AutoX Starting Tire Pressure for an SC?

[Noel]

I am planning to run my first autocross in my new SC. While I have been autocrossing for years with a 300ZX with G-Force race rubber, I plan to use the street Bridgestone RE71s (205s & 225s)for this event. (on 16"x 6/7" Fuchs) What starting tire temps should I use for this car? Would simply bumping the recommended front and rear pressures up by 5PSI be a good place to start?

BTW, the car is very much stock and even has the 1980 stock ride height.

Many thanks,

Noel

[jrdavid68]

Here is a good thread to read on this very subject:

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=30638

JrDavid68

[Randy W]

Noel, I would recommend your starting pressure for autocross be the pressure you want to end up with or maybe 1 pound lower in the rear. For autocross in the dry I would start RE71s at 27F/30R, and bleed as needed to 27/31. In the rain I would start at 25/28.

[gslater]

I've always autocrossed on street tires, both with my SC and other cars. I have the Dunlop SP8000s on my car, and I usually go with 35 front, 40 rear, or perhaps a few pounds lower on both ends. That's higher than some people like, but I prefer it that way. For me, the main thing is to maintain roughly that 5 PSI factory recommended differential front to rear.

[Superman]

I like 36-38 rear and 31-33 front. Tires will be at least 3-4 lbs higher after the first run than they were before the run. But let me add this: Randy W has forgotten more about autocrossing than I may ever know. Of course, my car outweighs his by probably 500 lbs.

[Noel]

Randy,

I must say that I am alittle surprised with your low pressure recommendations. Is there something about the RE71s. I always recommended to others starting out to raise the pressure of "Street" tires.
Can you explain futher.

Noel

[Randy W]

Noel, I think this difference in recommended tire pressure is a matter of taste, based on driving style and what is most important to the driver. For the track, I would agree with the general rule of raising street tire pressures fom what you use on the road, because of the sustained side loadings encountered. For autocross, compliance becomes a more significant factor. I have found these lower pressures on the RE71 allow better traction and faster times at the expense of some directness in steering response. You may find after trying different pressures that the lower pressure does not give you the feeling of being as connected to the road, and responds poorly to overdriving. RE71s have a relatively soft shoulder, so you would expect them to perform better at higher pressures, but for me they are not as fast that way. If you have the opportunity, try them at the two levels of pressure recommended, 33/38 and then 27/31, and see which one is fastest for you. It may be that something in the middle, say 29/34, will give you the best compromise between driver confidence and traction.

[Noel]

Thanks again Randy. I will try the lower pressure as you propose. However, since I will not have an air tank with me, I will reserve the last couple runs to trying the lower pressure.
I totally agree about the drivers' tastes being a key factor. I do know that I find I am faster with a slightly looser (Oversteering) car. (For autocross only). On the track I prefer the reasuring feel of a little understeer.

I look forward the to the test.

THanks Again,

Noel

[cary]

Thanks for the info. 27F/31R worked just great yesterday at about 80 degrees outside.
I still a have little tOOOO much brake for the street tires.
I'm going real fast with the short gear box. Not leaving enough space for braking. Need more seat time....

Randy, once again, thanks for for your input.

[Randy W]

You're welcome, Cary. Glad you had a fun day.

[Vipergrün]

Yikes, this thread got me thinking about the understeer on my 80SC with 225/50's front and 245/45's rear running RE730's. I checked the cold pressure and they were 22 front and 24 rear. I guess I was getting too much sidewall roll? I put in 28 front and 32 rear, makes a big difference. I had not checked the pressure since the tires were first mounted (a no no). What are recommendations for general street use?

Thanks much
-Brad
80SC

[Superman]

Again, I like higher tire pressures. I don't think you give up any adhesion and you get a little more torque and better fuel economy. Factory says 29/34. I like 32/37.

[cary]

On the road I run 31F/35R with my RE-71's.

But they went to 35F/40R in my first A-X run two weeks ago. Which gave me an ugly push on 90 degree turns. ( But it still might be right foot related )