I actually have the EXACT same discrepancy in leg length...and its on the right side as well.

For running I have learned how to compensate with my movements. You can really fix the issues with proper form. I don't shim at all with my running.

For CYCLING I shim my right cleat (bike shoe). It has made a world of difference and I have had two bike fitters comment on how much of a difference the shimming will make. I no longer get knee pain on the bike when holding proper form.


Shim the bike shoe and try fixing the run pain with proper form.

A functional discrepancy that isn't anatomic may come from rotated pelvic / spine structure. I'm not an expert in this area, but 20mm seems like a lot for a functional different. These have the potential to be "reset" toward no leg length difference.

Anatomic differences would come from the Tibia (Lower leg bone) or the Femur (thigh bone).

• Femoral differences (because the femur is mostly horizontal while pedaling) are typically dealt with through a cleat shift forward on the shorter side or rearward on the longer side.
• Tibial differences (because the tibia is mostly vertical while pedaling) are typically dealt with through a lift under the cleat

In either case an offset of half the leg length difference is a good place to start. In your case this is ~10mm.
However, without more information it's hard to know which you should do.

Try this:

1. Lie on your back, have a helper at your feet, gentle grasp and apply traction to your ankle. Slight swaying back and forth from the helper can help to align at the hips.
2. Once settled, bend your knees and hips to place your feet flat on the floor so that your legs back a triangle.
3. Have your helper align your feet perfectly together.
4. Then have them check the position of your knees.
5. Think about this like the legs of a triangle.
6. If the Tibia is shorter, the knee will be lower and closer to the ankle
7. If the femur is shorter the knee will be lower and closer to the hip.

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My discrepancy is all in the femur ~20mm. I've been using a 5mm shorter crank on the short leg, 5mm spacer, and cleat 5mm farther forward. It seems like the best compromise.

Mine is in the tibia and I only go with the cleat spacer.

I like your solution though...interesting.

I have a similar imbalance. It matters where the imbalance is (upper leg, lower leg) but Specialized makes great shims (I used to make my own by dremeling LOOK cleats if you are a DIYer. I also added specialized arch supports and both of those things helped. Oddly, shorter cranks made for pain which I had never had. I also don't have a problem running (unless I am overweight and I get a back issue slightly) and found that half of the discrepancy is the sweet spot so I would start with 10mm.

I also started doing 1 leg step ups at 10-12 inches starting at 1 min each leg working up to 10 minutes each leg with no rest and I think that helped me be more aware of what was out of balance. I have a friend who has the same thing and we tend to get injured way less then our peers and we think it is due to an issue presenting itself early so you cant grind it into a bad deal.

For run, I take my left sole out now. Wish I knew to do this 4 years ago, as I struggled through various injuries. Perhaps I should try to some how lengthen my right leg

That makes sense. The tibia is fairly vertical when pedaling particularly in the power phase. Femur differences are more complicated.

So, because the shorter crank arm contributes differently as it moves through the arc:
At "3 O'clock" you're effective working with 10mm of shift and 5mm of lift. (When the femur is more horizontal)
At BDC you're working with 5mm of shift and 10mm of lift (When the femur is near it's most vertical)

That's a great (albeit difficult for some to obtain) solution! Especially because the changes in femoral angle are approximated by changes in crank arm orientation.

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I talk a lot - Give it a listen: http://www.fasttalklabs.com/category/fast-talk
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The above poster has eschewed traditional employment and is currently undertaking the ill-conceived task of launching his own hardgoods company. Statements are not made on behalf of nor reflective of anything in any manner... unless they're good, then they count.
http://www.AGNCYINNOVATION.com

I'm in this camp, and glad another poster included the bit about which way to address cleats depending on where the discrepancy lies.

I'm only 8 mm, but had so much discomfort built up that I was keen to shim all things. I didn't know about the right way to address my bike cleats, so spent 3 or so years experimenting with 4-8 mm of spacers. I settled around 4 before having a retul fit recently and being told what's been posted. Knowing which bone measured what, result was removal of shims from my tri shoes; I don't like it. I took the advice though and shimmed my road shoes down to only 1 mm. It might be I just need to get used to the difference, versus 1 mm really being better than 0 mm to address my 1 mm lower leg difference.

Running: I've shimmed 4-6 mm here. The issues are 1) comfort of the shoe is impacted by adding the shim (inside the shoe), and I can't just remove the insole for the long side b/c I seem to require good arch support or my feet cramp terribly; and 2) my shims are layers of 1 mm flexible plastic. It came as a block of 8 layers and I've pealed them down and cut them to size, but the extra force they experience while I run has led to the shim layers a) peeling apart from one another and b) scooting out of my shoe. One day I was running and felt this annoying rub at my ankle; when I finally stopped to take a look, the shim had worked it's way almost half way out of my shoe.

I've also tried a custom built orthotic (great arch support!) that has the heal of the short side built up (4 mm), but I don't like running in them. Fine for walking (landing heal first), but seems pointless for running (desiring to land mid-foot but it feels like my toes are slapping the ground). Initially, all the shimming for running felt much better. However I have to confess my run gait may be off. I seem to have issues recruiting muscles correctly so the answers to what hurts and why are still not clear for me.

Good luck. I find the process of experimenting on myself and with my setup tiresome. I hope it goes more smoothly for you.

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