2007GT/CS

I asked this question over at the f'nsweet website as I could never get an answer from Roush. 34 lbs was what I got from the members there. Nice as they are, that removed these wheels from consideration for me. I'm leaning towards the TR Motorsports MT1s at this point (19.5 lbs).

jayel579

The basic equationis that1 lb of unsprung weight is equal to about 10 lbs of sprung weight. Now if you go from the stock wheels of around 25 lbs and go to a chromed 20" wheel that weights 32 lbs, you are talking about weighing down the car by an extra 280lbs. I haveto think that is pretty significant thoughI seriously doubt anyone would race on a set of 20" chromes wheels.

Red06

I save ten pounds per wheel and tire with my Enkei RS+M and Yokohama Neova setup over the stock bullets and BFGs. I don't remember the gross weight of either just the ten pounds difference. Theimprovement in acceleration is VERY noticeable with the Enkei/Yoko setup.

The rims are not the only component in the equation... Check the Tire Rack site and you'll see therecan bea big difference in the weight of tires as well.

Joe

Norm Peterson

Not even close. 1 lb unsprung= 2 lb sprung, maybe. Enough to show up in the clocks, sure.

2007GT/CS

My turn. I always understood it was 1:6 and that was a comparison between reciprocating vs. non-reciprocating weight. E.g. every pound you remove from the drive line is like removing 6 from the overall car. That's why people put in stuff like aluminum driveshafts. The car gets much quicker than the simple weight reduction accounts for (say between the 42lb stock two piece and a 16 lb replacement = diff 26lbs but then multiply by 6 = 156 lbs -- that's where the .1-.2 tenths in the 1/4 comes from).

You would think this would hold true all the way out to the rear wheels. The lighter I can make those guys, the less inertia I'm overcoming with my power.

Obviously that only explores one aspect -- the other being the sprung/unsprung effect of weight on handling characteristics (q.v.). I was really surprised that Roush wheels weigh what they do and that things like Steeda UltraLights ain't that light.

I want some Fikse

Blacksmoke

I called Roush and after a ton of asking I got a shipping wieght of around 34pounds which is what they said it would be around for the wheel.

I bought these things about a year ago. Man I can't BELIEVE that a 18x10 weighs THAT much.
I actually could not feel a difference in acceleration then.

So about how much time am I losing in the quarter with these dam things?
Enough for me to lose against a stock 06 350Z?

Sam Strano

Shipping weight is just that, in a box, packed and as it weighs to UPS or FedEx, etc. That's pretty freaking heavy even if you take 5 pounds off for packaging. A Volk RE30 (which is very light) and a Hoosier tirecome to just about51with the tire mounted!

Sure it's costing you some, not a ton, but some. Easy way to know it toget on a chassisdyno and try lighter wheels (stock maybe) vs. what you have. I've seen tests of big brake kits on FWD car (and bit is relative, usually around 12" on those) where they lost double digit wheel HP. And remember you have to turn 4 of 'em not just two, it's simply a measure of what you arelosing

Norm Peterson

2007

There's a difference between what is true in general terms (rotating mass has a greater effect on acceleration than mass that's fixed to the frame) and the actual numbers (which can be calculated based on material density, part geometry, and the rotational acceleration of the part).

The rotating mass effect depends partly on the relationship between the rotational acceleration of the thing you're looking at and the acceleration over the road of the car as a whole.

Without going too deep into the math, that depends on where along the drivetrain the part in question lies, as that determines how fast the part rotates relative to some measure of road speed. Remember that you have gear reductions in at least two locations IOW, you could say that wheels, tires, rotors, axles, and ring gearhave one factor, the pinion, driveshaft, and output shaft of the tranny another, and the input shaft, clutch assembly, crank, and harmonic balancer a third. There are others, but the masses involved are small and their effects can be neglected. So no one factor can possibly describe what's going on over the whole drivetrain. 6:1 or even 10:1 might well be an appropriate guideline for the flywheel, but it isnot applicable to the tires and wheels.

The rotating mass effect of a generally circular item also depends on the radius of the rotating mass (the radius thing is a 'squared' term when you compute mass moments of inertia). But that can be looked at as a separate piece of the puzzle.


Norm