Originally Posted by
BlazingPedals
Just as a ballpark number, though, a 28mm tire on a 622 rim would be 622 + (2x28) = 678mm diameter. Circumference is pi(d) so 678 x 3.14 = 2129mm. Or, if your computer wants cm, then it would be 213cm. That would assume that the tire was a true 28mm tall when you were on the bike and the tire was squished down. Various factors could affect that number by 5 or 10.
edit: Yes, the tire should have a load on it when you're rolling it out. If you want it to be accurate.
I think you are wrong on this. Even though squishing the tire deforms it, it shouldn't affect the overall circumference and thus shouldn't affect the overall distance traveled per revolution.
Last edited by thomasbrent; 02-16-13 at 10:44 AM.
Reason: Used "over" too many times.