Quote Originally Posted by makbike View Post
I'm curious as to why one should not use the wheel size charts to program their computers? Are the charts not accurate?
Because they will depend on the size of the tire, some are deaper than others. Also on the wieght of the rider and the amount of air in the tire.
I have a Giro 20, I always do the roll out method - sit on the bike, line up the valve with a crack in the side walk and roll 1-3 circles, mark the spot and measure it. Then convert to cm from inches if, like me, you only have a tape measure that does inches, and divide by 3.
That said, though, my memory is that I have mine set at 1923, but I have a 26" Conti GP 3000 on my rear wheel. If you've got the Kenda's that come stock, it might be a little bigger.
The fact that it's a Giro 20 won't mean too much to most on this forum, what's important is that it has a 26" wheel (vs 650), what is that, a 571? For more info than you ever wanted on the topic, check out Sheldon Brown.
http://www.sheldonbrown.com/tire_sizing.html