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Leg length discrepancies
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Any others using shims to help fix up leg length problems? Just fit 2mm to my left cleat.

Before fitting, I would regularly see 50/50 left,right power from my powertaps. Sometimes it would report left being a little stronger.

Since adding the shims, I am often seeing 47-49 on the left. Surprised it could affect that much but would like to try and fix

Ive always had my saddle height set so my left leg locks out when heel is on the pedal. Now that Ive fit the shims, I presume I should probably add 2mm or use my slightly longer right leg to set the saddle height?
Last edited by: chatlow: Feb 20, 21 6:40
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Re: Leg length discrepancies [chatlow] [ In reply to ]
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DISCLAIMER; not a bike fitter just a bike fitters worst nightmare haha


I have 8mm of shims I believe for I am extremely wonky in proportion after disagreeing with a van, However in the fit when they were fitted I was at 48/52 ish and went to almost dead on 50/50. I had been compensating (and still do as that's circa 1/2 the difference in leg length) which probably explains the power difference (or lack thereof for me) as I'd got used to adapting how I ride for it. My saddle did go up from doing this, but to a middle ground where both legs were happy rather than based off either individual one. In general any change will cause more difference than you think until you are used to it, I wouldn't be surprised if it does go back towards 50/50 as you teach your body it doesn't need to compensate so much anymore.

As an interesting anecdote my running I have a 3mm insole on top of the normal insole in my shoes (no point me having a heel wedge as a midfoot/forefoot striker) and still have near identical ground contact time for each foot according to garmin, and this only changes when my form has absolutely fallen apart (we're talking the kind of fallen apart that makes people dial two digits of the emergency number incase they need to call me an ambulance style fallen apart here)
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Re: Leg length discrepancies [chatlow] [ In reply to ]
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Were you having any injury issues with your previous setup? Not that a perfect L/R balance is the end all be all, but with the info you've provided to us it kind of seems like you found a solution for a non-existent problem.

Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
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Re: Leg length discrepancies [chatlow] [ In reply to ]
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My wife and cycling partner has a 2cm leg length discrepancy (smashed femur from a decades old car accident, measured by x-ray), so she has a 1-1.5cm custom shim under her cleat (I just dremmeled some MDF, can't remember the exact eventual height, but a bit more than half the discrepancy). We've never checked her L/R power differences, but it wouldn't be meaningful since she also had a large right hemisphere parietal stroke from the same car accident and has significant left side partial paralysis including the left leg.
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Re: Leg length discrepancies [BudhaSlug] [ In reply to ]
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BudhaSlug wrote:
My wife and cycling partner has a 2cm leg length discrepancy (smashed femur from a decades old car accident, measured by x-ray)


That's about the difference I have in one femur, though it seems I was born with it. For a femur discrepancy it's best to use a shorter crank with the short leg, and less of a shim. Else the knee on the short leg will need to lift higher, which I don't think you want, especially if there is a mobility issue. The short leg will also be reaching more in the power phase if the cranks are the same. You may want to get rid of the shim altogether (which is what I did). I also have the cleat moved a bit farther forward on the short leg.
Last edited by: rruff: Feb 20, 21 9:15
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Re: Leg length discrepancies [rruff] [ In reply to ]
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Thats a great idea that I hadn't considered. It would be semi-straightforward on our tandem since our current cranks are basically individually made and square taper. I'll have to email them and see what it would cost to make a new NDS tandem crank (which is where the crossover chainring mounts). On any other single bike its also not too big a deal (although it can get expensive if the cranks don't come individually).

Can I ask about how you decided on how much crank length difference to go for?
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Re: Leg length discrepancies [BudhaSlug] [ In reply to ]
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I went 50 years with no compensation and still don't compensate for walking and running. I just did 5mm at first, and made a 5mm spacer, and had the cleat on the short leg 5mm farther forward. That corrected for ~half the difference at the bottom and forward part of the stroke, and the femur angle was about the same at the top. My short leg and hip are kinda gimpy though, so I eventually got rid of the spacer which made it easier to come over the top. I liked it better, and that's where I still am... on the road bike. When I got new cranks for the TT bike a couple years ago I found a good deal on individual NOS Dura Ace square taper (great for low Q setups), and have 172.5mm for the long leg and 165mm for the short one. My short leg still has a tougher time making the circle than my long one. I think 1cm difference would be even better and possibly with a small spacer then.
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Re: Leg length discrepancies [rruff] [ In reply to ]
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I have a full 1 inch difference. Got hit by a drunk driver as a policeman directing traffic. I raced for about 10 years with a 1/4" wedge under the right cleat. I never used anything for running. After those 10 years and for the last 20 years I've not used anything to makeup the difference. I've compensated on the bike by peddling more toe down on the short right leg.
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Re: Leg length discrepancies [chatlow] [ In reply to ]
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chatlow wrote:
Any others using shims to help fix up leg length problems? Just fit 2mm to my left cleat.

Before fitting, I would regularly see 50/50 left,right power from my powertaps. Sometimes it would report left being a little stronger.

Since adding the shims, I am often seeing 47-49 on the left. Surprised it could affect that much but would like to try and fix

Ive always had my saddle height set so my left leg locks out when heel is on the pedal. Now that Ive fit the shims, I presume I should probably add 2mm or use my slightly longer right leg to set the saddle height?
When I was fitting, I was always pretty adamant about not adding shims. I felt like it was beyond my scope of practice.

Additionally, not all discrepancies are structural and even if they are, a bike fitter's goal isn't symmetry. You don't sit perfectly centered on the saddle, you don't live symmetrically, you are not neuromuscularly wired symmetrically (you have a kicking leg, a leg you prefer to jump off of, etc.), and odds are (except in some of the extreme circumstances described in this thread) the body has adapted to whatever asymmetry you're dealing with. So shimming probably isn't fixing anything, it's either creating a new problem or just moving the existing problem.

I did have a couple of athletes who did have shims when they came in (similar stories to those on the thread - significant car accidents), and I just fit them normally and left the shims as they were.

Trent Nix
Owned and operated Tri Shop
F.I.S.T. Advanced Certified Fitter | Retul Master Certified Fitter (back when those were things)
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Re: Leg length discrepancies [trentnix] [ In reply to ]
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I have a 10mm discrepancy. No injury or trauma , just came that way. I have never used anything for running or cycling or any other sport for that matter. Given time I think bodies adapt to these idiosyncrasies.
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