Leg Length and Left/Right Unequal Power Meter Balance
 

All,
I've had a professional fit at Specialized in Boulder, so I'm pretty dialed in. After the fit I got a Dura Ace two-side power meter. Same crank lengths, all that. Saddle is fine, no hip rocking.

As part of the fit I've got my left cleat shimmed 2 degrees to help with outside toe pain.

Interesting on the power meter; over a 20 to 25 mile ride, my left/right power distribution is normally 55% - 45% or more favoring the left side. Never in a million years would I have guessed that I had lop-sided power that much to the left based on feel alone. This is not a new, one-off experience as I've had the power meter long enough to see a consistency in these numbers.

Now my question. Could my legs be of different length and/or could the 2 degree shim on my left cleat be causing this? I'm thinking about adding a cleat riser to my right cleat. Do you think this might help? When I consciously pedal to even power, my left foot hurts even less than when I added the shims.

Any thoughts to get to even power balance, other than pedaling to even power based on the meter? I'd prefer to not watch it all the time.

Thanks.

Glenn

Take out the shim and see what happens.

My prediction is that you will restore balance.

For years I've dealt with the outside left toe issue. The shims have really helped in that regard, but not totally. I'm reluctant to try that as a first line solution. But maybe that would help the balance, but then how to re-fix the toe numbness issue?

Thanks.

Glenn

Surprised your fitter didn't notice a leg length discrepancy. When I had a Retul fit mine did, and he gave me a cleat shim for the shorter leg.

I'm not sure that there is a leg length discrepancy. As you know, those Retul fits are pretty comprehensive. He didn't say anything about one. Did he give you like a 2 degree shim or an a flat cleat spacer? That's why I'm wondering if a flat spacer on my right cleat might make up for the shim on my left cleat.

Thanks
Glenn

Do you have another set of cleats without a shim? Or is the shim in the insole? I am not suggesting removing it permanently. But the scientist in me thinks you need an experimental control: power asymmetry in the absence of the shim.

(In my own case, I do have a leg length discrepancy. I tried a cleat shim and it was like torture. Now I just have one cleat set slightly further back.)

I have a imbalance as well perfectly normal and not something you can do a lot about or necessary need to.

Maybe I am mis-understanding. I am using shim as a noun, for some object you put between your cleat and your shoe, or possibly between your shoe and your insole.

If you are using this (as a verb) to mean the cleat is rotated 2°, disregard everything I said.

The shim is a separate part and is between the cleat and the bottom of the shoe, so easy to remove. Might should do a control. I do have custom insolse from Retul, however. Interesting on the "torture" and "further back."

Glenn

I was fitted with a cleat shim (aka stacker) for the shorter leg along with both internal and cleat wedges.

You're probably right, but the imbalance was something that got me to thinking "why" it was there and if there was anything I could do to fix it. As I mentioned above, when I watch the meter and try to get 50/50 it seems to help the pain in my outer left toes (numbness) more that just the shims in the left cleat do. Weird stuff.

Thanks.

Glenn

As Edward Abbey would say, I have a tendency to over-exaggerate. But I did have to stop mid-ride and remove it.

That's good to know. That's what got me thinking along the lines of my question. Thank you.

Seems like if the shim solves our pain, you'll be able to put out more power longer. With pain you'll be inclined not to put out as much power for so long.

I wouldn't care what the left / right balance is.

I've never measured my r/l power balance, but from what I have heard, it often diminishes at higher power output. Do you see any chages like that when you drope the hamer?

I was diagnosed by a (cycling) PT (unrelated Achilles issues) with one leg 1/2" shorter. First 5 minutes as soon as she saw me walk. I now wear 1/2" lifts on every right heel and 1/4" plate shims between ever right cleat and the sole. Life changing. (Plate aluminum bent to fit the sole curvature. Not easy or fun to bend! Bench vise. sledgehammer and a very long lever.) Edit: raised the seat the 1/8" difference between the cleats.

For the first time ever, I sight down the center of the front wheel and bike frame. Fewer seat issues and sores. Ride no hands in no wind with the bike straight up and down and in line with it.

I will pay attention to that.

That's similar to my line of thinking. My first inclination is to put a flat cleat spacer between my right cleat and the sole and see what happens. I'm gonna use the factory made ones, which only go to 3mm or ~1/8 of an inch. Thank you.

Here's another sick thought: could the difference be an artifact of the precision/accuracy of the two power meters? Is there any way to switch them? Can you get someone else to ride your bike and see if they have a similar imbalance?

After the changes, shim and seat height, I told the PT. She said that's exactly what she would have told me to do.

I've heard anecdotally over time that some meters may not be dead on. But these are consistent anyway.

They are built into a Dura Ace crank set so I don't think there is a way to switch them out. I calibrate them nearly every time my Garmin 1040 asks.

I ride entirely alone and plus I ride a 62cm, both probably hindering factors for a test rider.

I can get them to 50/50 by paying attention and it doesn't feel unnatural pedaling that way. But when I just pedal there is that imbalance. Again, my left toes feel better at 50/50 because, I guess, it takes some load off my natural pedal stroke favoring that side. That brings me back full circle to thinking my right leg may be a little shorter. Having my left cleat shimmed at 4 degrees (not 4mm in flat rise) seems like it would compound a shorter right leg length. That led me to the thought of putting a flat spacer on my right cleat.

