It's very simple to figure that out. Simply use the heel-on-pedal test with each leg. That'll tell you. I have one leg that's much shorter than the other, so I shimmed the cleat on the short leg, though that's still not enough. The problem with shimming cleats a lot is that then your knee comes up higher, too, so that's still not optimal. Optimal would be a shorter crankarm on the short leg side. I'm not motivated enough by any problem to bother with that.