ChrisF

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Carrera GT

Hopefully OZ Racing, HRE and Forgeline are ahead of the curve and already have a 991 GT3 wheel (front and rear) ordered as a spare part; if they build a 19, that gives us access to Hoosiers.

Paradoxically, the PCCBs will be too big to fit inside 19's. Those wheel makers need to design a one-piece wheel with a recessed barrel to clear that freight train of a caliper on the 991.

Maybe the 19's will even have trouble clear the rear steer hardware, which would explain why Porsche went to 20's. There's no other explanation on the planet for going to 20's.

Does anyone happen to already know the offsets of the GT3 wheels?

Suzy991

They went to 20" on the Carrera from a design point of view. Simple explanation: The car got bigger and the bigger wheels make the car appear smaller. I've read in an interview in some German carmagazine a while ago that going to 20" on the Carrera S gave them the oppertunity to go for bigger brakes on the GT3. They cannot fit smaller wheels to their sporty topmodel... That would be weird from a marketing point of view. If it was a racecar, it wouldn't mind, but it's still a streetcar. Don't think the GT3 Cup will have 20"

I have the German GT3 catalogue here and this is what it says about the wheels:
Front Axle: 9 J x 20 ET 55
Rear Axle: 12 J x 20 ET 47

Here's a link: http://files3.porsche.com/filestore....8-478a67ac9487

Suzy991

10 GT3

Just going from the 19" wheels on the 997.2 GT3 to the 20" wheels on the 991 GT3 increases the cost per rear tire goes from $620 to $900 a tire. I would hate to think if they made a 21" track tire how much it would cost. Could they instead offer 19" or 18" wheels instead?

Carrera GT

It will need Hoosiers. Hence 19's. But 410mm PCCBs under 19s?
PCCB calipers with spacers or specific wheel carrier?
So I think it's going to be PFCs or Movits with the stock red calipers.

Carrera GT

Thanks!
I should have looked for the English version of that document.
410mm 390mm PCCBs has me wondering if Porsche has different wheel carriers or just offset spacers for the calipers.
I assume the calipers are fixed bridge and will have the same issue of needing to be studs or at least TIME SERT to endure repeated pad swaps.

I don't accept this explanation (rationalization) at all. If anything, going to 20's cost the car in terms of tire development and unsprung weight. The new forged 20 was surely a necessary "hit" in cost of materials, just to keep the weight down because a cast 20 would be so heavy as to have discernible impact on the contact and adhesion of the tire. Porsche argues this happens when going from steel to ceramic, so I doubt they'd argue going to 20's was no big deal for unsprung weight criteria. If anything, I'm starting to see 19's, a simply ridiculously oversized wheel, to now be actually the "sweet spot" of overall wheel and tire packaging. Big enough for monster rotors, usefully smooth in term of the rolling characteristics of the tire, yet readily packaged in the 991 and 997 and with available Hoosier and road tire selection.
I think it was unimportant to put 18's on the 997.2, but I think its really going to be mandatory to "downsize" to 19's on the 991, at least until there's Hoosiers or something for the track.

Petevb

We'll need to see the dimensions of the calipers, but it's probably doable with the right wheel. I'm running 17" wheels over 350mm PCCBs; 19s over 410s would nominally have 4.5mm less clearance, but it'll all come down to the specific wheel and the caliper design.
Seems just a matter of time before hoosier does develop something.
For what it's worth, I've got Dunlop Sport Maxx Race tires on 19s at the moment, and honestly the tire sidewalls are so soft it feels like they need 20s.

I don't think looks are solely driving the larger wheel diameters. Instead I think it's a combination of ride and performance. A larger tire OD will improve both ride and grip (mostly braking/ acceleration?). Softer sidewalls also help ride, but then the only way to keep transient response reasonable is to increase wheel diameter. They've been playing this game for two decades, and as tires evolve it seems they have a way to go. However you need tires designed for these bigger rims to make it work, and vice-versa. Hence the Dunlops not feeling too hot in transient response on smaller rims, at least in my experience.

wanna911

I disagree. I don't think a legitimate argument can be made for any performance gain being had from 20" wheels. Any gain in contact patch (which only really happens when you increase OD & Width together), will be negated by the weight gain and unsprung rotational mass cause by heavier wheels and heavier tires to boot. Acceleration will be hampered by heavier wheel/tire combo's just like the handling.

As for ride quality, bigger wheels ride better on smooth surfaces, but all of that goes out of the window on anything bumpy. Especially at speed. I have tracked 20's and street driven them.

The change is all about the bling. Big bling brakes need big bling wheels. Wheel well gaps filled with wheel, no space, and no big rubber. Looks a lot better, performance, not so much.

Petevb

Do you think that 18s are a performance advantage over 16s? Don't all of the same issues you mention above also apply?

This is the same debate that's been going on since the 959 got "ridiculous" 17" wheels. Changing tire technology, heavier cars, etc move the bar...
Bigger wheels do ride better if you hold tire sidewall height constant. Which is what you need to do if you want to keep transient response time constant.

Conekilr

The standard GT3 brakes calipers are 380mm, the same as the Cup cars and they are running on 18" wheels. Recognizing that the caliper dimensions may be slightly different between the two, I would hope that a 19" wheel can be made to work on the GT3 for track wheels...

TRAKCAR

Maybe the 991 Gt3's still will have to point by the olds relics due to the lack of available R compound and sicks!

CUP has 18" if its good for a CUP it's good for an identical GT3 with interior, it's what makes Gt3's so great..

Oh, wait... Crap.

Conekilr

The calipers on the Cup car looks alot more tapered than the GT3's, so I'm unsure if an 18" wheel will fit. I certainly hope so though...

TRAKCAR

Porsche should offer 18" optional.
Certainly would add to track credibility, but they have seemed to have abandoned that thought.....

Petevb

I think Hoosier and other tire manufactures react to Porsche and other car manufacturers. Not the other way around.

I might argue that Porsche should work with Michelin/ Pirelli/ BFG to develop an R1 / A6 style dedicated track tire for the GT-3/ RS. I'm sure they think the market (mainly north america) is relatively small to justify this, but that would restore lots of track cred while offering a better package.

TRAKCAR

you again with your smart logical explanations
But for now, today long before the car arrives I can worry about tires ;-)