I am looking at 3 sets of 17s .. one weighs 18 pounds, the other is like 19.5, and the other is 21 pounds. How much will that kind of a difference in the weight of the rims impact the speed of the car? How bout approx how much time would it take off your quarter?

 

Its not neccicarily the Weight of the rim cause they seem like light 17's, its the rotational force thats needed to turn the extra wheel, then if you get 17x8's the weight is farther away from the car so that plays a factor. Ive heard for every inch of upgrade it takes away 2 wheel hp which is pretty significant...wieght does play a factor but for 17's you dont have a worry too much
Once you get 18's then youll start to worry about a big loss

-Matt

 

like matt said, 17's are not a big worry, its the weight and the overall dims of the rim that make the diffrence, however anything under 20lbs. is considered pretty good. and those 17's are pretty light. Stillen quoted me 32 lbs for the Momo Arrows (17x8).
good luck

 

For every pound you take off your rims, that is equal to taking out 8lbs of dead weight in your car.

You will also have to watch the offset as that will play a roll in rotating mass. A lighter rim with a crazy offset might end up hurting you then a heavier rim with the correct offset.

 

9 pounds of UN-SPRUNG Weight to be exact. Un-Sprung weight is anything NOT supported by the springs/suspension.

Theoretically, if I had MOMO's at 32 lbs each, then put on my Volks at 15 pounds, I have a savings of 17 pounds per wheel (Total of 153 lbs of un-sprung weight) mulitply that by 4, and you have a total of 68 lbs of wheel weight reduction and 612 lbs of unsprung weight. Rotating mass fits into that equation too....

 

I've been trying to figure something out...

Do larger/heavier wheels actually cause you to dyno LESS, or is it just the extra weight that slows you down?

I could have sworn I read an article where all they did to this car is go to lighter wheels or something and it actually dynoed at 10 whp more or something. But maybe they meant that the effect was like-10whp from the rotating mass reduction and not that the car actually gained power...

I'm thinking now that heavier or lighter wheels will not affect dynos, but *will* affect your overall acceleration rate.

Any thoughts?

 

Both the weight and rim size plays a part in vary HP differences. The differences is a matter of a few HP. I know SCC tested the same rim on a Honda but in 2 different sizes. The difference was a matter of 2-3hp from 1" size.

I know SCC had a few articles regarding this. If I can find it, I will quote from it.

BTW-Don, I thought a gallon of gas was 9lbs? Oh well...

 

Nope, a gallon of gas is 8 pounds.

 

bottom line get those 18Lb wheels that would be the wisest decision made.

 

I'm no expert by any measure, but I would speculate that heavier wheels would cause you to dyno less. I don't really know how dynos work but I imagine they measure how hard the car is turning the wheels. If the wheels where X pounds heavier, it would be that much less HP that's transferred to the ground.

A parallel situation could possibly be to dyno an automatic vs. a 5spd. If the auto drivetrain loss is ~24% and the 5spd is ~18%, than would the 5spd dyno more because more power would be getting to the wheels?

 

A gallon of gasoline weighs 6-6.5 lbs. Water is 8lbs, gas weighs less.

The difference will not be dramatic, but you might notice it a little bit if you are very observant. In changing from a 37lb wheel and tire combo to a 30lb wheel and tire combo, I've seen about .1second and 1mph improvement in the 1/4 mile. Significant, but not very dramatic.