| Here is a different (and maybe simpler) way of getting to the same answer...
If the weight of the wheel acts as though it was all lumped at a radius of 9", then the rotational energy is the same as if the wheel was moving in a straight line at the speed of a point 9" from the center.
If the wheel radius is 12", then this speed is 9/12 = 75% of the speed of the vehicle.
As energy is proportial to speed squared, the rotational energy of the wheel is 56% (75% x 75%) of the linear energy. i.e. A 1 lb saving from the wheel is equivalent to a 1.56 lb saving from the car.
2007 DS/W MCS LSD, sport suspension, Enkei RPM2 wheels
2002 EB/W MCS Sport package, Rogue intake, Borla exhaust, 15% pulley & Madness sway bar | 
