tire pressure???

[briham89]

I know this is going to vary by tire, but I am running Hankook RS-3s in a 225/45/15. And was wondering what is a good pressure setup for auto-x and track days. I raced an auto-x last sunday and couldn't seem to find a pressure I like. I was in the 30-34 psi range when i was there. Any suggestions? Thanks

[SkinnyVT]

Are those hot pressures? What was the car doing that you didn't like the pressure? I've never run those tires so I don't know what specific pressure works best.

[shiboujin]

I usually do 30 front 35 rear. But I drift....

[briham89]

yes those were hot pressures. I was over steering all over the place. Couldn't seem to give it some power with out the car wanting to drift everywhere.

[brodee]

In my M3 with 225/50-15 Hoosier A6 I was running 36-38 front and 32-34 rear. That kept it pretty neutral.

I just got 235/40-17 Dunlop star specs on BBS RK's so now I'm going to need to figure out pressures again.

[brodee]

Next time you go out mark your tires with shoe polish. You can mark 2 or 3 of the little triangles on each tire on the edge of the trim. Go out and make a run and then check the marks. If the pressures are right you should scrub down to the point of the triangle. If you are too low then it will scrub further, too high and it won't scrub down far enough.

[nando]

start out by using shoe polish or chalk on the corners of the sidewalls. if you are too low, you'll roll over onto the sidewalls and the marks will rub off. Too high and the corners of the tread will still have marks on them.

This varies tire to tire, according to your suspension geometry, by the course, on weather conditions, etc. etc. Nobody is going to be able to tell you what exact PSI to run, only ball park estimates.

as the tires heat up you'll want to bleed the pressure off to keep them at your "optimum". You won't really know at first, but eventually you get a good feel for it.

At that point consider a pyrometer, and set your pressures by tire temps instead. You want even temps across the tread. You can also tell if your geometry is right. Too hot on the outside and you don't have enough camber. Too hot on the inside and you have too much camber. hot/cold in the middle and you need to adjust your pressure. It's generally better to be a little hotter on the inside, than to be too hot ont he outside. You can also try it by feel but above a certain temp you can't really tell the difference.

[Adrian_Visser]

A pyrometer is different than a laser thermometer right?

[nando]

yes - but a real pyrometer is pretty expensive. I actually have an infrared/laser thermometer. laser thermometers are a nice intermediate step - I picked one up for about $30. As long as you measure right away, and get close, it works pretty well. You probably don't need a real pyrometer to be locally competitive.

[briham89]

Thanks for all the advice. I am going to the NASA/hpde March 20-21 so hopefully I'll be able to dial in some pressures there.

[CincinnatiKid]

I run around 31-32 psi for autox and slightly higher (mid to upper 30s) for track days, but I use two different tires. Ran RS-2s last season for autox, and RA-1s for track.