NoSubstitute981

I’m not new to autocross but have been out of the game for quite some time.
That said, I’m going from FWD to the following:

2014 Cayman S
Wheels are 19” x 8.5fr and 11” rears
Tires are 245/40 and 285/35 RE71RS
1.3 neg front camber and 1.6 rear with a bit of toe-in

nobody where I’m at are running these tires and I’m having trouble finding the sweet spot.
The sidewalls are so stiff I can’t seem to get a good read on the best (at least starting point) to run with.
All I can say is I ran yesterday with 29front and 28rear hot and spun out twice. Tires are still not rolling over to the triangles.

Best I could find was a thread here stating 32/33 hot but that was on a track car with double the camber.

any help or advice would be greatly appreciated.

edfishjr

-Everyone I know that runs a basically stock Cayman on street tires runs more pressure in the rear than the front....often in the range of 28/32.
-In my experience, very few cars are "bad" if you start with placard pressures if on street tires and basically test up and down from there. Usually 2 to 4 psi lower is best for max grip. Balance is a little trickier.
-I doubt very much that if you started the run at 29/28 that the tire pressures alone were the cause of your spins, or even had much to do with it. There's basically nothing more different than FWD and Mid-engined. When I went from front-engined, RWD to driving several Caymans it was very easy to turn too aggressively and have the front end write a check the rear can't cash and get the rear to slide or even spin. The response is just so much quicker. With 11" rear rim, 285 RE71RS and 1.6 neg camber you should have huge rear lateral capability if not shocked too quickly.

NoSubstitute981

I like your analogy! You are right about that, I definitely have some learning to do! I’m going to try a few things differently next event and try to focus more on being smooth and less on being competitive until I learn this car. I’d just like to get a good starting point with tire pressures so I can turn my focus on driving skill.

Back in the day… we were running Yokohama A008R tires (205/60/14 on FWD VW’’s) IIRC and it was super easy to chalk the edge and go from there. These tires aren’t like that with such a stiff sidewall. They also have quite a rolled edge to them compared to my, what I call, street tires. (P-Zero) They’re basically flat across the contact patch.

I’ll run with higher pressure in the rear for sure by at least 2 psi and see where that gets me. I’m not sure what difference there would be between track and auto cross pressures and grip but thought I’d ask if someone has/had some experience that IS competitive so I can kinda leave that alone for awhile until I get some seat time in.

I think I’m going to leave PSM on for now and shift manually in Sport Plus mode. I have PDK, forgot to mention that… and try to get to know the car better.
I’ve been running in Sport mode with PSM off thus far.

Also, I see guys watering their tires after each run. Is that necessary or just a bunch of BS. The fastest cars don’t do squat!

I’ll take any advice I can get so don’t be afraid to say what’s on your mind.

Thanks much,
Derek

edfishjr

The necessity to water depends greatly on 1) tire type, 2) local conditions and weather, 3) time between runs. What I've learned about the modern tires. YMMV: 1) A052- never let much heat penetrate into the carcass. That means, in hot conditions, you must hit them with water immediately after every run. On really hot days it can be next to impossible to keep them cool enough if you have a co-driver and you can feel them drop off before the end of a long run; 2) RE71RS- handle heat much better than A052. Like to be warm, but not hot. You can over-water them and over-cool them and need a run to rewarm them to restore performance, 3) 660's- definitely like to be very warm to the touch, but have a broad heat range of good performance. If it becomes uncomfortable to hold your hand on the tire surface they need water.

NoSubstitute981

Thanks for that, the guys with the Yoks are mainly what I’m seeing spraying their tires. The majority don’t bother even checking tire pressure. It’s been hot here the last couple events (above/around 90) so I’ll kinda make do with what I’ve got I guess. Pyro meter says around 180ish across the tread the few times I’ve taken temps. We have a long trek to get back to the grid after a run so I figured it’s pretty much a useless measurement.

Like I said, I’d really like to have some pressures to give me a base line on for these tires and just get on with learning how to drive the car.
I did a ride-a-long with a fella that drives a 981 Boxster and is a good 5 to 6 seconds faster than me and I about shiaat myself! His car is pretty much stock also.

sgreer78

re71rs's like to be cool, and 29psi is not why you spun. You have a good baseline.

Abt12

I've been running 31psi hot on my 718 GTS. Our laps are long and fast (.8-.9 miles, 65-70 seconds) so ymmv. 80-85 deg days I've been spraying after the second or third run, basically if I can't keep my hand on the tire I'll spray. I'll spray again after lap 3 and/or 4. Afternoon runs they seem to hold some heat so almost always need a spray after 2nd lap.

NoSubstitute981

Perfect! Thanks for the info. Ours are about the same distance as yours with similar temps too.
I’ll bring a sprayer along as well.

I do understand the tire pressures aren’t what caused me to spin. It’s clearly my driving and I’ve got a lot to learn. I just wanted to take the guessing what pressures to run out of the equation.

Thanks to those that have responded.

Z3papa

That would be too late IMO if you want to extract the optimum run. The RS want to be cool and if the tire is so heat soaked you can't keep you hand on it, the carcass of the tire is so saturated you will likely not get the heat out by spraying. If they are warmer than ambient (ex. 90-100), spraying will suffice but once the tires are 130, a fire hose will cool the surface but not the inside much. In response to the OP, F can vary between 30-32, and R between 29-32 depending on setup.

Abt12

Don't have a pyrometer so can't comment on actual temps, but I've found them very consistent with above method. Lap times decreasing on 2nd and sometimes 3rd lap, pretty consistent beyond that. Lap 5 was a little greasy even after spraying but laps 2-4 were consistent (both in feel and pretty close on times too, accounting for obvious mistakes/areas I tried something that didn't pan out).

nubbster927

2016 Boxster GTS
Wheels are 19” x 8.5" fronts and 10” rears
Tires are 245/35/19 and 275/35/19 RE71RS
1.6 neg front camber and ~2.5 rear
Completely stock, running in A Street for SCCA events.

I've had best success with hot pressures of 33 Front and 30 rear. Seems contrary to what other people seem to like but I've found this gives the rear end a lot of stability and makes the car feel best in my hands and my driving style. I've been winning the last few events in a row with this setup (SCCA, BMW, and PCA autocrosses) so surely it can't be THAT far off. Report back on what you end up liking!

NoSubstitute981

Thanks for that. You must have the PASM or X73 to get that much camber. Best I can get is 1.3 on the front. My plan for the next event is to run with 30/31 and water down after each run. I’ve also got a pyrometer so I’ll be checking temps as well. I noticed I’m wearing the outer edges of the tires more than the inside so I may end up bumping up the pressure a bit from there. I also am planning to install the X73 package over the winter. That should give me a bit more camber in front and I’ll have them dial up the rear a bit as well.

Earlydays

For what it is worth....I ran 32/35 hot on my stock 964 w/ the earlier RE71R

dps214

The outer edges are always going to wear the most until you have 3+ degrees of camber, don't make pressure choices on that alone. We liked 29psi front more than 30-31, I think we ended up at 29/33 on the 245/275 setup. Base suspension, 1* front camber, gt4 rear swaybar. Rear pressure to taste to some extent, on that setup the rear end moves around a bit but isn't remotely unstable or snappy.

Our experience has been that they don't really care about temperature. They're good cold but don't seem to mind being incredibly hot. We've been spraying some mostly just to make sure we don't melt all the rubber off of the outer shoulders.

nubbster927

Whoops I forgot to include that. You're right I have the PASM on my car.