This past Sunday I got to flex my Z a little bit with some Auto X. I had a ton of fun but I know I can definetly improve my times. Alot of it was my overeagerness with entry speeds but I also know alot of time was lost due to tire pressure. The event staffers (Equipe Rapide) were in a rush that day to accomodate a set of karters in the afternoon and we were forced to run 3 runs back to back. I had no time to make adjustments to my tire pressure which was a very high (40psi cold). I was experiencing a ton of understeer and corrected it with throttle imput but this resulted in alot of drifting/powerslides which robbed alot of time. I was wondering what I should do tire pressure wise. Do I lower the pressure in the front to gain more grip and reduce understeer?

Tire Info:

Kumho Ecsta Supra 712
235/45/R17 Front
245/45/R17 Rear

 

your going to want your car to be as neutral as possible. Find some chalk and mark the side walls to find out the roll over point. If you arent using the whole contact patch take some pressure out. If you are rolling over on to the side wall then you should add some pressure in.

Just some more basic tips, smoothness is key. There is nothing wrong with a slight drift in very tight turns. In long sweeping turns, definatley keep your traction.
This car will understeer a lot going into turns too hot. Do not brake hard WHILE turning, brake early and modulate the throttle through the turn.

 

What he said.

Glad to hear that you enjoyed yourself. The problem with autocross and DOT tires is that you DO NOT want to run on the sidewalls. Begin with 50 psi cold. Mark the sidewalls of the tires in several places with white chalk or paint. After a run, take a look at the paint. If the paint on the edge of the paint is undisturbed, drop the pressure a couple of pounds. After some trial and error, you’ll get it right.

 

40 PSI on street tires is WAY too low.

Start around 50 PSI or so. On street tires, I got the best times with the fronts about 52 PSI and rears about 48 PSI.

 

On the sidewall it says the max pressure is 44psi and not to exceed that. I'd be kinda scared to go over 44 and I still think 40 is too much but I still haven't done that paint/shoe polish test. Basically, if I want to dial out understeer I want to make sure the front has the largest possible contact patch (more tire pressure if rollover onto sidewall is present) and the rear should be overinflated to promote oversteer?

 

With a stock setup, you're going to have to adapt to a "slow in, fast out" technique. Take advantage of the car's excellent brakes to scrub off a little more speed before entering the corner.

When entering the corner, you'll have to be less agressive on turn-in than ideal.

You'll definitely need higher pressures.

 

Yeah I do think my entry speeds were too high, my driving style is more at home with a neutral handling lightweight, low powered vehicle. So I'll have to get some practice. I don't really know where to look for more auto x events so if you all could help me out that would be great. As for the tire pressure, is this something I could figure out by putting paint on the tires and doing figure 8s or it has to be done after an auto-x run? Basically, I wanted to figure out what my ideal pressure is before the run so I can make the most of my seat time.

 

If you've got little ones at home, chalk also works instead of white shoe polish.

I'm in Canada, but from what I understand there's a large Solo2 population in Florida.

 

I ran close to 55 PSI on our Intrepid's street tires (44 PSI max) when I ran that on street tires. I'm able to run less than that with DOT-R tires.

The problem is that you need to support the sidewalls. Most street tires have very soft sidewalls, so you need to increase the pressure to prevent the tire from rolling over onto the sidewalls.