Originally Posted by
mjoekingz28
I know, but maybe I didn't have the stem perfectly at a right angle to the ground. The best way I see is to mark the tire with chalk, white out or paint and that would be perfect, but quite the hassle. I don't see how it could improve on taking the diameter of the tire X3.1416.
What degree of accuracy do you have in measuring the diameter of the tire? If you just take the mfg word for the tire diameter, I suspect you will not even be close.
It's quite simple and very little hassle to do this right. Make sure your tire pressure is up. Put a healthy dot of paint or whiteout on the tire. Get on the bike and roll (in a straight line) at least one complete revolution so that you have at least two points to measure. Take the measurement in inches and multiply by 25.4 and you have the number to plug into your unit. Using 26 x 3.14159 is only close in the horseshoe/hand grenade department. But if that's close enough for you, so be it.