[Tim202]

Has anyone autocrossed enough on the stock tires to know what tire pressures to run?

[MatthewAMEL]

On a cool day on sticky concrete, I ran stock (32/32). Kept them there between runs.

Last weekend it was 80 (same surface) and I went with 32/30.

The rollover indicators on these tires made me laugh. Most are little pointers. These are little Goodyear emblems.

[Egon]

The general reason that people overinflate tires at autocross is to prevent rolling over the sidewall during hard cornering. One way to check to see if they are rolling over is to use chalk. Start your runs with the tire at stock cold inflation pressure. Draw chalk lines as if they were radiating out from the center of the tire to the tread shoulder. After you complete your run check the chalk marks to see if they have been rubbed off or smeared past the shoulder on the sidewalls. If they have you will need to add air over the stock inflation pressure to counteract that. Keep in mind that due to the heat from the run the pressure in the tire will have already increased and it may not be necessary to add more, just redraw your lines and check again.

Keep in mind this will just be useful to check for shoulder roll over, but it will get you in the ballpark. Tire pressures are a great way to help fine tune a cars handling, but they will differ from day to day, racing surface to racing surface and driver to driver. What works for one person may not work for you. I would suggest experimenting, starting with the chalk test and see if your times improve. If you are looking to get every extra ounce of performance out of the car you will need a tire pyrometer to measure temperature differences across the tire. Don't get one of those infra red non contact ones either, get a real probe type pyrometer and learn how to read your tires. Or you could ask around to see if someone in the San Diego region who already has one and would be willing to read your tires for you. (ask nicely!) I used to see the units laying around in the pit area during test and tunes when I ran at Qualcomm and I believe people brought them for others to use, I just didn't know what they were for back then.

[SS 1LE]

Originally Posted by Egon

The general reason that people overinflate tires at autocross is to prevent rolling over the sidewall during hard cornering. One way to check to see if they are rolling over is to use chalk. Start your runs with the tire at stock cold inflation pressure. Draw chalk lines as if they were radiating out from the center of the tire to the tread shoulder. After you complete your run check the chalk marks to see if they have been rubbed off or smeared past the shoulder on the sidewalls. If they have you will need to add air over the stock inflation pressure to counteract that. Keep in mind that due to the heat from the run the pressure in the tire will have already increased and it may not be necessary to add more, just redraw your lines and check again.

Keep in mind this will just be useful to check for shoulder roll over, but it will get you in the ballpark. Tire pressures are a great way to help fine tune a cars handling, but they will differ from day to day, racing surface to racing surface and driver to driver. What works for one person may not work for you. I would suggest experimenting, starting with the chalk test and see if your times improve. If you are looking to get every extra ounce of performance out of the car you will need a tire pyrometer to measure temperature differences across the tire. Don't get one of those infra red non contact ones either, get a real probe type pyrometer and learn how to read your tires. Or you could ask around to see if someone in the San Diego region who already has one and would be willing to read your tires for you. (ask nicely!) I used to see the units laying around in the pit area during test and tunes when I ran at Qualcomm and I believe people brought them for others to use, I just didn't know what they were for back then.

I was actually reading a few autocross blogs recently, and they all seem to say one of the most common set up mistakes is too much psi in the tires...

[DFW1LE]

I would think the stock tires on the 1LE have such stiff sidewalls that rollover would be unlikely??

[Egon]

Originally Posted by SS 1LE

I was actually reading a few autocross blogs recently, and they all seem to say one of the most common set up mistakes is too much psi in the tires...

Yep that's why I talked about using a pyrometer to read the tires correctly. I would really be surprised if there were any rollover on the Goodyear 3's even at stock pressure. It used to be necessary to overinflate due to rollover because tire construction was behind the curve. Modern tires especially those made for autocross/track like the Goodyear 3's, Hankook RS3/RS4, Bridgestone RE-71r all have stiff sidewalls and probably don't need any extra help in that department. Setting different pressures on the front and back can help tune out any tendency to understeer/oversteer though.

[tx6g1le]

I had no rollover issues last week on 36 psi.

[MatthewAMEL]

Originally Posted by tx6g1le

I had no rollover issues last week on 36 psi.

36 is a tad high.

Remember, the point is to get the pressure as low as you can. Right up to that moment of sidewall rollover. Gives the tire more opportunity to flex and keep the contact patch firmly in contact with the surface.

Most FWD folks have to air-up their tires because the front wheels are doing all the work. In my Focus, I always aired the fronts up and the rears down.

The G3 has a fairly stiff sidewall.

[Eric SS]

Originally Posted by tx6g1le

I had no rollover issues last week on 36 psi.

That seems pretty high.

[BigEnos]

I believe that the anti-rollover effect more air has vs. reasonable air on most tires is negligible. It's the carcass and sidewall design that has the most influence on that, and adding a ton of air isn't going to help that much. I agree that the objective is to run as little as you can get away with, but a little more air can help turn-in and you also can get some really bad wear characteristics at ultra-low pressures. I always drop my pressures quite a bit on low-grip (rain, sealed asphalt, etc).

[whiteboyblues2001]

I ran 35psi at the HPDE I went to, BUT that was hot pressure measured right after I got off a track session. Seemed to work well based off of shoulder wear, but overall wear seems to tell me to use a little more pressure. I'm no expert on how to extract the most performance, just looking at wear as an overall indicator.

Just to be clear, I have a regular SS, NOT the 1LE (which has different tires, IIRC).

[WhyUMad1LE]

The performance supplement says 35/35 for track driving

[Eric SS]

Originally Posted by WhyUMad1LE

The performance supplement says 35/35 for track driving

I don't have the manual in front of me. Is that starting pressure or what to shoot for? I don't think I would start at 35psi especially for HPDE.

[WhyUMad1LE]

Corrected