Broncs

Hey I competed in my first auto cross event a couple weeks ago and I am hooked!!!! By the end of the day the car was very loose I mean driving on ice loose! I have come to discover that due to the outside temp and tire temp I probably had to high of air pressure! What air pressure should I start with and should I check the air pressure before each run?

Thanks

ltborg

Most of us check pressure before each run.

As for pressures, what tires do you have (type, seizes, etc)? How much does your car weigh?

Broncs

Well it's a stock 88 and now I am running 275/35 18's on the front and 295/35 18's on the back. The tires are Nitto NT05's. these are not what was on the car last time.

ltborg

Not knowing what the Nittos like, I'd say shoot for low 30s and tune the balance from there.

l98tpi

I run Nitto NT01 for practice and run 34frnt and 30rear cold pressure. Look at the tires after each run and see how far they roll over to the shoulder edge, which is usually marked with a triangle or some type of indicator. If not rolling over enough, let some air out, maybe just 1 or 2psi and re check after next run. And at some point if you haven't already, get a agressive alignment.

ltborg

Be careful about that. The triangles (or whatever other mark is used) just locate the wear indicators in the tread, they are not actually designed by the tire manufacturers as a "roll over indicator." A lot of companies are now using company logos (Wingfoot, Michelin Man, etc.).

You can usually tell when you are rolling so much you are getting into sidewall rubber, which is too much roll:

• Very high breakaway rates near the limit (tires feel unpredictable)
• Visible line where the tread/sidewall meet (the two compounds wear differently and end up two different shades of black)
• If there is no line (the tread rubber wraps around the shoulder sufficiently), you need to go by handling, not wear

I've seen this last example in two different forms on the race tires I've used. On the Goodyears, dropping the pressure causes the tires to roll over what might be considered about 1/16" too much. However when you continue to decrease the pressure, the roll over doesn't get worse. I dropped the pressures almost 15 psi from that point before the handling started to go. Ultimately I gained over a second on a 30s TNT course going with the lower pressures. That said, on Hoosiers, when the wear shows up on the sidewall, I've found the pace might be there, but the handling isn't as crisp as it could be. The Hoosiers seem to need a little more pressure than the roll over method would tell you to use.

Hope that helps.

hklvette

On a C4, I'd start at 33-35 front, 30-32 rear. On my C5, I use 30 all around, and will adjust pressure to keep them there from cold to hot. My alignment is -2 camber front, -1.6 rear, zero toe on both ends. The biggest problem you'll find with NT05s is that they need heat. Lots of heat. Like 95 degrees and back-to-back runs heat. I've read that Nitto has stated their operating temperature to be around 160-220F, and have seen evidence to support that claim first-hand.

Zenak

Did you check here?
http://forums.corvetteforum.com/auto...e-learned.html

KBoltz

I run Toyo R888's on my C6 with the following mods:

Pfadt Inverted Sport shocks
Pfadt Adjustable Race swaybar
C6Z06 Springs
C6Z06 Brakes
TSW Nurburgrings

My tires are Nitrogen filled. I start at 32 front and 30 rear. After two runs near the 1 minute mark, I have to bleed the fronts down about 1-2 psi. After four runs, I have to bleed off the rears by 1-2 psi and maybe the fronts.

Now, my car is driven by my wife and I both, so this last session we had a total of 9 runs EACH with the Autosports Northwest Group. I have an air tank filled with nitrogen, so to get back home I may have to add some to keep the tires optimal. I do not swap out tires and wheels anymore. I may not get the grip of R6 or A6 Hoosiers, but I don't have to swap out wheels and tires or trailer the car to events either. I am getting lazy in my old age. ROFLMAO