I wanted to see what tire pressure some of you run at the track.

 

I was at a track for the first time on Tuesday. They told us to inflate our tires, cold, to 5-10 psi above street specs, to help eliminate having chunks taken out of your tire. I ran the rear tires at 42 (vs 32) and the fronts 38 (vs 32).

 

how did that effect the grip of the tires and the handling of the car?

 

Beats me since it was my first time on a track. Certainly, I had no problem with handling, except when almost airborne at one particularly interesting spot (cresting a hill, at 95mph, into a significant braking point). I doubt that somewhat over-inflated tires would help there, however!

 

Tire pressures (and camber settings) are very tire and car specific. Essentially, you want to have a high enough pressure so that the tire contact patch is stable while cornering. Basically, not deforming the sidewall and losing grip and possibly having the tire come off the wheel. You don't want the pressure too high as it will make the tire "rounder" and reduce the size of the contact patch, i.e. less grip.

Most street tires have a relatively soft sidewall, so require higher pressures to keep the tire stable in turns. Racing tires tend to have relatively stiff sidewalls, so don't need high pressures. Some extreme examples. I have a Integra with tall 60 aspect ratio all-season tires. To prevent the sidewalls from rolling over (in autocross) the pressures had to be increased over normal to 40psi (+11). The S2000 has Toyo RA1 competition tires. On the track I currently drop the pressure to 26psi cold (-6), and have no sidewall rollover issues. The recommend cold pressures from Toyo are actually a lot lower at a 18psi minimum!

It is basically trial and error, unless you can find someone with the exact same setup and driving style as you. Start off with the recommended "competiton" starting cold pressure, or for street tires add some pressure. Do a quick session to get the tires to operating temperature. Note how the car handles. Go to the pit and check for scuffing on the sidewall, which requires more pressure. If not drop a few psi and go for another short session. Note if the car has "more grip". Back to the pits. Repeat until you find the optimum pressures. Wait until the tires cool down and measure the air pressure. Now you have the starting cold pressures for your tires and setup. Professionals have temperature meters to measure tire temp. across the tire width. They try to get equal temperatures across the tire, i.e. equal use, best optimal grip of the tire.

 

thanx guys for the help

 

Randy Chase (National C stock SOLO champion) reccomends running RA-1s at Very high pressures (low 40s cold, high 40s hot). He was one of the only guys to compete with RA-1s against everyone else running Hossiers and his results speak for themselves. I run my RA-1 at these high psi and they work well, I have pretty even wear too. The sidewalls on the RA-1s are extremely soft for an R compound, I can't even imagine running them at 18 psi, I would be afraid they would roll off the rim (but than again, I have never tried this so it just my guess). Another frequent track guy (on S2ki) running S2000 with RA-1s who happens to be a former Toyo employee also recommends much highr pressure with the RA-1. I have not played around with lower pressures much because of the squirm, it just does not feel right to me. I guess I should run lower pressures know that my tire is pretty worn down, perhaps the squirm will be less noticable now. I have 2 autoX this weekend, I run 43f/40r cold and then when they are heated up after 3 runs I'll drop the pressure f/r by 10lbs and see what happens for the next 3 runs.

 

I think it due to an autocross application vs. track application. A RA1 is essentially a track tire that requires a lot of heat in them to get sticky. The actual target pressure is around 40+ psi hot.

Autocross runs aren't long enough keep the tires warm enough, so not too surprised a colder pressure is required. That being said, I'm no autocross hotshoe, but haven't had any rollover issues at lower psi. Don't know if I'd be faster with high pressures, but I'm not that good yet for that to matter.

A track application requires a lower cold temp pressure, because of longer running time. I used to feel squirm too, but I think that was due to running without shaving off the rain blocks on the tire. Now that the tires are worn to the dry grip tread depth, they seem very stable under braking and cornering. Like autocross, I'm not really playing with tire pressure, just getting the driver straightend out now

 

Yes, there are differences between autoX and track tire set up. Randy said that essentually what works for one works for the other but cold pressures can be higher for autoX since they will not heat up as much as on the track. Like you, I tend to set up my car reasonably well and just work on refining my driving since I am not really consistant enough of a driver to be able to detect small changes in car setup. I have been using 41 to 43 psi cold up front and about 3 psi less in the rear and the balance appears to be pretty good with a 3 psi differential for autox. In terms of absolute grip, it may be that I would get a bigger contact patch with lower cold psi settings. At one point, during a 30 minute track session, I think I overheated my tires beacuase they got really greasy and I had to back off for a couple of laps. Perhaps starting at a lower psi would have prevented this. I also got my RA-1s full tread and I originally settled on the high psi setting due to the squirm and after I read a post from Randy Chase encouraging higher psi, I figured I may as well try it. Now after 3k street miles, 7 autoX and 2 track days I am down to 2-3/10s depth and perhaps I can lower the psi somewhat. One extra thing, I am getting pretty even wear (a little more on the inside from street driving and a little more wear from autox events on the outside to balance things out) with my current higher psi's.

 

I've got around 7000 street miles, 8 autocrosses, and 3 track days on mine with around 3 mm tread left and pretty much even wear. I have a 205/245 on stock suspension, UK alignment, which is more of a track setup.

On the street, typical wear on inside of tires, with the rears wearing more than the fronts.

Autocross, light wear on the outside edges and more wear on the fronts than the rears.

Track, heavy wear, more on the outside and rears.

In the end all four tires are equally worn from the varied uses and have lasted longer than my OEM SO2's. I really toasted the SO2's on the track and they were never the same, while the RA1's come back to at least 80-90% once warmed up. All in all a great compromise tire and setup, but giving up performance in autocross/track by having a "mild" alignment setting.