I've heard that for various reasons, many people's left and right legs do not extend equally when sitting on a bike seat. One bit of guidance I've seen for setting saddle height using a heel-on-pedal method, is to settle into the saddle, unclip and without rocking pelvis to either side, set the saddle height for the "shorter" (whether actually shorter, or just not extending as far) leg. So as not to be over-extending that leg. One consequence I guess would be that on the "longer" leg, it's not able to extend as far as it would like, and perhaps if that longer side is close to hip impingement, lowering the saddle and forcing the hip to come up higher would not be good.

An alternative which I've seen is that the "shorter" leg should get cleat shims, so that both legs could more or less be extending evenly and in their happy range, without having the saddle too low so as to contribute to hip impingement. I've read where some people say that shims can cause other issues, but haven't read any specifics on what those issues are.

I have seen reputable bike fitters advocate for each of those alternatives. So I'm curious what folks have experienced -- have you tried shims vs setting saddle height to the shortest (aka least-extending) leg, and which has worked out best? I've often heard that slightly too low saddle height is less likely to cause problems from a slightly too high saddle height, yet still some fitters seem to prefer shims over lowering the saddle.

I have a slightly shorter right leg. Rather than cleat shims -- which can cause problems -- I use a green Spenco "insole" under the regular insole. (It's flat, without any arch, and only 3-4 mm thick, so you can't really call it an "insole.") I can definitely generate more speed/power with that setup, as opposed to lowering the saddle for the short leg, and I feel more balanced when pedaling. (Try doing single-legged pedaling on a trainer, you'll see what I mean.) But you'll need shoes that aren't too tight to do that.

I've seen one bike fitter state that a lot of leg length discrepancies that he sees are just people that got into a habit of holding their pelvis a certain way. Particularly when they get on the saddle. And that with physical therapy or just awareness of how they sit, it can be improved.

Even riders without leg length discrepancies use different shims on different feet. So if it works for you then great. I'm not seeing that you are complaining of any pain. So are you just hunting a cure for nothing?

I went to PT for other issues 10 years ago. First thing she had me do was walk the length of the room away from her, turn around and walk back. "Your right leg is shorter." She sent me home with 1/2" heel lifts and told me to use them for all my shoes (or have a cobbler add 1/2" to the sole thickness). I figured going half that thickness between cleat and sole ought to work well on the bike plus up half that thickness for the seat. Made 1/4" shims. Seat up 1/8". Told the PT. She said that was exactly what she would have told me.

On the bike - everything just felt right. And for the first time ever, I could look down and sight along the lined up bike tubes/front wheel. 10 years later, I just take those shims for granted. (The shims, 1/4" aluminum plate drilled through for the cleat bolts and bent to the shape of the sole. Bending 1/4" plate isn't easy! An old bench vise, 5 pound sledge, a large crescent wrench and pipe extension.} Now the MTB style shoes also needed sole extensions and I've glued on sole rubber with 3M 5200. (5200 is good stuff. Expensive, hard to clean up, the tube will cure days after opening so line up a bunch of projects. We used it to glue and seal sailboat decks to the hull. Yes, bolted down every 6 or 8 inches also, but you could remove all the bolts and pick that 34 foot sailboat by the deck (if the fiberglass didn't de-laminate; the 5200 bond wasn't going anywhere).

I could have ridden the rest of my life with unequal legs with no pain or complaints (other than the usual getting old and the consequences of many thousands of mile). But correcting it has been a revelation.

Well what was the revelation? Did you suddenly increase speed or were able to put out more power for longer periods of time?