...from another forum.....

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.

Soin 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... I put a link to this thread in the wheel/tire faq

 

Thanks; it's nice to see numbers instead of just general theory when it comes to wheel weight.

 

As much as I hate replying to a year old dead thread, this one belongs at the top. Those numbers are impressive, and new to me!

On a side/hijack question regarding unsprung weight. I have 13" steelies and stock tires now. Whats the lighter combo? 13" aluminum wheels or 14" aluminum with stock sized (comprable) tires?

 

Here's how I figured out what change in weight would occur when I plus-sized:

First, find out how much each wheel size weighs. Next, pick out a matching tire for each wheel (assuming you know the correct size tire) at tirerack.com. If you don't know what the correct tire sizes are, you can enter your car year and model in the "wheels" category. Plus sizes will be shown along with the stock sizes. After you pick out a tire, the specs section will show you tire weight. Once you know the weight of each of the two different tires, you can add up the total weight of each tire/wheel combo to compare.