Functional leg length

I’ve been to five fitters and nobody seems to know how to deal with a functional leg length discrepancy. It’s causing me back pain comfort issues on the bike. Adding a shim would add length to my bone and therefore hike my hip on a upstroke.

How of this dealt with???

Cleat stagger?
Minimal shim?

I reduced my crank to 165.

Please help

3 years ago when I was going through physical therapy the PT noticed I had what appeared to be one leg shorter than the other.
He wanted to be certain of this so we went through all kinds of methods to insure an accurate measurement of my leg lengths. In the end he determined that I had functional leg length discrepancy. Further evaluation showed that the problem was from me pelvis being twisted and out of proper alignment. From there we added in therapy exercises to correct the problem with the pelvis and thus the leg length discrepancy went away.
Possibly you could consider this possibility instead of using shims which may not address the actual underlying issue.
It helped me a lot.


Firstly (as jbruced says above) you need to know if it is a structural LLD or a functional one - if it’s functional, shims will just make things worse but cleat position changes may help. Physio/strengthening/stretching/chiro etc is needed for this.

If it’s a structural LLD, you need to know if it’s coming from the pelvis/hip, femur, tibia or a combination. For example, if it’s all in the femur, your knee/shin/foot (on your short leg) will be closer to the back wheel with that pedal forwards (ie cleat needs to be closer to your toe), but at the bottom you’ll need a shim to equalise the length. If it’s all in the tibia, with your pedal forward your hip will be slightly less flexed than the longer side but the knee will be the same distance from the back wheel - you’ll still need a shim for the length but no cleat position change.

Go on youtube and find Neil Stanbury, he’s a bike fitter and (I think) physiotherapist from Aus, he really knows his stuff. There are a couple of videos about LLD, on the Road Cycling Academy channel IIRC.

Two important rules: 1. start with cleat position and work up. 2. remember your goals - are you after comfort or performance (it’s hard to perform well when you’re uncomfortable though)?


Thank you for your reply! For me it’s functional and I’ve been working with a therapist for several years. But for some reason we just can’t get it past a specific point of remedy. It’s a problem with my hip/pelvis being twisted. I’m glad you were able to remedy your issue!!!

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Ah thank you for such a detailed response! You know quite a bit about the topic!!! So far cleat staggering is what we are trying. It did remedy some unequal feeling of my legs to one another. But I think it’s causing some cns issues and it’s causing me some other problems. The stagger is quite significant. I’m twisting with my lower body to the left. Right leg is closer to the top tube. Causing saddle discomfort, back pain, biomechanic inefficiency on the bike.

I actually am considering this! I’m wondering how bizarre it would feel and also would need to speak to my fitter regarding if a 5mm short crank on that side would be beneficial. Also I’m assuming it’squite difficult to just get one crank arm. But also wouldn’t be looking for anything Costly. Just in case I had it temporarily (unlikely) or it just causes other issues.

Thanks for the suggestion!

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Look do (or did) a crank that has a triangular pedal insert that lets you change lengths. Not a cheap way to do it though!

That’s funny, now you mention it I’ve just realised that I’ve always felt that my left arm is longer on the bike - I’m always shifting my weight ever so slightly over and I can always see the right fork leg but not the left. I also get saddle numbness from time to time, but I never associated one with the other before. Maybe I need to take some of my own medicine and get a proper fit done…

Debated chiming in as you’ve received some good advice from some PTs in the thread. I figured I’d contribute though and note that if your issue is truly functional, then you need to 100% exhaust all options of figuring out the true cause of the twisted pelvis prior to doing any form of shimming or drastic change like using a different crank length on each side.

Is it possible you have some form of ankle issue on one side that doesn’t allow you to get as much heel drop as the other in the pedal stroke which filters it’s way up the chain to your pelvis? Is it possible you’ve got some issues with your shoulders or T spine that’s filtering it’s way down to the pelvis? Things like that are all things that should be exhausted before doing anything else if your legs are truly the same length and it’s a functional issue.

