SCott5

iTrader: (40)

Okay. Im in the boat of either 17x4 or 15x3.5 for the front of my car. I like the look of both but I am more geared toward the performance aspect of this and I am going after a pretty tall order over on the sci n20 record so every ounce really does count and every .01 does too. So I am looking at the rotational mass of both. So my question is. Given the same wheel for ex: Alumastar, Would one have more than the other, Does the weight of the wheel or tire matter more or just the total weight of them both combined? SAY they both weigh (total wheel and tire) the same would they give off the same rotational mass? I tried searching but most things I found were comparing full size wheels to skinnies

99Bluz28

iTrader: (35)

I believe you'll have to factor in the wheel and tire together. Since the 15 x 3.5 will have the lightest wheel/the heaviest tire, and the 17 x 4 will have the heaviest wheel/ lightest tire. I would think that if the 17" and 15" wheel tire combo weighted the same and had the same tire outside diameter it would probably be close but the advantage would go to the 15" wheels since most of the mass would be closer to the axis of rotation. I'd probably go with the 15's and go with a smaller in diameter tire which will also cut down on rotational mass(if possible).

This might help:
http://en.wikipedia.org/wiki/Moment_of_inertia