Heck, I don't know what I'm talking about. I guess everyone's right and I just need to experiment and see what happens.

Thanks.

Glenn

Alrighty then, that's encouraging news. That's what I'll do. It's supposed to rain here for the next several days. I'll put some miles on and be back.

Thank you.
Glenn

I have heard that the 50% "rule" (shim 50% of leg difference) is good for those with legs that are of similar proportions, ie one leg is a scaled version of the other, but doesn't work so well (or at all) if the discrepancy is largely in the thigh (or calf). I seem to be a scale factor guy so I haven't tried to stretch my brain to figure out what would work for the thigh and calf people.

The easy solution is to not display L/R balance on your bike computer.

Why is the idea of using a shorter crank arm for the shorter leg frowned upon (vs a shim)?

The problem I had when I tried a shim was that the stack height really made it hard to tolerate, whereas the shorter leg only bothers me if the saddle is at the high/optimum for the longer leg. (This difference is small enough that I didn't notice it existed until my bike fitter/framebuilder mentioned it to me, but I can feel one leg can be over-extended when the other is comfortable.)

All,

Since we last talked, here's what I've done. I used one of these cleat risers on my right foot.

https://www.amazon.com/dp/B00BP52Y4Y...roduct_details

I went on four rides totaling over 75 miles.

1) August 22, 2022
17 miles, rolling hills and flats
Left/Right Power Balance = 54/46

2) August 24, 2022
17 miles, rolling hills and flats
L/R = 54/46

3) August 27, 2022
21 miles, a few more rolling hills and flats
L/R = 55/45

4) August 31, 2022
On this ride, I removed the cleat riser from my right foot
21 miles, a few more rolling hills and flats
L/R = 55/45

I've come to 2 conclusions

1) Focusing on L//R power balance doesn't matter for an amateur.
2) The Shimano dual-sided Dura Ace crank power meters are inherently inaccurate on L/R balance and total power output (lower) when compared to other meters. They are consistent within themselves, however. Shimano knows this but won't admit it. Interestingly, the drive side strain sensor is located closer to the bottom bracket than is the non-drive side strain sensor. You would think the L/R imbalance could be compensated for through firmware.

I base conclusion 1 one some of the posts above and conclusion 2 based on some research I've done such as

From DC RainMaker and Bike Radar
https://www.dcrainmaker.com/2018/04/...th-review.html
https://www.bikeradar.com/reviews/tr...-meter-review/
https://www.dcrainmaker.com/2022/05/...g-metrics.html

From Shane Miller GPLama

Hopefully this has been of some help to others. Thank you all for your input.

Glenn Atkins

the answer to this seems glaringly simple to me. drive side is on the right. your right leg will obviously have an easier time putting down power as a result. your left leg will have to compensate for this by putting out more power to match. mystery solved.

My left/right balance is in the range of 55/45, thus I need to put out more power in my right leg, not the left, to make it ~ 50/50.

Did you read my post #26 right above yours? A glaringly simple mystery already solved.

Regards

Glenn, how would I find out if one leg is longer than the other? Is there a test for that? My L/R is something like 45-48 on the left and as high as 55 on the right.

I had a bike fit at Retul in Boulder a couple of years ago and they didn't mention that I had a discrepancy. I forget exactly how they measured it.

I got it in my head that I may have a leg length difference when I consistently noticed my left/right power imbalance. It took a concentrated pedaling effort, which felt unnatural, to even out the power balance. I put a cleat riser (not an angled shim) under my right cleat and had no change so I took it out.

I did some research and considered the posts above and came to the realization that the L/R balance doesn't matter for an amateur and that Shimano is aware, and has been for a while, about the balance issue in their crank-based, two-sided meters.

A confounding factor for me was that I have always had left, outside toe numbness and hot-foot. But never in my right toes/foot - only the left. I also have peripheral neuropathy in both lower legs, not diabetes related. I thus began a journey to see if I could fix the numbness and hot foot.

1) had the bike fit, including custom Specialized insoles (done in 2020)
2) shimmed my left cleat (done in 2020)
a) i use one glove size above my normal. for example i use extra large instead of large
b) i use one shoe size above my normal size
3) more recently shimmed my right cleat (2022)
4) tried and then removed my right cleat riser (again, not a angled shim) (2022)
5) moved both cleats to the rear as far as I could (2022)
6) just within the last week went from a 138mm saddle to a 155mm to a 165mm saddle (2022)
7) just within the last week moved my seat forward 15mm, yes I know that's a lot even though it's only about 6/10 of an inch, but I'm relatively older and don't yet have enough flexibility (2022). I've been off the bike for a year - some from laziness but almost six months due to a severe right calf injury unrelated to cycling

I may raise my saddle some to compensate for its move forward, just don't yet know how much to move it.

What clearly helped the most with outer toe numbness and hot foot in my left foot was moving the cleats completely to the rear. Second best was shimming the left cleat and the bike fit. That's where the left shim came from. The fit mostly took weight off my hands.

I did 18 miles last night with all the above in place. Problems largely resolved even though it's a sample size of one.

Next on the list of things to try if the above don't continue to work include:

https://mid-foot-cycling.com/
https://www.g8performance.com/insole...ievers-bundle/

I do not have any affiliation to any product mentioned in this post.

Glenn