I’ve been on a bike (triathlon) for 22 years now (I’m now 40), and have had an imbalance since I started with my weight shifted to the right. I had minor annoyances for 5-10 years and then it got more pronounced. I saw PTs and spent thousands on bike fits. Eventually I shimmed the “short” left side and lo and behold it felt ok, but over the course of years it got worse and worse. About 6 months ago things got to a point where i couldnt sit, sleep, ride a bike, or run without massive pain on the left side from spine through to the hip. I had imaging done and my legs are the exact same (within tolerance), and there is nothing in my pelvis that is incorrectly shaped. Turns out the problem is I have a vertebrae in my t spine that’s significantly out of place and when on the bike I shift everything to the right to avoid problems holding onto the bars.

Put all of the above together with 200-300 miles on the bike per week for 22 years and I now have an SI joint on the left side that massively inflamed and will not calm down.

I hope that wasn’t too long, and it is only an n=1 story. But I do really wish I’d have thought twice before shimming.

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That’s good advice. Although I’m curious what the spec tolerance is on a leg length difference? :slight_smile:

For the record I’m an orthotist - I tend to say less than 5mm you can ignore, rarely have I given someone a raise of <5mm. But I have had people with an LLD that have a significant improvement (or regression) by changing their raise by only 1-2mm, or have at least felt it was better/worse.


Oh wow!!! I’m glad that you shared your story!!! I’m so sorry that you are dealing with so much pain!!! You have a very intricate issue and yes it seems your shin exaggerated the issue to where you are today.

It’s super hard to know where to go from here. I’m staggering cleats currently. I’m happy in some regards but others are a problem for sure.

It’s been 8 years that I am aware of with this issue so I don’t foresee it going away any time soon. I do mobility and strength and it remains.

I’ll probably have to settle for comfort where I’m at now if I can’t figure out where to go with it

Hope you get your issues under your control to a pain free place!!!

That’s curious for sure! I think I read somewhere that most of the population has some form of functional or structural LLD but many do not even realize it. It doesn’t bother them or cause injuries. For those it does, it’s seemingly a nightmare. I too maybe thought a tiny shim 1-2mm with a slight cleat stagger might be the best of both worlds without fully committing.

Might be worth talking to my fitter about a compromise idk

I have a leg length differential that has been measured by PT/sports med doc. My differential is 12-13mm. I always suspected something was wrong but didn’t know how to begin the search regarding what it was. I’m short on the right leg so all the compensation I did over the years generated significant ITB syndrome in the left leg. Over the years I also began to see a patella shift to the outside of the left leg that generated debilitating knee pain. That was traced to a muscle imbalance in the knee that was also traced back to the compensation I was doing to make up for that 12-13mm differential. Once diagnosed my fitter installed a 6mm shim on the right side to make up half the differential. Its my understanding they never try to make up more than half of the differential. Your body will take care of the rest. Both the ITB and patella shift issues disappeared immediately aided by some PT I did to bring things back in line. This was about 2 years ago. I was at the point of hanging the bikes up due to knee pain and ITB on the left side. No end in sight now and I just turned 80. There’s no way I’d be on the trainer under load if this issue had not been solved. I don’t do any road time any more given the attention span of some drivers these days. But I love the trainer for cardio pulmonary conditioning. I might suggest finding a bike fitter rated at 3 or 4 on the IBFI scale. (International Bike Fitting Institute) Long story short, anyone can call themselves a fitter, but there are differences to be found in those who meet the requirements of the IBFI. Not to suggest a non IBFI fitter can’t get the job done, but at the consumer level, we need somewhere to start in order to at least begin the process of differentiating between them. My guy has earned IBFI 3, almost to 4, teaches fitting internationally, etc. so he knows his stuff. Not cheap, but looking back there has been no better investment related to cycling. (Doesn’t matter how cool the bike is if it hurts too much to ride!) He also runs a 2 to 3 month appointment backlog during cycling season which I consider a great indicator for the product he’s turning out. Maybe also talk to local amateur racers or clubs and find out who they use. Nobody wants to hurt on the bike and most are anxious to share the identity of the fitter who got them out of trouble or keeps them out of trouble. Anyone who is racing or looking for results and spends a lot of time on the bike will usually have opinions about fitters.

