964C4

I am not talking about drag racing, but general acceleration of the car

My stock wheels weigh:
Front 22 Lbs. 8 Oz.
Rear 27 Lbs.

The possible replacement wheels weigh:
Front 25 Lbs. 13 Oz.
Rear 33 Lbs. 1 Oz.


I am especially concerned at the increase of 6 Lbs. at each corner at the back

What do you guys think ?

mdrums

On the street you not notice anything big. On the track after many years experience you can notice a difference in handling

sjfehr

I'm looking at finally dropping the hammer on a dedicated set of wheels & r-comps for autocross on my 986S. It'll cost an extra $700 to shave 5lbs/wheel from the cheaper wheels, though. Will the difference be measured in tenths or hundredths?

aj986s

Wheels are part of the unsprung mass of a car; basically the weight that's not held up by the car's suspension. Less unsprung weight helps handling, and if part of the rotating mass, like the wheels, also has some affect on acceleration. But the greatest affect to acceleration is probably attributable to the unsprung weight factor. Rule of thumb is that 1 pound of unsprung weight is equal to 6 pounds of sprung weight (some say even more). Looks like you have about 19 pounds to total added wheel weight (unsprung), which would translate to about 120 pounds of additional overall car weight (sprung).

911SLOW

Olaf Manthey explains in an interview : “Removing 33 pounds of unsprung weight at the wheels is equivalent to losing 198 pounds from the body of the car, as a 1:6 factor has to be applied when the car is moving and that weight becomes mass. In fact, we are conservative with the 1:6 ratio, as Porsche considers it to be 1:7.

John

aj986s

Thank you for the corroboration..........

..AND THE AVATAR(s)!!

RollingArt

Probably not.

The wheels affect on acceleration is due to it being rotating mass that must be accelerated and decelerated. Nothing to due with it being unsprung.

The fact that the wheels are unsprung weight affects the cars HANDLING only.

Imagine adding 10 lbs to each caliper. That is adding unsprung weight. But it's affect on acceleration will be the same as adding 40 lbs to your passenger seat. It's just another 40 lbs you need to get moving.

Now add 10 lbs to each wheel. That weight not only increases the amount you must accelerate by 40 lbs, you also need to get that extra weight spinning, which will require even more power than adding sprung weight (pass. seat) or stationary unsprung weight (calipers).

Hope that came out somewhat clear.




Phil

RollingArt

“Removing 33 pounds of unsprung weight at the wheels is equivalent to losing 198 pounds from the body of the car" (911SLOW)

That's 33lbs of unsprung weight at the WHEELS. The reason for the 1:6 ratio is the wheels must be SPUN UP to speed. Nothing to do with it being unsprung weight.

The fact that it's unsprung effects handling only.

Losing unsprung weight at the calipers is 1:1 ratio to losing weight off your gut.




Phil

aj986s

I see what you're saying. And I'll be the first to admit I don't completely understand all the science & physics behind it. But I've read more than once that unsprung weight does have a 6:1 weight factor in terms of how it affects the overall car (I think the first time I saw it was in Fred Puhn's "How to Make Your Car Handle"). Whether it was brakes, spindles, wheels, etc. didn't matter. But I do agree that wheels and rotors do also have a rotating mass issue. Likely the 6:1 factor is an average, and maybe even skewed when you consider that most of the unsprung weight is probably associated with rotor, wheel & tire.

911SLOW

^
Exactly but why you quote it? Olaf said at the wheels : )

Edgy01

Lesser unsprung weight also translates to an increase in the nimbleness of the car on the road/track. If you're a snow skier you can recognize that as you are working down a mogul field you can field how important extra weight can affect your ability to turn and deal with bumps--less weight to rebound, etc. You can definitely affect the handling of these cars if you aren't paying attention. For example, between lighter forged wheels and PCCBs, you can take quite a bit of weight off, which translate into the different feel you will experience on the road.

Mspeedster

From your other post about pics of the Sport Classic wheels with Meteor Grey, I assume the heavier wheels in question are the 911 Sport Classics. I too would very much like to get a set of the Fuchs style wheels, but the heavier weight is a serious consideration for me.

I do know from my own first hand experience that lighter wheels improve the handling, which can be felt on the street. Porsche engineers did their homework when they picked the original 997.1 "lobster claw" wheels as standard for the S models, as they are the lightest OEM Porsche 19" wheels for the 997.1. The Sport Classics are more for "show" and while I love the look, I'm concerned about how the added weight might affect the handling enjoyment that I derive from my car.

964C4

Correct what you say !

The Sport Classics are the wheels in case, but after checking the weights, they are too heavy !

And Fuchs Performance USA has their own Fuchs wheels in very simmilar finish (even nicer to my eyes) and with nice light weights, but at $ 5,100.00 for wheels only !!!

signature65

^^^^^ Now those Fuchs look most like the original ones......the sport classics just have that too glossy/modern look to them.

Edgy01

One of these days I hope to be able to provide weights on the Fuchs USA wheels. Although expensive, they will weigh less because they are one-piece drop forged. Cast wheels tend to be heavier as they must increase wall thickness to enhance strength.