# crankarm lengths for different leg lengths



## mtnspectre (Aug 16, 2012)

Wondering if anyone else has had or come across this issue...My wife has significantly different length legs which cause her to sit to one side of her saddle. I was wondering if it were possible to use a longer crankarm on the short leg or shorter crankarm on the long leg and maintain a good spin?


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## kbiker3111 (Nov 7, 2006)

What is of different length? Feet, tibia or femur? Or is it soft tissue related? Usually spacers are a better solution than different length cranks. I have a friend with a surgically repaired tibia and a 30mm spacer completely solves the problem for him. The only situation where different length cranks makes sense would be femurs of significantly lengths.


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## wim (Feb 28, 2005)

kbiker3111 said:


> Usually spacers are a better solution than different length cranks..


Agree. The problem with using a different length crank arm is that depending on the arrangement, either at top dead center or at bottom dead center of the crank circle you are making the limb length discrepancy worse.


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## Stephan (Jun 24, 2011)

I will give what I did in my situation. My right leg is 1cm+ shorter then my left. I had been in contact with the paralympic cycling coach of Canada through my own coach and he suggested different crank lengths. I use a 165mm crank on the right side and a 175mm crank on the left. I went to a fitter who thought I should have had the longer crank on the right, but not so. After he saw me ride he realized that I had the right set up.

I have just begun using clipless pedals with shoes and the most important part is to get the cleat placement right. In my situation my left cleat is more forward then my right. This allows me to sit centered on the saddle and I am not rocking anymore.

I have said it before on this forum, I am not an expert, but situations like this take a lot of trail and error. Don't become discouraged, be willing to do some research and you will eventually find what will work for your wife. I know in Canada there isn't much information about adapting a bicycle for different situations, it took me almost a year to get my bike to where I feel comfortable with it. Try getting in contact with your paralympic association, maybe they will have some hints or ideas that will take some of the guess work out of the process.

Stephan


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## looigi (Nov 24, 2010)

A common way of accommodating different leg lengths is to shim the cleat on the shorter leg and/or move it forward on the shoe. The usual is to add a shim half the difference, so use a ~5mm shim for 1 cm difference. You can try that and then also try moving the cleat forward 5mm or so.

One other tweak that my be beneficial is to rotate the nose of the saddle a few degrees toward the long leg.


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## QuattroCreep (Nov 30, 2009)

Some leg length problems are caused by a tilt in the pelvis to one side or the other. The tilt can happen for a number of reasons, muscle imbalance, flexibility issues, past injuries, weak core strength, less then ideal bike fit. 

I would start by identifying what is causing the difference. If it is a pelvic tilt there are ways to fix it without shims, but it will take work off the bike, stretching and working out.

If it is a difference in the bone length I would look at shims before different length crank arms. Also if a large amount of shimming is need 8mm+ consider switching her to speed play pedals if she is not already using them. Speedplay have a lower stack height (8.7mm or 11mm) then other road pedals. (Look keo 17.5, keo2 15.7). This allows you to shim her short leg more without raising her foot too high above the pedal axle that it starts causing other problems.

Good luck,
Shaun


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## wim (Feb 28, 2005)

QuattroCreep said:


> ...I would look at shims before different length crank arms.


Just to clarify my previous post: I don't think different length crank arms are the answer to leg length discreprancy issues, be they actual or functional.


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## Whale_520 (Aug 16, 2012)

mtnspectre, 

I'd highly suggest seeing a fit specialist about this. As everyone here has pointed out, there are a lot of different types of leg discrepancies, functional (such as muscle imbalance or arch collapsing) or structural (bones shorter etc). There's also a lot of different fixes and usually a proper fit requires more than one if the discrepancy is large. I haven't seen to many cases where different length cranks are used but shims and cleat fore aft position (especially if it's femur length discrepancy) are common.


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## rayms (Sep 11, 2013)

wim said:


> Agree. The problem with using a different length crank arm is that depending on the arrangement, either at top dead center or at bottom dead center of the crank circle you are making the limb length discrepancy worse.


I do not follow this Can anyone explain?


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## JCavilia (Sep 12, 2005)

rayms said:


> I do not follow this Can anyone explain?


if you put a short crank on the side with the short leg, the pedal will be higher when the crank is down (good for the short leg) but it will be lower when the crank is up (not so good -- leg angle will be different). A spacer or shim between shoe and pedal will raise it the same amount whether up or down.


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## Lombard (May 8, 2014)

wim said:


> Agree. The problem with using a different length crank arm is that depending on the arrangement, either at top dead center or at bottom dead center of the crank circle you are making the limb length discrepancy worse.



^^^This^^^

Your best bet is a spacer between your shoe and pedal.


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