Autocross tire pressures

[Blackcloud]

Any autocrossers out there with a recommendation on tire pressures to run? I have a base Boxster with 16 inch wheels.

[thstone]

What tires are you using?

[Blackcloud]

Formoza f-1 on the front. Rears are a different make, I'll check when I get home tonight...can't recall the name!

[Topless]

Yes exact tire sizes and model please for best response. Also your skill level: How many years have you been AXing? Any suspension changes or stock?

I was not aware you could still get 16" wheels on a 2004 Boxster. Hmmmm.

[Flavor 987S]

Originally Posted by Blackcloud

Formoza f-1 on the front. Rears are a different make, I'll check when I get home tonight...can't recall the name!

You need 4 matching tires. Then worry about proper pressures.

[jb92563]

With different tire makes and supposedly different stickiness of the rubber it will probably be a bit difficult to predict how the pressure needs to be adjusted.


I'll give it a shot at explaining and then the experienced racers can correct and fill in the gaps. (I'm still very new to AX, under 10 racing days)


It may be a case of trial an error, but from what I recall was told to me at an AX you start with the tires recommended pressure and then + or - a pound or two of pressure at a time depending on what the tires/car do when cornering hard.

The goal is max tire contact with the pavement and equalizing the front and back adhesion so that you have the best grip possible and equal break away of the front and back under higher G's. To reduce under and over steer.

[The Radium King]

36 front / 38 rear work for me.

[Bigsmoothlee]

I liked 34/38 on street tires.

On slicks I like 35/38

[Bigsmoothlee]

Just use shoe polish on the sidewalls, go for a run, and see how far down the sidewall the polish wears ( most sport tires have a little arrow at the top of the sidewall ).

Add/remove pressure until you find your sweet spot.

As you get used to the car, now you can go up or down from there depending on your driving style and the tires reaction.

[Brad Roberts]

I run our Hoosiers at 24 cold.. lol for 30hot (on most SoCal days) Maybe 32 if we are playing with chassis tuning.

[Bigsmoothlee]

24 seems really low. I tried running kunmho v710s at 30 psi and ended up losing pressure through the sidewall after a run...

[Brad Roberts]

Big,

it depends on the tire size and whether it is an A6 or an R6 It also depends on surface and surface temp.

cant say that I've lost pressure through the sidewall on ANY tire, but I *guess* it's possible??

[j.fro]

A bit off the OP's specs, but on my car I run 32front/34 rear. Hoosier A6, 2700# car, -3.4 camber front, -3.2 camber rear.

[Brad Roberts]

Whats size tire??

[Brad Roberts]

When people say *run* "J.Fro" is that cold or hot?

[j.fro]

Ahhhh...
I start 1st run at those pressures, reset to those after first sand second runs, then possibly adjust in later runs. On a typical 90 degree day, I gain 2 psi all around on he first run, about the same on the second, 1 psi for the third. Then it's usually time to break out the sprayer to cool the tires, and things stabilize.
Brad, just to give a bit of info, Kenny Schreeves and I set the alignment two years ago. Last year I took a PCA regional AX championship, NASA Mid-Atlantic class and overall champs, and SCCA regional F-Prepared champs. The setup seems to be working really well!

[Brad Roberts]

I forgot your name, but I recall the conversation!!

You see me pointing people in your area to him

I support and send customers to shop owners nationwide.

[tnoice]

I have 18's and the RE11s. I run 34 in the rear and 32 in the front.