Got this from another forum
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Each 1 lb or rotational weight ( unsprung mass) decreased is almost equal to 6 1/2 lbs of dead weight in the car itself. (sprung weight)

Example: If a racing wheel is 39 lbs and my street wheel is 51 lbs, that is 12lbs less for one wheel,24 lbs less for the rear wheels, and 22 lbs less for the front wheelsfor a total of46 lbs less. Multiply that by 6.5 and that would be almost like removing 300 lbs out of the car itself. THAT's significant!

In simple terms f = ma Force = Mass x Acceleration

or Acceleration = force / mass

If the force is constant and the mass is reduced, acceleration is greater.

( Over-simplified terms here)

There are also calculations on wheel diameter and weight, minus tire diameter and weight.

So in short, smaller diameter wheels typically have less weight, In addition, weight that is closer to the hub center will allow rotationusing less force (horsepower).

Even if the overall diameter of the wheel is the same, the wheel with the smaller rim and weight closer to the center of the hub will accelerate faster. ( That may be why most drag wheels or 14" 15" or 16" rims.)

Each inch the rim is increased, the car looses about 4 hp, and each 5 lbs the wheel increases in weight, another 3-4 hpis lost.

In addition, braking efficiency and ride quality are both diminished as the wheel weight increases.

good stuff

nice info.

This is all very true. I noticed it markedly when I swapped out my 215/40R17 wheels and tires (wheels are 17", 14.1 lb Koseis) for 14" (or whatever) '92 Civic Si wheels and all-season tires. It was for a long-distance trip, and I wanted to get better mileage by driving on the skinnier, harder-compound Si tires. Even though the Si wheel/tire combo was heavier overall, because the weight of the wheel was concentrated more in the middle, the car accelerated much faster.

Believe it or not, the biggest difference in acceleration was from 80mph-110mph, and not from 50-80 or anything else where traction was not a factor. I believe this can be explained by EK= 1/2mv^2 (kinetic energy = 1/2 mass X velocity squared). The amount of energy it takes to triple the velocity is 9 times (because velocity, 3 in this example, is squared), but the amount of energy it takes to quadruple the velocity is 16 times!

So I think it goes like this: (j here is used as a representation of units of energy, like Joules)
20-60 MPH: 9j energy difference
20-100 MPH: 25j energy difference (5 squared)

So the energy difference between 60 mph and 100 mph is actually 16j units, not the expected <4j. So the faster something is moving/spinning, the more energy it takes (exponentially) to increase its velocity.

Is this right?