dustinr

What's the deal with Porsche wheels? Why 19" & 20" wheels? 18's clear the brake calipers just fine and they weigh a whole hell of a lot less. Is it just for the look? I've noticed since I bought a Porsche, that Porsche people must care more about look than they do function. It's almost impossible to find light weight wheels for a P-Car and when I say light weight I don't mean 20lbs front and 25lbs rear. I mean 18lbs front and 20-21 lbs rear. I see lots of trick looking, "2 piece," "3 piece", "forged," wheels and they cost an arm and a leg yet they weigh more than the super heavy replica wheels that are for sell all over ebay. And when you do find a really nice looking, light weight wheel, it costs upwards of $1,500 ea and closer to $2,000 ea. Do Porsche people not even care about unsprung weight and rotating mass and how that effects handling, performance and horsepower? I've been trying to find a cool, light weight, 18" wheel set for my turbo and it's impossible to do it at a reasonable price. I've found tons of great, light, 18" wheels but they never fit Porsche's. OZ Ultraleggra, good light weight wheel in an 18" size... doesn't fit a Porsche (18lbs), you have to step up to the 20" Ultraleggra which now weighs 23 lbs front and 26lbs rear. stupid! That 5lb per wheel difference equates to roughly 40+hp and much better stopping, and handling...yet Porsche now equips all of their cars with these massive 19" and 20" flywheels because they look cool. Dissapointing. Of course I can always drop $15,000 and buy a set of Dymag's or Neez Mg's... which weigh 2 lbs less than a $400 OZ Ultraleggra in 18" ...more for less... a little less... rant over.

Edgy01

Porsche continues to move to larger sizes in order to extract the maximum performance capability from the car. Their suspensions are designed around the tire technology of today. Equally, brake dimensions are growing to keep up with the performance potential of these cars. I don't even believe I can put an 18" wheel on my car because of caliper and rotor clearance issues. As wheels grow in size along with tires we are not seeing a reduction in their weights. It's contrary to physics. Porsche is making progress in other areas to reduce unsprung weight, although most American buyers will never purchase that option for fear of sticker shock (PCCB).

mooty

fikse
bbs motorsport E88
champion
hre competition series
jong bloed
ccw

you are not looking at the right places.

dustinr

How big are the brake discs on the 997? Are they 15"? There again, which came first, the larger brake discs and calipers and therefore the 20" wheels or did the 20" wheels come first and they needed the larger discs and calipers to get the same stopping power? I think the latter is true.

I'll admit they look cool, but there are reasons I'm not a fan. One, you have to run very short, rubber band, side walled tires... this puts more emphasis on the cars suspension, which will mean suspension settings will now be more important and bad settings less forgiving. Two, in order to keep from damaging the wheels with every bump and hole in the road the wheels have to be made very beefed up which means...lots of weight.
Then there's the fact that the diameter is bigger and now the mass has moved farther away from the axis of the wheel. Here's some physics plagerism...

Let's have a look at some basic calculations:

Any object that has a mass and that moves at a velocity has a certain energy, which is coming directly from your motor. If you move a wheel at a certain speed (no rotation of the wheel ) the energy can be calculated using the following formula:

E = ½ m v2

m being the mass and v being the velocity at which the wheel moves.

Once the wheel turns, the total energy is made up from two components, namely the translational (moving) part and the rotational (turning) part. The new formula looks like this:

E = ½ m v2 + ½ J w2

J being the Rotational Inertia and w being the Rotations per second.

The rotational Inertia is made up of the mass of the object and the distance it is away from the rotating axis. Remember the flywheel effect: the further the mass is away from the axis, the more energy it takes to accelerate or brake it. If the mass is twice the distance away from the axis, it will require 4 times as much energy (or engine power) to accelerate and brake.

Example :

0.1 kg (or approx 1 N) which is 20 mm away from the axis will have a Rotational moment of Inertia of 40.

If you have the same weight 40 mm away from the axis the Moment of Inertia will be 160 (factor of 4).



So how does this exercise look when applied to wheels?

The weight of the wheels is not the only consideraton: what is much more important is the Rotational Inertia of the wheels, namely how much weight is close to the axle and how much weight is far away from the axle.

