Figuero is right on.

In addition to handing (as Greg correctly mentioned), there is another effect of the rotational unsprung weight (wheels, tires, brake rotors, half shafts, etc) on acceleration and braking.

The absolutely correct term that should be used here is unsprung mass but we are not going to space or another planet so let's be partially wrong by using weight. Please do not comment on this part because the general public is so confused on this.

The equivalence of 1 lb of rotational unsprung weight from EACH wheel is 2 lb of static weight is actually the worst case scenario. However, it is not too far from the real value of 1.7 lb to 1.9 lb, depending on wheel design (weight distribution).

In some old hot rod magazines, they quote numbers like 1 lb of wheel weight reduction is equivalent to 6 lb or 8 lb of static weight. That is right but often interpreted wrongly. There are 4 wheels in a car so if you reduce 1 lb from each wheel (and 1 lb is equivalent to 1.5 lb or 2 lb of static weight) and that is why they have the 6 lb or 8 lb numbers. So 1 lb of reduction in wheel weight is still equivalent to 1.5 lb or 2.0 lb reduction in static weight. There are just 4 wheels.

Here is an ideal case but it help understand this situation.

Let's say someday they design a (super strong) plastic wheel that is extremely light (assume zero weight for this discussion), then the wheels weight would have no effect on acceleration.

Now why the 1.5 lb or 2 lb numbers? First of all, the 1 lb in the 1.5 or 2 lb is simply the weight of the wheel itself. In another word, if the wheel slides (no ABS, LOL), it would behave just as the true weight of the wheel.

When the wheel rotates, then additional energy is required. The effect is the same AS IF the wheel is heavier now.

If the wheel WERE a disk, i.e., mass uniformly distributed across everywhere, then the effect is 1 lb for 1.5 lb. I am not going to show the calculations here but the moment of inertia for such a disc is 0.5MR^2 and that is where the extra 0.5 lb comes from. To get the full details, we would calculate the motion of the wheel as a combination of a linear (straight line) motion and a rotational motion. The angular speed (rotational speed) is related to the car speed (linear speed) and the radius of the wheel.

If the wheel WERE a hoop, i.e., all the mass is on the rim, the part that touches the tire, then the effect is 1 lb for 2 lb. (The moment of inertia for a hoop is MR^2 and that is where is extra 1 lb comes from).

Most modern alloy wheels are neither discs nor hoops but they are closer to hoops than discs because the modern alloy is very strong so not much weight is required between the center of the wheel and the rim of the wheel. So that is why 1 lb is more like 1.7 lb or 1.9 lb, depending on wheel design.

Now the lighter the brake rotor, the faster the acceleration. It has the same effect as wheels and that is why car makers are making the rotors thinner (lighter) and thinner (lighter).

Although the crankshaft pulley and others are not technically unsprung weight, they do have similar effect from an energy consumption point of view.

In the other W210 forum, Figuero and I had some fun with a vendor who claims (big) power increases with their crankshaft pulley.