, not leg strength or torque. If your heart can't supply the oxygen to the muscles, you can't maintain the cadence.

If you're at the limit aerobically, a longer crank won't let you produce any more power. Only more torque, but that's usually a good thing when climbing. More torque means a lower peak quad muscle output, reducing fatigue.
It is only "a rub" if you limit your perspective to thinking of power in terms of your aerobic threshold... which is to deny a basic tenent of physics that is...power is proportionate to torque be it aerobic or anaerobic.
For those that want to understand the relationship between power and torque more fully which is pretty straight forward, here is a good article:
https://users.frii.com/katana/biketext.html
George
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Old 01-22-06, 03:45 AM
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Originally Posted by Squint
Climbing is really much simpler than most people think. I've found that technique matters very little and one doesn't even have to do that much climbing to be good at it.
ahh...the internet.
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Old 01-22-06, 10:56 AM
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Originally Posted by biker7
It is only "a rub" if you limit your perspective to thinking of power in terms of your aerobic threshold... which is to deny a basic tenent of physics that is...power is proportionate to torque be it aerobic or anaerobic.
I still think my perspective is the slaient one. Available power at a given aerobic effort, whether its 50% or 100%, won't be affected by gear selection or crank length. Those things make it easier or harder on your muscles, but sadly they won't do a thing for power.

As a wise person once said, "it's an aerobic sport, dammit!"
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