Originally Posted by cyccommute

A 26" wheel (559mm ISO) and a 700C (622mm ISO) (aka 29er) and a 27" (630mm ISO) aren't 26", 700mm nor 27", respectively. A 26 inch rim is really 22" in diameter. A 700C is really 24.5" in diameter. The 650B (aka in 'Merika as the 27.5er...dumb! Dumb! Dumb!) is really 23" in diameter. The sizes come from the outside diameter of a "standard" tire mounted on the rim. If you do the math, you'll find that that "standard" tire is kind of goofy too. For the 26" wheel, the tire is 2" in diameter. For the 700C, the tire is 39mm tire which is very wide for any modern road wheel.