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I am looking at a new bike but it has 170 mm crankarms....is there pros or cons to shorter crankarms? I am just under 5'10 average inseam
With crankarms too long, you may hurt yourself and be less efficient, by throwing your hips around. With crankarms too short, there isn't a huge negative aspect, though you may have a less efficient stroke.

I think that "leverage" and "Gain ratio" arguments are dubious at best, because your will conter-balance the a mechanical advantage in the drivetrain.
 

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It's primarily a question of proper fit. Work with your shop - they should set up the bike with the proper size for you, and swap out the crankarms if necessary.

That being said, I am 5'11" and I have one bike with 170 and another with 172.5 and both seem fine to me. I even have a track bike with 165's. Track bikes typically have shorter cranks to reduce the chances of a pedal strike on the banking of a velodrome. On a road bike, shorter cranks would also reduce the likelihood of toe overlap.
 

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I am looking at a new bike but it has 170 mm crankarms....is there pros or cons to shorter crankarms? I am just under 5'10 average inseam
Throw caution to the wind. Go with 171.25. That's where the real sweet spot is.

Or you can read the actual research that shows no conclusions whatsoever about crank length and performance as a function of leg length or anything else. Shorter cranks do make it a little bit easier to spin. Other than that it is personal preference (and even that is based on belief, not facts).
 

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I bought a used bike with 175 and it felt fine, then I upgraded the cranks and on the advice of my shop went with 172.5 which was noticably better, more comfortable espcially at higher cadences. Got me thinking about 170. If there is any difference in leverage I certainly don't notice it.
 

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I go 175 on single speeds and 172.5 on everything else...

Why? because my first bike had 172.5 on it and I've followed suit. I think that you'll be hard pressed to find someone who just can't work with any/all of the "normal lengths"
 

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I'm 5'10 or so. Used 172.5, 175, 177.5, 182 & 185mm cranks. Have a set of nos record square taper in 180 to use when ready.
Coming from bmx on 180 to my 1st road bike with 172.5 I never really felt in the bike although I span them ok. With them I had spacers under the stem etc. For overall fitting.
Now I'm on the 177.5 cranks and have found a good fit with slamming the stem, being able to spin and apply the force I want.
Was pushing into a head wind with another guy yesterday and noticed he was looking for more room to apply force, he was working hard.
The extra leverage is the winner for me hands down. I have no scientific evidence just my experience.
 

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I am looking at a new bike but it has 170 mm crankarms....is there pros or cons to shorter crankarms? I am just under 5'10 average inseam
I just got through reading about this below.

Good luck,



The "logic" of "crank length should be proportional to leg measurements" has been around for a LONG time, and lots of people have turned that "logic" into a formula for determining crank length. Only one problem: the research doesn't support it. One key feature that is often ignored in these discussions is the duration of muscle contraction that is controlled by cadence. It just may be that there is an optimum here, which is why there is a fairly narrow range of cadence for optimum performance. Longer cranks tend to mean lower cadence, moving you out of that optimum range. Crank length has been a point of debate since the introduction of the "safety" bicycle in the late 1800s, and there have been all sorts of fads in that regard.

There is no reliable formula for predicting crank length. There ARE lots of formulas out there, but they are just figments of the imagination of their purveyors. No one has ever done a study that shows how crank length should relate to anything.

You will find no high quality data to support any particular crank length as being better than any other. This is true whether or not you correct for leg length, femur length, etc. On the other hand, you will find lots of anecdotal or low quality data to support all kinds of conclusions, and more theories than you can shake a stick at. A rider's response to changes in crank length is 1) highly individual, 2) dependent on riding style and the event (TT, climbing, crits, track racing, etc.), and 3) most important, highly adaptive. This is why it is so hard to study the effect of crank length.

A 2008 study by Jim Martin, Ph.D., from the University of Utah shows zero correlation between crank length and any performance factors.
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Fred Matheny Summary: There have been studies of crankarm length, but the results aren't consistent. Some show that longer cranks provide greater leverage for turning big gears. Some show that shorter cranks foster greater speed via a faster cadence. And some show that crank length is completely individual.

So, longer crankarms aren't a panacea for time trialing. In fact, there are dangers associated with them. The added length makes your knees bend more at the top of pedal strokes and extend more at the bottom -- both of which can lead to biomechanical injuries if you jump from 170 mm to, say, 180 mm.

Also, longer cranks reduce cadence -- and a brisk cadence is the key to good time trialing.
 

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I'm a little over 5'7". Not that the feel of crank length differences is profound, by any means, but I've settled on 172.5 as my favorite.

It might also be asked, if the crank length doesn't make a difference, why do (or more accurately did) the major component makers provide a choice?
 

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Let's make this simple. If you have no knee issues, go with 172.5.
If you have had knee issues in the past (but not currently), and you think you may develop knee issues down the road (because you will plan to ride a lot more), then go with 170.

When in doubt, go with a shorter one.

I'm 5'7" and using 170mm now, but I wish I had gone with 165. Reason is I'm becoming more and more of a spinner, so short is better. Also, I do have pedal strikes sometimes, so again shorter is better.
 

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If you have no knee issues, go with 172.5.
If you have had knee issues in the past (but not currently), and you think you may develop knee issues down the road (because you will plan to ride a lot more), then go with 170.

When in doubt, go with a shorter one..
Oddly, I have less knee pain with the slightly longer crank arm. The longer length allows my knees to more closely achieve their natural flexing arc. On the shorter crank, my knees start to complain because they're unable to get quite high and bent enough.
 
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