Originally Posted by speedemon
Yea, I did a search and didn't come up with anything defining the actual formula to get the size I needed. I’m 5'9" my crotch to the ground is 31.5" or 80cm. The gear I'm going with is a triple 30-42-52, 12-25. Is there some sort of a formula to find the correct arm? I'm trying to do as much research as possible before finalizing this order to make sure I get everything correct.
Let me ask you a quick question. Do you feel like you have short legs for your height? The reason I ask is because 31.5 inches sounds more to me like a pants inseam length than a bicycling inseam length for somebody who is 5'9".
Assuming the inseam thing is correct, my feeling is that 175mm crankarms for a road bike would be a little bit on the long side. If it was for my bike, I'd go with 172.5mm.