What do you guys recommend tire pressure wise for an auto-x event running on stock Pirelli 235/55/17 tires?

 

Further to the OP as Auto X runs are so short do you set them at the desired pressure right from the start, i.e. don't worry about them increasing as they warm up as at a lapping event?

 

Start out with 2-3 psi over stock.

Get a piece of chalk and draw radial lines at intervals around your tire. After each run take a look at the chalk marks - if quite a bit has been rubbed out from the tire bending over on its sidewall, run some more psi, and then repeat after each round. Make sure you pay attention to how different pressures affect the handling. Eventually, you'll find a sweet spot.

PS. Make sure you keep the pressures within reason.

 

first response. Don't,lol. I've never been a real fan on the stock Pirelli's, but when it comes down to it, you do what you gotta do to have fun.

Now, to elaborate on munchies, look on your tire for some arrows along the edge of the tread pattern. typically there are three or four per tire pointing outward from the rim. make a chalk line next to the arrow from the tread toward the rim. The chalk should wear to the point of the arrow. If your line outward from the point, deflate a little, if it's too far inward, inflate the tire.

On my 18's with my stock goodriches I've found 35psi to be a good starting place for me.

 

The pressure that you are interested in is the hot pressure, because that is the pressure that the tire is actually operating at and what your "feel" and feedback is based on. It´s probably easiest to set the pressures when you first get to the lot before you do anything else.Just driving there will put your tires closer to "hot" conditions. Plan on bleeding a little off after each run; it´s easier than adding some, and you probably will see a slight increase over the first couple of runs.

I would run a little more front tire pressure than rear, maybe 3 or 4 psi. A little more up front makes turn-in response a little better, and a little less in the back can reduce the understeer a little while allowing for a little more forward grip on corner exit.

Right now, I´m running 33-ish front, 29-ish rear in my 18" BFG´s for daily use, and the scuffing goes about to where the little arrows/triangles would be if the tires had them. That includes some pretty hard cornering, though not quite auto-X hard. For that I´d start about 4 psi higher.


Norm

 

+1 on the pressure split from front to rear. A scraggly old guy tipped me off to this on my first HSDE, and it helped quite a bit to balance the car out (I was on OEM tires at the time).

I've tried even wider splits (8-10 psi difference) with mixed results. The BFG's seemed to like it, but my Yoko's are not so happy. I'll be sticking to within a 5 psi difference at my next event.

Best,
-j

 

Take this FWIW since I don't often run on stock tires....

I messed around in my '07 one day when I designed a local event course. I didn't add any air at all (32 all around), and had 3 big guys in the car. The tires never rolled off onto the sidewall. That is a rarity with what are considered to be nothing special street tires. What is tells me is the carcass of the tire is quite stiff, and I don't think the Pirelli's necessarily need a lot of air.

Please bear in mind my car is otherwise setiup for FS, and becaue of that had -2.1 camber which certainly didn't hurt the way the tires reacted. The car was certainly vauge, but all the extra weight and the fact I wasn't on Hoosier A6's probably had a *little* something to do with that feeling.

I agree on a split in most cases. Tires have spring rate, the more air, the more spring rate. However, there are times you can use more air in the rear than you might need to otherwise support the load to add spring rate to the tire and help rotation. That said, it goes more for the sticky tires, as balancing the car on not-sticky tires isn't hard to do with the throttle.

The key is maximum grip. To get it, you need the maximum contact patch. And that means air pressures might vary, and due to tire construction will.

In the end, your pressures might be way different from someone else's with a similar size tire. Could be different tires, different suspension parts, different alignment.... and on and on. Bottom line is if you are really tearing up shoulders, you could probably use more air.

Best I can tell you, based on my car it that I'd start around what Norm was running... say 35/32 (or some sort of similar split) and see what happens. And I'd remind you that autox is a driver game, and if you overdrive the nose, or are running on lots with a lot of hard off camber stuff both those things will tear up front tires even if the air is "right".

 

I managed to loose my autocross log book, including my tire pressures...what do you run on your A6's? I finally got a pyrometer, but need a decent place to start. I'm on Hankook 270/40/17, C70 compound, with -1.5 of camber...and it seems I converged on 35/33psi last year, but I sure can't remember now.
Thanks!
Jim