Its late on a Friday, so I'm a little fried, but having gone through those calulations before I'm fairly certain you're missing things... I know I've seen far more exhaustive calculations than that, and its definitely been more than a factor of 1.6... its closer to 3.5x equivalent weight savings, although the actual number depends on how the car is driven.

I'm not questioning your math, or the logic, I'm questioning how it applies. Admittedly its been a while since I've studied this sort of basic physics, but something just doesn't add up in there. You're equating how much a given drop in rotational mass affects the equivalent mass of the entire vehicle, but thats not the point. The reduction in mass, as I said in my other post, makes its biggest difference in the amount of energy lost between the engine and the surface of the road during accelleration. When people say its the eqivalent of reducing weight by 4x the amount, they're not talking about mass, they're talking about the end result of accellerating the vehicle from speed A to speed B (whether a positive or negitive delta -- since lighter wheels help braking as well).

Again, *that* is where the benefit comes from -- if you are getting a few or five percent more power to the ground, not that the car itself is any lighter. Lessened mass at the wheels, however, would improve things like turn-in, probably closer to the amount you were calculating.

Thats no theory, its a fact. Thats why rolling dynos are not comparable between cars -- tire and wheel weight (and even things like alignment) make a BIG difference in the amount of power delivered to the road, and can make a 10-15hp difference *easily* in a dyno result.

Boston Audi Group Website