Originally Posted by
Kapusta
While differing crank lengths do get around some issues that a lifted shoe or cleat would create for the OP, they do start to introduce a different issue: differences in leverage.
When I was playing around with different crank lengths deal with my discrepancy, what found was that once I got to 10mm difference, it felt like I was in two slightly different gears. 20mm would be really noticeable.
Leverage difference didn't occur to me, we had my wife's cousin do this, he has a 25mm difference and he never mentioned anything on it. The difference was causing knee pain from lack of full extension, might be he just expected the shorter leg to have a harder time pushing and didn't give it any thought. Is a good thing to be aware of though.