Linear kinetic energy from wheel's center of mass traveling horizontally: 1/2 * mass * velocity^2hill wrote:greenleaf - you are partly correct ... but reduction in wheel weight is actually even better than linear. The formula relating to this (on some tire/wheel web sites) is described as an exponential factor.
Rotational kinetic energy from wheel spinning: 1/2 * inertia moment * angular velocity^2
Inertia moment is a function of wheel mass and geometry (linked from wikipedia since there's no point in redrawing it)
To translate for non-mathematical types: Reducing mass at a distance 2R from the axis will decrease inertia 4 times more than removing the same amount of mass at distance R. Simply put: Get the mass off the edge of the wheels!
This is an excellent argument for getting low profile tires and decreasing wheel radius as a whole, although that may impact your top speed and throw your speedometer off more than it already might be.
Of course, it's only worth it if you're changing speeds a lot. Under constant speed conditions reducing wheel mass will have the same effect as reducing the mass anywhere else. Not worth as much for highway commuters as it is for city commuters.