Track tire Pressure

[Swank911]

I am running BFG R1s, original design, on my 911 for autocross.

I run fairly low pressure to make the stick and use the extra stiff side wall to my advantage.

I am now going to my first Driver's Ed event. I have been told that tire pressure is needed to sustain the high side wall load encountered in the corners.

Does any one have an idea of what I should start my pressures at? I will make adjustments as I drive, but I do not know where to start.

Thanks

[Swank911]

help

[Jack Olsen]

In my experience, it's good to start with 31F/33R. After your first session, jump out of the car and check pressures. If they're in the 38-40 range, you're pretty good. If higher, bleed them down to about 38. You want them peaking at about 40psi on the track, but by the time you're checking pressures it's going to have come down a little.

Check periodically during the day. As the track gets progressively hotter, and the heat soaks through all the metal parts of your car, you may need to bleed more off.

These are very general recommendations. Different tires do better at different pressures. Tou can chalk them to monitor your contact patch, or check temps across the surface of each tire with a contact pyrometer to fine tune things. But for your first DE day, even with autocross experience, I don't think you're going to need to get into those kind of details.

EDIT: I'm not familiar with the BFG's. I just did a search, and some guys keep these particular tires at no higher than 34-35 psi, sort of like Yoko A032R's. Hopefully someone who's used them will chime in, here.

[Randy W]

The original R1s were unlike any other R compound tire and still are. They act more like cantiliever slicks with their extra stiff sidewalls. I used these for a couple of years autocrossing before they changed to the new "improved" design. They worked best when the pressures were 23 front and 26 rear when hot. Alot of the track guys started them at 20/22 cold!

[TimT]

I have heard 1lb air pressure per 100lbs of car weight. The amount of pressure used varies with the weight of your car. It helps to know the actual weight (corner) distribution of your car. The chalk test and taking tire temps will tell if your in the ballpark

[Swank911]

I run 24F and 39R for autocross, this is the best I have found for my driving style.

The chalk test. I have seen it on tires but am unsure of the correct placement of the chalk. Should it wrap the shoulders of the tire or be only on the side wall?

[Randy W]

The original R1s have a pretty square shoulder. I'm not sure white shoe polish as usually applied to wrap around the shoulder onto the sidewall will tell you what you are trying to determine - appropriate tire pressure. If you can, borrow a pyrometer and measure temps across the tread to see if you are running too high a pressure in the rear (pyro temps higher in the middle tread).

[Swank911]

As this is my first, I just do not want to run to low a pressure and end up in trouble.

But I will surely be playing with the pressures as I return to the track.