Last weekend I took the 991S out for its first autox. The car has PASM sport, sport chrono, no PDCC, 7MT and stock 20" wheels/pirellis.

Overall I was very impressed with how the car did stock. It is amazing what a huge difference there is in the balance/handling of the 991 vs the 997. You almost can't tell it is a rear engined car. Turn-in on the car is just amazing.

I started at hot pressures close to ~35 front ~40 rear and although the didn't feel awful, thing definitely felt off. We started letting out air and found the best balance/grip at ~28-29 psi front and ~33-34 rear hot. At those pressures the car had little to no understeer and wasn't too loose in the rear either. I wouldn't say the balance is perfect yet, but it was a very good start for a stock car. The car was predictable through faster sweepers and very stable on quick transitions. Roll over on the tires was also very good and tires looked to be in pretty good shape at the end of the day (camber is -1.8 front -2.2 rear).

There have been mixed reviews on the stock pirellis. Overall I found that they had quite a bit of grip, but part way through the 2nd autox lap they were already starting to overheat. The ambient temps were ~60 degrees F, so I was a bit surprised by this. As they started to get too hot, there was progressively more understeer in the front and more oversteer in the rear. I can't imagine using these tires on the track in warm weather. Next event I'll be taking my water sprayer, so I can cool off the tires between runs.

I don't have a mount for my data logger yet, so didn't get any accurate data yet. The PCM gave the following peak G numbers: 1.34 left, 1.29 right, 1.27 braking and 0.93 accel, but I don't really trust them. They seem a bit high for street tires and I suspect are just showing instantaneous peak Gs and not sustained Gs.

The biggest problem with the car on an autox course was the extremely tall gearing. 2nd gear tops out at roughly 78mph and is just too high for most autox courses (and the courses I run are usually pretty high speed). There were several sections where I had to brake or let off just as I was getting into the meat of the power band. If I end up getting a separate set of wheels/tires for autox I will look for the shortest rears I can to lower the effective gearing.

All in all it was a lot of fun. If you haven't taken your car out to the track/autox I'd certainly recommend it. I'll post up data from the next event after I get the logger mounted.

 

nice post! attila are you done with break in already? fine work getting that fine quick fast!

I'm only at 600.miles but I'm going to start to loosen the rpm restriction soon

 

Technically I was only at 1940 miles at the event, but close enough. I was building up the RPMs and load gradually since 1000 miles.

 

my plan too!

 

Thanks for the report. The autox courses I go to tend to have even slower max speed. Can you explain how shorter rears can help? What sizes to consider in order to get in the power band sweet spot, and should the front size match the rear?