Originally Posted by
The Hansenator
Thanks, it sounds like I shouldn't worry about it unless it becomes a problem.
Both bikes seem to be the right frame size and, as far as I know, have the original cranks. The 170 cranks are on an old Schwinn Le Tour which is about 20 years older than the other bike.
There has been a trend over that period of time to put longer cranks on the same "size" bikes, but it has usually been limited to a 2.5 mm difference. I suppose 5 mm longer on the same size frame isn't outside of the general range of the trend. One explanation is that 170 mm cranks on road bikes, esp. lower end ones, may have been standard at one time no matter the bike size. Now it is much more common to have cranks sized proportionally to the frame size. From the mid-level to upper end of frame sizes, that could make for discrepancies like the one you have observed.