Tire pressure recommendations for DE with street tires?
 

I am doing my first DE in the 993 this weekend (have done several in other cars). I would eventually like to get some track tires to use but will be using street tires this time. I have 17in cup IIs with Sumitomo HTR ZIII tires (205 front and 255 rears) and was wondering if anyone has suggestions for good tire pressure on the track? Thanks in advance.

I would probably start at the recommended pressure on the door jamb and go from there. Those tires aren't known for the stiffest sidewall around, so you may have to go higher to keep it from rolling over. There should be small arrows near the crown of the tire, something like this:

http://racingready.com/wp-content/up...angle-mark.jpg

You will be able to see the rough area on the sidewall....aim to have it right at the tip of the arrow. Less pressure moves the line further down the sidewall.

A good pyrometer wouldn't hurt, either. You're looking for even heat across the inside, outside, middle of the tread if your camber is right. if it's higher in the middle, drop pressure and vice versa.

Sumi is a great DE tire. I would try to not exceed 38 PSI. Depending on track conditions and your skill, reduce pressure before going out accordingly.

Have fun tracking the 993. I just began putting mine on the track after many years of tracking a 1990 M3. I have found pressures on the door label to be WAY too high for a starting temp. On cool mornings of 40 F I start at 29 psi front and 28 psi rear. This will give me 35 psi hot temp. I've found pressures much higher than 35 psi hot are too slippery. I do this for both a street (Yokohama AD08) and R comp (MPSC) tire.
Have fun.

What size tires are you running?

I agree that the door pressures are way to high and that 29 psi is a good starting point for the front when cold; however, 35 psi hot in the rear is a bit low IMHO. The Sumi has a pretty soft sidewall and if the car is pushed hard at those pressures you'll get too much rollover. I'd shoot for about 34 hot in the front and 40 hot in the rear. Assuming the car has relatively stock alignment this stagger should give you a decently balanced car. If the rear gets over 42 hot the rear might feel a little loose. Have fun and be safe!

exceed 38psi hot correct?

I aim for 40psi hot all around.. the harder you push, the lower your cold pressure will be. Chalk to see how far you are rolling over the edges and changing\feeling pressure setup is a good way to fine tune.

If you are starting out, good street tires are the way to go. They are much more forgiving.

phil.

yes

AD08 are a great track tire two. I had two sets and hot pressures of 36 / 38 worked best for me.

Hi Scott,

the right hot pressures for your car will depend on the tire, the camber, your driving style, etc. As mentioned above you ideally want to maximize traction by having consistent outside, middle, and inside temperatures. You also have to watch sidewall roll, but increasing pressure to avoid this means you will have the center of the tread run hotter than the outsides, and this is not optimum for grip. So, it is a balance. Ideally, see if you borrow a pyrometer. If not, go by feel - is the car, especially the rear getting squishy?...too much pressure. Are you eating the sidewalls too far?...Not enough pressure, or pushing the car to hard.

As a data point, on my 18" PS2s I used to run 37f/39r hot. When I got a pyrometer, one day I found that 34f/34r hot gave me consistent temperatures across the tire for that day, with that track temp, that camber, etc. This resulted in 27f/25r cold temperatures.

I suggest you bleed off some pressure at the beginning of the day, and monitor/adjust the temp/pressure each run until it stabilizes.

Have fun and stay safe!

I run 235/40 front on 8x18 rims and 285/30 rear on 10x18 rims

thanks guys for all the input. I will bring my air tank and adjust as I go. Looking forward to the first time in the 993.

A good rule of tub from Tire Manufactures at the track sharing knowledge with DE folks, +/- 2 degree changes at one time.

Your goal is consistent hot temps, checking as soon as you get off the track. Then after a day of good temps / control feeling on track, then check the cold temps the next morning to figure out where to start next time. Do not forget to re-inflate for the drive home as hopefully you are not generating as much heat on the way home as on the track :)