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Never heard that idea before, an interesting take (I assume you heard this from the person who did you measuring/gave you the shim?). I tend to go about 80-85% of the difference, but my rule of thumb is to go with what the patient feels is right (although most people I see are just regular folk walking around, not trained athletes riding bikes). But I certainly would never* give anyone a raise that was more than their LLD, so as not to upset the apple cart.

*maybe to younger kids to stimulate bone growth, and very rarely to adults but usually only after a fracture/surgery and only if they felt they needed more.

Another tip I got from Neil Stanbury is, look for fitters who offer free adjustments and a money-back guarantee. If they’re not prepared to stand by their skills and admit when they can’t get it right, how much can you really trust them? Same goes for mechanics to some extent.

…interesting. I’ve recently been toying with the idea of loading another mm or two into the right leg shim. Spending all my time on the trainer I have become very perceptive/sensitive to saddle height and pitch, much more than I ever was on the road. I’ve learned what the distinct hamstring signals are for saddle too high or saddle too low. This is not something that happens right away, but over 15 20 minutes under loadI can feel the fatigue begin to build. A very small saddle adjustment can eliminate it. I have also seen the I’ll have the “saddle too high” feeling in the right hamstring with no such feeling on the left which leads me to suspect the right leg is still reaching just a tad and may appreciate a tiny boost in the shim. (Never done experimenting!! just gotta remember where I started so I can go back to the beginning setting if the experiment doesn’t work.)

BTW, I did learn of that 50% rule from my fitter. He’s very careful about “too much of a good thing” on all fit adjustments. His preference is to try it out and come back in for fine tuning if that seems indicated. I’ve learned I can sense a lot more after many miles on the road or hours on the trainer than I can from a short burst on the fit stand. If there is any question, its much easier to “sneak up” on a setting rather than taking too big a bite in the first setting.

Yes, the 50% is at least covered in the original Specialized Body Geometry fit philosophy, that was formed by Dr. Andy Pruitt as part of his long history in fitting. I think other methodologies apply similar limits to adjustments like this.

At least part of that is the consideration that a person with a discrepancy like this is dealing with it in their daily lives, not just cycling. Some may be making adjustments in their shoes for walking, running and such, but not everyone does. So, “fixing” an apparent problem to a “perfect” resolution may lead to other, unintended consequences.

And at times, there are good reasons to skip an adjustment all together, in the “do no harm” mentality. Changing something that just seems different without a direct need to do so can create more problems than it actually solves. These tricky bits and the fact that we are also dealing with the complex interaction between two humans is what leads to the mixed results that some have with fitting in general.


You have quite the story!!! It’s amazing how everything is connected and it’sa chain reaction in the body when something is adjusted.

How long did it take you to notice a positive difference with your shim??

I’m doing a ton of off bike conditioning and any strength work I do unilaterally. That’s made a huge difference in my strength and balance of muscles.

Nobody has been talking about the upstroke of the pedal. Surely if you have a functional leg length issue, the bone isn’t the problem. So do you not find that the knee and hip hike up more so on pedal stroke when the knee comes up?

Everybody has different means of fitting. I’ve experienced many of them. It’s nice that others are able to verbalize their experiences. This thread has been great.

You have an interesting take also! How are you able to measure that 85% value with a functional discrepancy??

Do you find you have a good response to your methodology??? As above I stated that I was curious regarding feedback on the upstroke of the pedal. Concerned about the hip hiking up and knee coming up as a result of the shim. With a functional discrepancy, I would suspect it to be problematic potentially.

I was fit at one time with a 1cm shim. It felt good initially until my cns was like what the heck on the upstroke. It was causing me almost to rock the opposite way. Could have been too much and was definitely likely it was. Curious your take on that

So this is interesting. Your experience resonated with me. My fitter tried a cleat stagger with me initially which made me feel the most balanced I’ve felt on the bike ever.

Before that I could feel 1mm of change in any aspect of my bike and would not handle it well. Oncewe tried a cleat stagger I’m far less sensitive to changes. I’d say it improved 70%. I just assume because of the balance and the leg was reaching less.

I’m not sure if that’sa message from the cns that something is really unbalanced??? But I find I can actually have a range even if it’s small of adjustments and I’m not crazy sensitive like before