Autocross tire pressue with stock 235/55-17 BFG street tires

[wildswing]

Hey,

I'm driving in my first autocross this weekend and am curious about proper tire pressures. "Expert" advice on the interweb is all over the place. I understand that finding optimum pressures takes time and effort. I get that. I'm not close to that yet. Just want to know where to start. An experienced driver I know is telling me to pump them up to max sidewall pressure. That seems odd to me. I've asked for an explanation. I'm driving the '05 GT. It's got stock size 235/55-17 BFG G-Force T/A tires. Suspension is Eibach pro system plus which lowers the car about 1 1/2" all around. Since this is my first time, I have no intention of beating on the car. I just want to go out and have some fun without hurting the car. FYI, there's no air there and I'll be driving the car there on Michigan's I75 at 70 mph for about 20 minutes. Any advice you may have would be very much appreciated. Thanks in advance.

[Stephen06GT]

I am by no means an expert but have been tracking my 06 GT on various street tires for eight years and this is what I do. A night or two before track day I pump up the tires to 35-36psi. I drive an hour and a half or so to the track. After the first session I check the tires res. Check the tires for signs of rolling over on the edges, and the pressure to make sure it's not too high. Usually it's around 40psi, but if it's higher, I back the pressure down to 40psi hot. After track day, if I remember, I back the pressure down to 32psi and drive home. I will make this statement, I wouldn't recommend pumping them up to the max as the pressure will have "no room to expand" during your lapping session.

Stephen

PS: You are going to have a blast and will be grinning from ear to ear.

[G-ForceJunkie]

You want a stiff tire for autocross to avoid rolling the tire over onto the sidewall. Given your situation I'd probably leave the house with 40psi in them, then monitor and let air out through-out the day when you see anything over 43psi, shooting for the low 40s after a run.

[wildswing]

Thanks guys.

[ZR]

Enjoy yourself, man it's addictive.

[Mellow Yellow]

You want a stiff tire for autocross to avoid rolling the tire over onto the sidewall. Given your situation I'd probably leave the house with 40psi in them, then monitor and let air out through-out the day when you see anything over 43psi, shooting for the low 40s after a run.

This is what I do with my 05 GT.

Will be auto-crossing this Sunday, with the Porsche Club in Chatham.

[wildswing]

Well, that was about as much fun as you can have with your clothes on! It was held at an airport just south of the Soo in Michigan. It's an old abandoned US air force base, so there's miles of very thick, stable, concrete. Here's a link to somebody's GoPro footage running yesterday morning's course.

https://www.youtube.com/watch?v=d8Iauum5g6o

Yesterdays fastest car? A shifter cart. Unbelievable how fast those things are. Next was a bad ass Mustang, which was last year's US national champ, then an awesome mid 60's mailbu with a completely custom chassis and suspension and steamrollers at each corner. First pic is my '05.

https://thumb.ibb.co/n8EaC8/Yooper_Cup2018_1.png (https://ibb.co/n8EaC8) https://thumb.ibb.co/cM26Ko/Yooper_Cup2018_2.png (https://ibb.co/cM26Ko) https://thumb.ibb.co/fxuxQT/Yooper_Cup2018_3.png (https://ibb.co/fxuxQT) https://thumb.ibb.co/nncHQT/Yooper_Cup2018_4.png (https://ibb.co/nncHQT) https://thumb.ibb.co/bWxTX8/Yooper_Cup2018_9.png (https://ibb.co/bWxTX8) https://thumb.ibb.co/fvfhs8/Yooper_Cup2018_10.png (https://ibb.co/fvfhs8) https://thumb.ibb.co/eWp8X8/Yooper_Cup2018_11.png (https://ibb.co/eWp8X8)

[wildswing]

Enjoy yourself, man it's addictive.

That's an understatement! I'm already looking at getting some new rims and tires.

[wildswing]

Here's the location. That pad is almost 50 acres. We used about 1/2 of it and had to srtay off the white areas. GM uses those for winter testing. This AFB used to have B52 bombers.

https://www.google.com.br/maps/@46.250754,-84.4665635,945a,35y,60.72h/data=!3m1!1e3

[wildswing]

For those who autocross, what wheel/tire size are you running. This first time for me was on the stock 235/55-17 BFG G-Force T/A tires. I've been tossing around the idea of new wheels and tires. If they work well for autocross, then even better. I don't think I'm ready for specific wheels/tires just for autocrossing twice a year. I saw a lot of Bridgestone Potenza RE-71R tires on all different kinds of cars. I think those are a little too soft to be daily, or even weekend drivers.

[Stephen06GT]

I was very happy with the Nitto 555 Gen. 1s and hear that the Gen. 2s are even better. For bang for the buck you may also want to look at the Firestone Firehawk Indy 500s.

[Stephen06GT]

Here's the location. That pad is almost 50 acres. We used about 1/2 of it and had to srtay off the white areas. GM uses those for winter testing. This AFB used to have B52 bombers.

https://www.google.com.br/maps/@46.250754,-84.4665635,945a,35y,60.72h/data=!3m1!1e3

Kinross?

[wildswing]

Kinross?

Yes sir. The airport rents what used to be a big staging area to the SCCA clubs to hold the event. They used to use a place out in Brimley, but that's been resurfaced so isn't ready for that kind of abuse again until maybe next year or later. In the mean time they found this spot. It was great. Not a light pole, building, or guard rail in sight. Meanwhile Delta airlines takes off and lands on the runway right beside the pad.