Originally Posted by rlong
I cannot imagine that crankarms 5mm's shorter will make a noticeable difference, but I'm not sure.
My tandem had 175s front & rear. That 5mm difference in each crank made a difference to me -- it brought on knee pain that I hadn't had before, and that went away when I put 170s on.
Also, note that if you are adjusting saddle height to the same full leg extension at the bottom of the stroke, going from 170mm to 165mm results in a 10mm relative lowering at the top of the stroke. (When you put the shorter cranks on, the seat needs to go up 5mm to accommodate the original leg extension at bottom, which, combined with the 5mm shorter "reach" of the crank at the top, makes a 10mm net change at the top.)
Apparently, sensitivity to crank length varies a lot with the individual. I still have the 175s for the stoker. My daughter uses crank shorteners, but my adult stoker -- who's probably about an inch shorter than me -- can ride all day with the 175s, spin them upwards of 120rpm, and not blink an eye.
-Greg