Originally Posted by Retro Grouch
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.
I was going to say the same thing. I am 5'10" with a 32" inseam and on my Salsa project decided to go with a 172.5 crank rather than the 175 that is on my current bike. I have been talking crank length with my father as weel as he is trying to buy a new bike and he (although just a bit shorter than I) is going to go the opposite wat, from 172.5 to 175. His comment on it was that even in HS when he ran track he always has a long stride and that the longer crank on a couple of test bikes just felt better to him. I had never heard this topic discussed in those terms and it added some validity to my choice of shorter cranks as I know that I prefer a shorter running stride and spinning on a bike.