pitchadude

I am autocrossing my 1995 C4 and have Nitto 555's. The first time I ran I used the "start up" 40 psi but today I ran 39 psi. How much can I lower them and be safe but effective.
Thanks for helping

93Rubie

Run 40 in mine with good results. Biggest thing is that you don't roll over onto the sidewalls. So if you have to mark the edges of the tires of with caulk or something run the car and see if you need more or less psi. Can go right up to the edge of the sidewall but not onto it.

Bill Dearborn

I think that pressure is way to high. When I ran my 86 I started with those high pressures and had poor results. I finally found the car worked great running the old GY gatorbacks when I started at 33 psi front and 30 rear cold pressures. Then I adjusted tires up or down a pound or two from what ever pressure reading I got later on in the day to fine tune the car.

Bill

l98tpi

I have been running Hoosier A6's. When they were newer I would run 30frnt/26rear, but as they aged I had to increase to 34frnt/30rear. Not sure if this is the norm, but I watch the roll over of the tires as well and adjust accordingly. In a different car with Kumho V700's race compound/ rain tires I run 38frnt/34rear. These pressures seem to work for the tires and alignment on my car, you may have to test yours at different pressures and see what works.

Aardwolf

Each tire is different but that does sound way to high. A higher pressure may have crisper steering response but lose ultimate traction.

I start mine at 25 cold and usually let quite a bit as they heat up. I'm going to try 30 hot at my next event.

I read a study awhile back with A6's from 20 to 50 psi hot. Ultimate grip was at 30 with their test car. Tread roll over started at 40. There was a .03 g gained from 40 to 30 psi. Whether the addition small g can help you win with the reduction in steering response is up to the driver I guess.

shakedown067

Street tires generally require more pressure. My last event I ran mine at 41 with great results, but it was in the rain...they also aren't the best and have a slightly spongy sidewall, so higher is better for me. I agree with 93Rubie, use chaulk to find your tires optimum patch width. My guess though with the Nitto 555's, would be in the mid to upper 30's.

Tim T

I am running NT555RIIs (275/40-17s on 9.5 inch rims) on my 93. Usually run 38 front and 35 rear.
I use chalk marks when autocrossing

1991Z07

An infra-red pyrometer is how I check my pressures. Adjust the pressure until you get a fairly even temperature across the width of the tread. Check it right after a run...then you'll get your cars "sweet spot".

Each car is different based on alignment settings, and this is how the pro teams check their tire pressures and alignment settings...too high in the middle of the tire means too much pressure. Low temperatures in the center means the pressure is too low. Adjust in 2 lb. increments until the temps are fairly equal all the way across the surface.

BrianCunningham

What's your alignment?

That's really going to effect how the tire reacts to different tire pressures.

93Rubie

I should have stated I am running on Kumho Escta SPT's which are street tires. I can tell how much I roll over on the tread just my looking. 40 is about perfect for me. I had a guy who does a LOT of auto-x with C4's run my car with me riding shot gun. He took the marks on the tread right up to the edge of the sidewall at 40psi COLD. He didn't seem to think I needed to mess with it, he said the car for street tires sticks pretty good. Lets face it, if your a relative newbie like me, tire psi is not very critical to good times unless it is WAY off. Seat time is more important, that is why I focus for now on not letting the tires roll over onto the sidewall. As I get better I might then start to mess with them some. I would think tire pressures would vary driver to driver in what you like and/or prefer in a car. Track to track too...IDK???

shakedown067

Very true, you'd need to run more pressure on a stock alignment vs running an advanced alignment. A good autox/street alignment helps a lot and effects more than tire pressures. Especially since C4's come stock with .5 POSITIVE camber. I still scratch my head at that one...

pitchadude

stock alignment

BrianCunningham

1st thing is to get rid of the stock alignment, that's most of your problem right there!

Here's a good reference

http://www.vbandp.com/View-document-...ent-Specs.html

Advanced street won't kill your tires, you actually get better wear with it.

l98tpi

93Rubie

I setup my car with a cross between VBP's street and advanced street setup. I did not want too much rear camber as I do see some drag strip action. Make sure you torque those rear eccentric bolts down good. I have some trouble with mine moving on me. NO complaints so far.

Bill Dearborn

I still stand behind my 33 front and 30 rear cold pressure setting. Worked great for me and I had bunch of FTDs in both NCCC and SCCA autocrosses (not counting a couple of E and F mod single seat cars).

Bill