Re: My trick......

What do you guys run your pressure at for autocross? Do you leave it at the recommended 32/37 adjust? I seem to recall Pedro telling me something at BRBS about running the rears at around 40 when doing AX.

Anyone who wants to do some AX tomorrow morning, MSR PCA is doing AX in Millington, TN tomorrow morning. I'll be there bright and early!

... I run 29/40 cold.
I also have 225s (instead of the OEM 205s) up front because I hate understeer.
The lower pressure up front will make the tires grab better reducing understeer.
The higher pressure on the rears dials in some oversteer allowing me to better rotate the car.
It may or may not work for everyone.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Cool, thanks Pedro! I remembered you saying something about running around 40 but I wasn't sure exactly what you said. I was mostly worried about my existing nearly BALD tires at BRBS!

I'll see how they run tomorrow at first and adjust as needed, I'll set the rears a little high before I head out and see how they do.

... have fun.

Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

and wound up with 31F/32R cold - e.g.: +2 F and -4 R. This gave better balance (less understeer) and higher pressures got greasy.

Stock size 205/50 and 255/40-17) Street tires.

Care to comment - or another data point.

Grant

When I autocrossed the '04 550SE, I had best results with 42 up front and 36 rear.....go figure.

Higher pressure up front seemed to help turn in, reducing understeer.

Seems we are all over the place. I did AX a lot with good results.

Track pressures are totally different as turns are not as radical.

THIS IS FOR NONE "R" TIRES.



Edited 1 time(s). Last edit at 08/13/2011 07:21PM by dennisafrompa. (view changes)

In order to obtain the most tires to road contact, I use this little trick. Most tires have a little triangle on the side wall where the tread ends. I purchased some kids outdoor play chalk. Chalk the tires before each run with about an inch plus wide band covering the little triangle and above it on three different places around each tire. After the run, you will see where the tires are making contact with the road. If the chalk is missing at the top of the triangle, you are getting maximum road contact. If there is no chalk showing, you should add some more air. If there is lots of chalk showing above the triangle, you may want to let out some air.

As Perdo was saying, you may want higher pressures on the rears to dial in some oversteer. If so, you want to see some chalk above the triangle after each run.

I usually record the air temp and type of road surface before each event. Also, I record the air pressure in each tire after each run & any adjustments I make.

After a while of doing autoxing you will learn what tire pressures to run based on air temp, road surfaces and your skill level.

Have lot of fun as I do.......

It's bit a while since I auto-X'd but when I did:

I added pressure in the front to prevent roll over and left some out of the rear; I also ended up going either even pressures (f/r) or even a bit more in front--this was on PS2's.

On Victoracers, lower pressures with mostly even f/r.

Given the ranges of the suggestions here, don't be afraid to experiment to see what works best. Chalking the side wall is a good idea.

As a final thought, if you continue with auto-x, consider the Techno-brace that Pedro sells. It seems to solidify the rear in sharp slower speed turns.

Finally, Here's a thread from someone covering his autocrossing experience over several events:

[www.rahul.net]



Edited 1 time(s). Last edit at 08/13/2011 03:22PM by MikenOH. (view changes)

Thanks for the suggestions!
I did an SCCA AX school at the end of May and one of the things they did was chalk the tires. We drove in a tight circle about 4-5 loops around, then stopped to see how the tires were wearing. Mine were set right on the way I had them, which had been the recommended 32/37 cold. That was with the tires I had at the time, and I've since changed. I may take some chalk next time to see how they are doing on the first pass or two through the course and adjust from there. I'd forgotten about doing that, thanks for the reminder!

The AX was a lot of fun, I always have a good time when I'm driving the boxster! Especially a bit more aggressively than I can on the street.

I have not autox'ed or tracked in about 5 years, but with my first Boxster I took my own road (so to speak) for autosporting events. I'm certainly not a professional driver and even with about 15 autox events and 6 track weekends with the club, I am still quite a novice (even though I kept up with the top of the pack). Anyway, I approached these driving activities with the idea of getting to know "my car". Which to me meant driving it with standard/recommended tire pressure on all fours. This may not provide the best timed results in autox (I was often first or second in class anyway), but it provided knowledge and experience about how my car will handle for the 99% of driving that I do - on the road. No, I don't drive on roads like in autox or track, but for those times when you might make an evasive move for safety for in an emergency, knowing how my car would handle was what I was looking for. Bottom line: I used standard settings, the car performed wonderfully, and I felt that I learned a lot about "my car".