Diabolical!

When I bought my new-take-off machinefaced wheels off of ebay, they came in two boxes, each with two wheels and tires inside. The shipping company marked each of the boxes as 83 lbs, so I figure the machined face wheels with pirellis weigh about 41.5 lbs on each corner (give or take).

steelcomp

My polished 18" Bullits weigh exactly 50# with 1/2 worn Nitto 255/45's on them. In comparison, my new wheels and tires weigh 43 lbs, and that's going to a 275/40 tire on an inch wider rim. The 7lbs per wheel is definitely noticeable in the seat of the pants.

steelcomp

With rotational mass, simply put, the further you are from the center, the more material there is trying to travel a greater distance in the same amount of time as the material closest to the center, and that takes more energy. The more weight you can remove from the furthest distance out from the center of the rotating mass will yield the most change. The biggest change you can make is lighter tires, given everything stays the same AFA rim diameter and width. If you look at tire specs, there is a big difference in tire weights between mfgrs. Pure racing tires are even lighter yet (as per Norm's comment about racing tires being shaved) and the biggest reason you can't run them on the street...they're just too thin.Next is the wheel. Depending on the wheel's construction, (one of the reasons to really research wheels before buying) there can be a large reduction in the weight of the outer rim itself, which is going to be most beneficial in performance. The weight closest to the center of the wheel has the least effect on the rotational factors of performance. Static weight is just that, and only benefits the reaction time of the suspension to vertical movements, and to lower the overall weight of the car, but that's insignificant when we're only talking 20-30lbs net. Reduction of overall rotational mass as unsprung weight helps, but if you can focus on getting the lightest possible outer weight, that will be the best scenario.

Argonaut

Wow - never thought I'd attend math class on MSF.

Here's my seat of the pants: I have a set of 17X9s that weigh 18lbs apiece. I was expecting to feel something...some small improvement in feel or butt dyno. Nope. I agree with what Norm said earlier in the thread - it would take a very sensitive driver to feel any improvement in acceleration, all other things equal.

steelcomp

What tires are you running? What was the previous set up?

Argonaut

My tires on the 17s are Falken Azenis 615.My 18s are American Muscle bullitswith Sumitomos.

Don't get me wrong - the carhandles WAY better with the 17s and Azenis. Its the acceleration where I don't really notice a difference, like in day to day driving.

steelcomp

Here's my new wheels and tires. I had actually started a thread with this since we were talking about tires and handling, but it mysteriously disappeared.
The rimsare Volk RE30's (18 x 9.5 x 52mm offset) with 275/40 Michelin PS2's. The rims are 16lbs ea., and the tires are 27lbs. I had the factory 18 x 8.5 polished Bullits with 255/45 Nittos and I could definately tell the difference. The PS2's are awsome.
(Thanks Margarita Girl for the pic effects )

Sleeper_08

steelcomp

Any signs of rubbing on full lock?

Is the car lowered?

Thanks.

steelcomp

No rubbing anywhere, even during full lock bumps, and yes, it's lowered. Front fender lip is 27" from ground.