I have been running a completely stock 991.2 GT3 on RT660s (265f/315r) so far, fairly successfully. I’m thinking to try more camber, -2.0 front & rear. What do I do with the toe? Bear in mind the car has rear wheel steering.

Also, what is the stock alignment anyway? The camber is -1.3 f/r IIRC.

Another interesting observation is that I like the RT660 at way higher pressures (33f/37r) than my old 997 on 71R (23f/27r).

 

I don't have a car with rear wheel steering, my thought process coming from where you are at would be at least -2.5 camber up front with zero toe. The rear I would use the OEM settings for toe, and -2 would probably be fine for camber.

 

I currently set up my alignment for -2.8 front and -2.4 rear. It helped a lot on turn-in for me. I am relatively new to autocross, as this is my third year doing it. First year with my 991.2 GT3. I also have zero tow in front, with a slight tow-in for the rear. My sway bars are both at middle. I am also interested to hear what others have, both for alignment and their tires.

Like you, I had Falken RT660s on my 997.2 Turbo. 245/35/19 and 315/30/19 and liked them very much. They were so much better than the Michelin PS2 that were on there originally, especially for autocross. The pressures I liked were also lower, 32/33 front and 37 rear. They have a stiffer sidewall.

For the 991.2 GT3 I now have, I am looking to buy 19" Forgeline rims (9X19, 12X19) this week and am very curious what everyone with a 991 GT3 is running for autocross in 19"? My current set-up, on OEM 20 inch rims, are Advan A052 in 245/35/20 and 295/30/20. Once I get the 19 inch rims, should I go back to the Yokos with A052 in 275/35/19 and 295/35/19 (almost the exact same as the OEM wheel diameter, also they are wider in the front, but narrower in the rear)? Or back to my old Falkens, 245/35/19 and 315/30/19 (wider in rear and different diameters and different front to rear ratio than OEM) ? Maybe the CRS V2 in 265/35/19 and 325/30/19 (wider, but .5 inch lower diameter all around, but keep the same front to rear ratio)? Or a mix with Bridgestone 71RS up front 265 or 275/35/19 and Advan A052 295/35/19 for the rear? Anybody have any experience with any of these? For our car tire sizes, thinking only the Yoko A052, Falken RT660, Bridgestone 71RS and CRS V2 are the only "good" autocross 19" tires.

 

So I had this car and found the rear needed more camber than that to be stable in slalom-type elements. 1/8" total toe-in for the rear worked fine.

 

That's not surprising, I have a little more on my rear axle, but he seemed to be wanting to start a little conservative, so I didn't want to argue with him on the rear axle from a standpoint of not actually knowing on that car. The strut front axle seems to like a lot more than -2 though.

 

It’s cool we arrived at the same pressures for the RT660. I wouldn’t mix tire models ever. My understanding of the current relative autocross performance of tires: Yoko > Bridgestone > Nankang > Falken but our sizing sucks for the top 2.

I am not sure what the top cars in nationals SS class are running, most list the tire brand as ‘other’.

 

I too am very interested to hear about which tire sizes for the GT3 the top cars are running. From the SCCA website it looks like the Yokos and Bridgestones are at the top, with Yokos being more at the top.

I have never mixed tires and generally speaking, I think most do not recommend it, however I know one of our local (regional) top performers has 71RS up front and the the A052 in the rear and does quite well.

 

What results have you been looking at? All of this years tour results have actual tire brands listed for nearly everyone, and with one or two exceptions it's all yokohama and bridgestone at the top.

 

https://cdn.connectsites.net/user_fi...pdf?1695755415

Top 3/5 are ‘other’ but you’re right most are mix of Yoko/Bridgestone. @sgreer78 is Bridgestone but it’s a GT4.

Top Nankang is #20, top Falken #37.

 

When I ran SS... I had roughly -2.6 front camber and 0 toe
Rear was set to -2 (did not want to go more than that with the rear steering in place) and I ran a total of 3/16 toe in

Tires we ran the Yoks (255/295 setup) but this was also 3 years ago. Car took the win in SS that year

 

Thanks for relaying your tire sizes for the Yokos. I have been going back and forth on whether to get 275 or 255 up front. The 275 would keep it closer to the front to rear tire ratio as OEM spec. Not sure if the 275 would rub though and be to pinched for the 9” rims.

 

I was the #20 on Nankangs. Last year, I was experiencing a lot of excessive front tire heat saturation with the Stones switched late to the Nankangs to address that issue as I knew SS was running heat 5 in the heat. Watching all my competitors running around spraying the heck out of their tires as I sat in my car with tire blankets was comical. Had it been cool (Wed it was 75 and tires were very sketchy run one with no heat) or worse wet, I would have been completely hosed. IMO -- Nankangs are great dual use tire and are good but not as fast as either the Yoks or Stones. The "other" is because Yom, Bucki and Jay were being coy. I'm pretty sure they were on Stones but didn't commit it to memory but did extend my congrats to all three in impound. I'll be on Yoks this year in AS but seriously considered a mix of 255 Stones/295 Yoks.

 

I was hoping you could tell me what was your front and rear camber? Also, what settings did you use for the anti-sway bars? Thanks.

 

I get -1.4 front -1.9 rear (could get more) and use the rear 718 GT4 sway bar on medium.

 

Thanks for the reply. I didn’t realize that you had a GT4, I thought you had a GT3. I was looking for some solid specs for my car for Autocross.