Originally Posted by
Retro Grouch
How accurate to you need it to be?
If you set the computer to the nominal tire size, it will be about as accurate as a car odometer. That's accurate enough for me. If you roll out your wheel, you can gain some increment of accuracy. Some riders roll out and average multiple wheel revolutions for even more precise accuracy. Unless you are a person who pursues accuracy for it's own sake, I don't see that it makes a lot of difference.
Car odometers are supposed to be, by law within 5% which means a car with 100,000 miles on it, could read as low as 95,000 miles or as high as 105,000 miles. I measured out both the road bike and the mountain bike, the road bike measured out 2100mm where as the chart that came with the computer read 2124 a difference of a little under 1.2%. Which is close enough.