For every 1lb of unsprung weight saved, that's equivalent to 7lbs of total weight savings. So, if you have 16lb rims in place of the 24lb OEM, then:
24-16 = 8*7 per wheel = 56*4 = 224lbs effective weight saved by reducing wheel weight.
Kinda crazy, but it works. That's why F1 and other racing series' tire and wheel combos are so light...
Unless someone wants to trade me a nice set of 16-18lb 17" rims for my stockers, I will not be buying any new rims for a while...(pissed) Just ask my wife!(poke)
Daniel
This is unfounded.
Why did you use this equation?
Granted, I will absolutely agree that rotational, unsprung mass is important to reduce, I disagree (politely) with your equation.
Unfortunately, it is very hard to equate rotational mass with static mass equivelants. That is because a wheel (or anything else that spins) has a different concentration of mass throughout its radius. This means that each wheel design has a different rotational mass equality.
Look at it this way: A wheel that weighs 22 lbs, but has 90% of its mass in the center of the wheel (not possible, but play along) will behave differently then a 22 lbs wheel that has 90% of its weight in the rim section.
One thing that is true is that the total weight of the wheel, regardless of where the weight is placed, will have an effect on the unsprung weight. This will change the "feel" of the steering and other effects, and make the car behave a lot more different (is that an actual phrase?) from sprung weight changes.
These changes are really noticeable on a motorcycle, but a car can be affected by these gyroscopic effects as well. The total "weight" equation, however, is not a solid exchange. You can say without any doubt that reduction of weight is paramount to enhanced performance. I also would say that I'd prefer a wheel that has less weight on the rim.