This is more of a technical question...

I was always under the impression that going to a larger diameter wheel will slow one down due to an increase in rotational mass since the mass if further out? (sorry, physics is not one of my strong suits). Obviously a lighter wheel has less mass and I suppose one should theoretically be able to go faster. If the diameter of the wheel is increased, will lightening the weight offset the disadvantage of going to a larger diameter wheel?

I recently put on the 17" Mugen MF-10 wheels from my 16" OEM wheels fully expecting the car to slow down a bit given the larger diameter. To my surprise, I felt almost no difference. My butt dyno thinks the lighter Mugen rims makes my car run faster, but I'm sure that's more bling (psych)-related than actual improvements.

what gives?

 

As long as the total amount of unsprung weight is reduced, the car is better off. Diameter does not matter (however, typically more weight comes with larger wheels).

Edit:

Those concerned with weights of their wheels or looking at aftermarket wheels may want to bookmark this site: http://www.wheelweights.net. It has just about everything of that concern.

 

If you are running lower profile tires, then your overall diameter would be the same as the 16's with taller tires.

 

Many quality 17" wheels weigh less than stock 16". When you reduce rotational wieght, you can accelerate faster. Changing the diameter only matters when you are talking about the overall diameter of wheels and tires together. A larger than stock wheel with the same tire profile will increase your overall diameter. Using a 16" wheel with a lower profile tire than stock would decrease your overall diameter and changes your final drive ratio (for the better).

 

Kinda right. "rotational acceleration" = torque / moment of inertia (i.e. "equivalent rotational mass"). I'm really hacking the definitions now. Moment of inertia depends on the actual mass ("weight") and it's distance from the center of rotation. So more mass increases moment of inertia, but so does the increased diameter, i.e. mass farther away from the center of rotation.

So a wheel with the same mass but bigger diameter is slower, but if the bigger wheel is "lighter" it can be "faster" than the smaller wheel depending on its weight distribution.

 

thanks for the quik'n'dirty physics lesson. that wheel list is pretty comprehensive. I would have never thought that a 3.5 lb difference front and 2.5 lb difference rear would make much of a difference.

 

don't forget moving to a bigger rim adds more tire weight as the tire is bigger so weight lost on the rims is probably gained back from tire. I just have experience with my Integra going from stock 15's to aftermarket 17s. Weights for the 17rim was a lb or so lighter, but I was much faster with the stock 15s

 

When going from a 16" wheel to a 17" wheel on the S2k, a lower profile tire is generally used. Therefore, the tire may or may not be heavier.

 

I think you meant to say that moving to a bigger rim subtracts tire weight (given the same unloaded rolling diameter).

Good point, by the way.

 

Hopefully he was trying to refer to an increase in "width."