orthojoe

Can someone explain to me why the pressure settings for the GT2RS are much higher than the GT3? They weigh about the same.
Door pressures are 29/33 on GT3 and GT3RS but GT2 is 35/39. Pretty substantial. My buddy drove his RS at Sonoma last weekend and confirmed the car needs high pressure. When he bled out air performance would drop. He ended up running 36/39 hot in the end

Kobalt

I guess: the high GT2RS pressure is when doing 310kph+

Kobalt

In my car there where two pressure alternatives. One normal and one rather high.

Kobalt

Ohh forgot to add: the R-tyre comes with another pressure for the GT2RS (than the normal tires.).

race7117

I think there is a like a 100 lb difference between the 2rs and the 3 mostly in the engine weight, possibly water weight in the frunk? Not sure why tthe diff just throwing out ideas

Kobalt

orthojoe

^now that is interesting.....

A/S

It makes absolute sense. It saves Porsche and Michelin from having to build a tire specific to the GT2RS that can run 29f/33r and still pass 205+ mph. You can increase the load rating of any tire by adding air (up to a limit of maximum pressure and/or construction).

Most super-performance tires cannot handle speeds over 200mph, just read articles on what Bugatti/Michelin had to endure to have a tire that could support the high speed loads from the Veyron.

The very popular track day Bridgestone RE-71R street tire is only rated at 168mph. I have told a few drivers at Daytona (DE drivers) to run something else. It is not only that cars with 450+ hp can reach 168mph there, but the right side tires get heavier loads than running on a flat surface, so at any speeds over 155mph on the Daytona banking, a W-rated tire can fail.

One thing I like about the GT3RS rear tires (starting with the 991 series) is the massive load rating (2200#), Daytona safe!

cbrett

on this topic....anyone have any recs for what they have been running for pressures on their new 3RS?

signes

Static weights are the same but at speed downforce of 2RS quite different, as are top speeds. All of it requires high pressures.

What Kobalt posted above is like my E63 wagon. Two different ratings, one for higher loads and higher speeds. Increase as I recall is 5-6psi increase for each axle.

BK77

Yes, they are a little higher on the 2RS. I ran Sebring this weekend and found that 34/38 hot was the sweet spot.

milaadf

could be because of the extra torque of the turbo motor may require more tire pressure to keep the sidewall from deforming.

skippyBKR

Just to add to this mystery - I have a fellow competitor in Tarmac Racing who races a 800hp Mustang with our 305 MPSC N1 and he also runs 40 psi on this tyre (hot). My experience was that the MPSC drops off like crazy over 36 psi. I still don’t understand this. The Mustang is obviously a lot heavier - but how does it not chew it to pieces?

Raucky

I ran mid-ohio this past weekend and my front 265/35-19 Hoosier started to delaminate when I ran at 32-34psi hot. I ran the exact setup on my gt3 991.1 without any issues for two years. One weekend and the front is toasted on my gt2rs. Couple people told me more psi (40-44 hot)......each psi is worth ~28 lbs of effective spring rate. I guess a higher performance car, 3535lbs with driver needs more “spring” ???? Next track outing is a ways out to test this but, I will for sure.

Dougr743

It could be many things.
1. torque curves are higher, and start lower in the RPM curve, lower initial speeds when the curve comes on.
2. spring rate (my best guess, and #1 guess), i don't think its torque, but could be a part of the tire fatigue
3. something special with the tire compound, but thought they are same as rs?
4. camber caster toe setup? Maybe its different to manage the output, kinda like setting up a drag car, increase torque and HP and you have to really start changing the set up on the chassis