Quote Originally Posted by Savra View Post
The crank on my road bike is 7.5" and on my Surly 7".
Take a look at the back sides of the cranks - the sides towards the frame. There will inevitably be stamped a length. This marking will usually be near where the pedal attaches. It'll be just a plain number like 165, 170, 175, and etc.


While you're checking the crank length, check something else too: Turn the crank until one crank arm points up along the seat tube. Measure the distance from the seat tube to a convenient prominent location on the pedal. Now rotate the cranks so the other crank is pointing up along the other side of the seat tube. Measure the same distance on that side.

Your two measurements should be identical. However, some bikes ship from the factory with the pedals not centered! Most people seem to be able to adapt without noticing the off-centeredness. However, your joint issues might make this an issue for you.