How do wheels affect your handling?

The lighter the wheels, the less your un-sprung mass. This means that your suspension has to work less to dampen the wheels. This will result in less energy and less power being consumed from the engine.

It is more difficult to move or steer a rotating mass than a is stationary mass (try to move a spinning bicycle wheel ). If you reduce the mass and specifically the rotating inertia , the force required to move or steer the mass is reduced significantly.

So logically, the only advantage to larger wheels is looks.

Look at F1 cars... they run 13" wheels and huge sidewalled tires and still manage 5G's in the corners, although if they were given a choice I think they would increase their wheel size some to reduce that huge sidewall so as to decrease some tire deflection, but there is a point of diminishing returns....

Thanks for the wheel brands, I'll check them out.

cole328

Plus, 19"ers just look sweet............

morganabowen

Not to mention the cost of 19 & 20 inch tires as opposed to 18" tires Just the cost of the tires alone keep me from moving up to 19 or 20 inch

Crazy Canuck

The 997 was supposed to be introduced with 18" tires & rims (I would prefer as well).
After most of the development had been completed the MARKETING department requested that 19" wheels be standard equipment on the S. Engineering had to revise the suspension geometry to perform properly with the 19" wheel size.

Note, this is the first increase in overall tire diameter since the introduction of the 911. Rim sizes have increased as sidewalls have decreased.

earlyapex

Porsche went with 19" wheels for appearance reasons.

An 18" wheel is standard on the 997.

http://www.porsche.com/usa/models/91...s/?gtabindex=3

cobalt

Actually the 19" Porsche alloys weigh about the same as the 18" Porsche alloys and only slightly more than the 17" Porsche alloys. So unsprung weight has little to do with it. Also consider tires can vary by weight by as much as 5 pounds from manufacturer to manufacturer for the same size. So it is the total package weight. Add the fact that Porsche is using more aluminum alloys in the suspensions systems vs cast iron of the early cars and you have even less unsprung weight.

Tire sizes of 25" Dia are being manufactured less and less so Porsche moved to a larger dia as did most manufacturers. Run flat tires and other technologies are also changing how manufacturers are approaching what sized alloy to use. Not to mention most people like to see a larger wheel on their cars.

Bob Rouleau

All looks. On a GT3 RS 18 inch wheels clear the brakes just fine and there are more high performance tires in 18 inch sizes than in 19's.

Ray S

+1

cretinx

GRM did a test on plus sizing the wheels

there's really not much of a performance benefit to going large, and once you're in the 19 and 20 inch range its a performance loss (not to mention a huge loss in comfort).

If you're REALLY concerned with some lightweight wheels, I've seen thingies on eBay that change your bolt pattern over to 5x114.3, which will let you run basically all of the tuner wheels out there.

OEM Porsche wheels like the 17" Carrera Cups from the 993 weigh 18/20 for 17x7.5 and 17x9.

I have owned some serious toys (500 whp RX-7, custom turbocharged RX-8, BMW Z4) and I've found that you really CAN go too big with wheels and they have a real noticeable effect on performance in all aspects.

However, I'm not a Porsche engineer - maybe the cars are designed to function around these mammoth wheels - but somehow I doubt it. I would take a look at their straight up racing models (GT3, Cayman S - basically non-poseur vehicles) and see what those cars are rocking.

cobalt

I have weighed the cup II's and my records show the 7.5's at 20.68 and the 9's at 22.3 vs the cup I's which weigh in at 20.46 and 25.96 for the same sizes.

When you compare these to the 8 x 19" factory sport wheels that weigh in at 22.88 and 9.5 x 19" at 26.18 how much does this impact weight considering you are increasing size and width for the added weight and will be using a tire that weighs slightly less than it's 17" equivalent. Suspension components have also gotten lighter from the days when the cup I's were used.

just a thought.

Irksome

Look at Volk TE37s in addition to the other brands listed above. When I was searching, I found nothing lighter for my 996 in 18" (x8.5 and x10).

smshirk

Check out Voxx. they make 18s under 20 lbs with Porsche bolt pattern. I'm not sure about WB offsets, but I know they have NB wheels.