mopar bob

What is a good starting pressure for RE71r tire on a 911. I couldn't find what folks were saying about that. I remember that pressures are lower so I was thinking about starting at 30/34.

sjfehr

Not really apples:apples, but I run 36F/35R hot on my 987.2S. I tried lower but got more rollover than I was comfortable with in the front.

mopar bob

I ran 36 38 with the RS3's last year so that maybe a better starting point. The RS3's wouldn't let me run lower without getting squirmy with the soft sidewalls. The firmer sidewalls may let me run a little lower pressures and we will see after the first run. Thank you for your input

LexK

What are your wheel width and tire specs? Also, what is the general feeling of the car?

mopar bob

Wheels 8 x 18 and 10 18 and the tires are 255x35x18 and 285x30x18. The car feels more taught on the street than the RS3 tires. I have only put about 50 street miles on them so far at 38 LBS front and 44 LBS in the rear to keep TMPS happy. I'm also installing fresh motor mounts on Friday. After 9 years and 50k+ miles I'm hoping to keep the engine movement down a little with the fresh mounts.

LexK

You have a similar setup to mine in the front where the tires are a little pinched. I run 31-32 PSI in the front (mine are 8.5 with 265 tire). If it wasn't pinched, I would probably run 29. For the rears we have the same specs exactly, but you obviously have a little more weight on them as I am in a Cayman. I run my rears at 28 PSI, so I would say you can come down quite a bit even if TPMS yells at you.

majormojo

Bob, I have the same wheel sizes and ran those same tires last season, albeit in an '11 Cayman S. After some experimentation, I settled on ~ 35F/33R hot. Starting pressures cold 33/31. That's on an extremely grippy rough asphalt surface. On smoother asphalt (or in the rain) I'd aim for 33/31 hot. This year I'm running 265F/285R so I will be experimenting a bit again at the start of the season (this weekend!).

mopar bob

I don't worry about the TMPS when I run I just like to keep all warning lights off on the street. PPIR has older asphalt that is not flat but is quite bumpy.

jbrennen

Not sure how much of this Cayman data applies to a 911, but I'll throw it out there for what it's worth...

Yesterday I had a chance to autocross two very similar cars with RE-71R tires and I paid attention to the tire pressures on both of them.

My car: 981 Cayman GTS, X73, PDK, PTV, 4th autox on the tires.
Other car: 981 Cayman S, PASM, PDK, no PTV, 2nd autox on the tires.

Both cars have maxed out front negative camber as far as the stock hardware allows.

In my car, I've been aiming for a hot pressure of about 30-31 PSI at all four corners.

Data points:

My car: Lap time of 1:17.62 in practice with hot tires at about 31 PSI.
Other car: Lap time in practice of 1:17.70 with hot tires at about 33 PSI.
My car: First timed run of 1:17.51 on cold tires at about 29 PSI.


After I ran the 1:17.70 in the other car, I decided to bump my starting PSI up for timed runs, and was going to aim for 32 PSI hot.

My 1:17.51 on cold tires was good enough for third top time of the day among about 100 entrants, and I wasn't able to better it as the tires warmed up.

I'm not sure there's enough data points here to make any solid conclusions, but it could be that the optimal pressure for a PASM-equipped car is higher than the optimal pressure for an X73-equipped car. That would make some sense, because the X73 really cuts down on body roll and thus on dynamic camber changes. I could feel the body roll on the PASM car was much more noticeable that my own car.

However, I think the main thing I would encourage would be to experiment with lower pressures. The sidewall on the RE-71R is very stiff.

mopar bob

I ran yesterday but my results can't be used as I was in heat 1 and it was 46 out. By heat 3 we were in T shirts luck of the draw. We started at 32F 35R plus I was the first car out for the season. Being that cold it's hard to tell but the car felt good. Rollover on the front looks good but the back may need to go down a pound or 2.
Alignment on my car is max neg. camber in the front 0 toe -2 deg. camber and -.12 toe in the rear. The car feels better than it ever has.

burglar

You'll really like them when you get a few events on them, they get faster pretty quick and stay fast until they cord.

sjfehr

RE-71R will heat cycle out with enough runs; depends on the circumstances whether that happens before or after they cord.

BHunt 72T

We have an old 911T (2400 lbs) and are thinking of running the RE-71's (205/50/16) occasionally for Auto-X and track days. We typically run a couple of more PSI's in the rear... any advice on optimal hot temps would be helpful... Thanks!

sjfehr

A Bridgestone engineer said optimal temperatures for RE-71R are 120-130F and safe to run up to 160F.

Anecdotally, I've found high levels of grip anywhere from about 90F-180F but found spraying helps keep them from overheating and minimizes heat cycling. The symptoms of overheating are similar to those of heat cycling out: they lose combination (lat+long) grip on corner entry and corner exit and give surprise understeer/oversteer in conditions they had always held in the past.

knfeparty

Found 31-32 front has been the sweet spot with the 996, however with a fresh set on concrete, I wasn't getting any rollover and ran them lower at 29.

For the rears, I ran the 285 RE71rs at lower pressures than the 315 Rival S (10" wide 18" diameter wheel). I got as low as 35-36 and they still behaved well on concrete.