Originally Posted by
Bacciagalupe
FWIW, I doubt that the tolerances on leg and foot position are so high that you would genuinely notice a 2.5mm difference in crank length.
Nor do I believe that humans are really that sensitive. I'm fairly confident I could alter almost any single parameter of your bike's setup by 2.5mm without you noticing.
If you altered my seat post height by 2.5 mm I would notice it by the pain in my left knee after 20 miles or so. I would imagine longer/shorter cranks would have the same affect as raising/lowering your seat in term of leg extension. My left knee is
very particular for some annoying reason. Probably cause a horse kicked it when I was 6. I literally lowered my seat by 2mm and the pain was gone forever.
As for the "advantages" of crank length I definitely agree with you. I don't think there are any. As pwdeegan said, gears can be used to control cadence and mechanical advantage. I'm not
quite an engineer yet though
Give me a few years