650cc wheels

The main reason for running 650 wheels is for aerodynamics. The 650 wheel has a smaller diameter than a 700 so the frontal area of the front wheel is smaller and it is more aero. The wheel spinning causes turbulance so the smaller the wheel the less turbulance. It would be better if you ran a 700 in back, it would be better for your gearing but I do not believe that uneven wheeled bikes can be raced because of the UCI. Years ago front wheels were were 24 inch but they felt that a 24 inch wheel though it had a smaller frontal area than a 650 it had to spin faster to cover the same distance as a 650 so it actually caused more turbulance. 650 wheels are also used for frames so that a small person can use to get a short top tube without having toe clip overlap.

Quoted post said:

Originally posted by pudster
The main reason for running 650 wheels is for aerodynamics. The 650 wheel has a smaller diameter than a 700 so the frontal area of the front wheel is smaller and it is more aero. The wheel spinning causes turbulance so the smaller the wheel the less turbulance. It would be better if you ran a 700 in back, it would be better for your gearing but I do not believe that uneven wheeled bikes can be raced because of the UCI. Years ago front wheels were were 24 inch but they felt that a 24 inch wheel though it had a smaller frontal area than a 650 it had to spin faster to cover the same distance as a 650 so it actually caused more turbulance. 650 wheels are also used for frames so that a small person can use to get a short top tube without having toe clip overlap.

Actually the 650 wheels on small bikes not only allow short toptubes,but get around other geomerty compromises that have to be made with small frame sizes trying to use 700c wheels.. Toe overlap is not necessarily confined to just smaler sizes with 700c wheels.