SamFromTX

I thought it was a regulation for Cup cars, no? Hoosiers are street tires, the DOT said so

Mass_K

Sure... the volume is not totally constant, but it will not keep increasing as the pressure increases. It gets to a point where the tire won't flex anymore, which is theoretically (at that point) a constant volume. Thus with the increase in pressure the temperature of the air will increase within the tire. Due to temperature equilibrium, the air will transfer its heat energy into the tire, ultimately increasing the temperature of the tire.

If I'm wrong I'm wrong, but that is my opinion on the matter. I guess you could take into consideration the fact that the rubber will flex less creating less heat in the tire, but from a technical point of view, i.e gas laws, the temperature of the tire will be greater with increased pressure.

Keith Verges - Dallas

I thought Porsche had discretion to equip its Cup cars as it sees fit. Now it may be constrained by regulations for other series in which variants of the same car compete, but I've personally never seen a race oriented car with bigger than 19" wheels on it. For example, the P1 GTR, which really does not need to be homologated to any standard, has 19" wheels on it, despite the P1 having bigger wheels. That speaks volumes to me and as practical matter if I do want to run slick tires or have a wider choice for DOT rubber, I prefer 17-19" wheels. Or smaller (one of the many things I love about my SR8 is the 15/16" wheels and vastly less expensive tires than my big street cars). The Raddy could easily use 17" wheels with different tires to have same overall diameter, but does not. I don't see that as any kind of performance oversight.

Bigger diameter wheels became popular because many race cars implemented them to clear bigger brakes. It's gotten out of control as a fashion statement with 20"+ wheels, IMO. I don't see why anyone would run a wheel bigger in diameter than necessary to clear brakes. I've heard the "contact patch" argument, but the contact patch should not have much, if anything to do with wheel diameter - at most the OD of the tire will affect that and I suspect more sidewall can actually increase contact patch due to ability of the tire to deform a bit more. So if you want more diameter of teh overall wheel and tire assembly, just go with a taller section. And a bigger dia wheel and tire is heavier, increasing unsprung mass. Not only heavier, but also with a bigger moment of inertia due to concentrating all that mass near the outside diameter. There is probably no way to test this, but I just don't think the 21" rear wheel is, in and of itself, a performance advantage on the RS. It would be interesting to mount a 20" or smaller wheel and do instrumented testing, but I don't see anyone doing that.

I have gone -1 or -2 in cars where I can clear brakes in order to get weight down, increase tire choices, and reduce consumable costs. And I've read tests with this approach and seen lower times, at least on lower power cars.

Nick Yoskin

any update on 20" R7?

CMS

First sizes are scheduled to be 315/25/20 and 325/20/20. 245, 265, and 295 will follow. Currently scheduled for fall release.

Nick Yoskin

Thanks!

allans

Talk about low profile ....

TrackFocused

Great news. Thanks guys

Joe731

Any sense of rolling diameter of these first 20" sizes? 315/25/20 and 325/20/20?

And more to the point, will any pair with a 265/35/19 R7 to maintain the rolling ratios of the RS?

Stock Fronts are MPSC2s at 265/35/20 = 27.3" Diameter
Stock Rears are MPSC2s at 425/30/21 = 28.7" Diameter
Difference in front/rear diameter has rears being 5.1% larger

A R7 265/35/19 Diameter is 26.2 (they make this today and it would fit the front), so in a rear we would be looking for something close to a 27.5"

CMS

We have repeatedly expressed our preferred 20" tire sizes and concern to Hoosier Race Tire regarding the sidewall profile, rolling diameter and corresponding load rating of their 20" proposed sizes. At this point we don't have any specific diameter measurements but are skeptical that they will work for the 981/991. Hopefully we are wrong. Only time will tell though. As soon as we see the first 20" tires we will report back with measurements and thoughts on fitments.
Thank you.

Joe731

Reviving an old thread re Hoosier R7's in 20"

Any new Intel? Anyone have a good contact at Hoosier?

qbix

No 305/30 ZR20? What are you gonna put on the rears?

Joe731

The idea would be that if Hoosier produced a 345/30/20, we GT3RS guys could downsize 1" in both the front and rear from 20/21 to 19/20 and more easily keep the rolling ratios that keep the nannies happy.

Problem is that the rumor of a 20" R7 has been circulating for 2 years now and still no tire.

TRAKCAR

I ran low profile R6 on the racecar and blew two tires, once hitting a concrete wall pretty hard.
Be careful....

IvanBurns

I just got an update on the status of 20" R7 Hoosiers from the company's Circuit Racing Product Manager. Progress looks promising. Here's what he said:
This is good news for 991 GT3 owners. They certainly nailed the initial sizes for us! I have never wanted to downsize to 19" wheels, and I'm really looking forward to these 20" R7s!