"If you had a shorter crank on one side, it would make up the leg length difference at the bottom of the stroke only. At the top of the stroke, it would have the opposite effect. The crank on the shorter side doesn’t come up as high as the other side which means the shorter leg is having to extend further not only because of the leg being shorter, but also because now the crank doesn’t come up as high. "
Uhhhmmmm… No.
This makes absolutely no sense. You’re mixing up extension and compression, and are totally mistaken as to how the leg actually functions during the pedal cycle.
Mixing crank lengths can be useful in compensating for leg length differences, specifically femoral diff. Shims are better suited for addressing a lower leg length difference. If you look at the leg as a series of connected levers, and view it’s motion during the pedal cycle, this is actually fairly easy to see. A short cut is to imagine the crank arm at rest dead parallel to the ground. If you add shims, how does this effect the leg? Now shorten the crank arm - what is the effect? If you can visualize the difference, you can see how the 2 different methods of compensation work.
If a persons upper and lower leg are shorter, the best method, if the difference is substantial, is to use a combination of shims and crank length manipulation. It may also be useful to play with saddle twist, as orientation of the pelvis/hips can be a useful tool to address this problem as well.
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