Originally posted by chemguru:
Pi aren't circle... PiR^2.
Sorry... 
:rolleyes: Err, Pir^2 is AREA of Circle. :rolleyes:
Circumference is Pi x Diameter or Pi x Radius x 2
Another shortcut is to put some paint on the tread of the tire, Sit on bike and roll forward, putting 2 paint marks on ground. Measure distance between marks. This gives you Rolling Radius of tire, which will make your computer that much more accurate.
