JustinL

I seem to have found a plateau in my autocrossing times around our local course. My next step is dialing in tire pressure, but this seems to be somewhat of a black art. What I'm looking for is a procedure to nail it down.

Here's what I have right now: 4 245/45/16 Fuzion ZRi on 16X8 wheels. Current tire pressures are cold 32 front, 34 RR, 32 LR. There are fast lefts and slow rights on our course. The tires will warm up, but there is a marginal increase of maybe 1 or 2 psi in pressure after 2 laps (approx 110s). There is no rollover onto the sidewall. And almost no heat getting into the LR tire.

The lack of pressure increase and sidewall rollover would suggest lowering pressure further, but do I dare go under 30psi. I've read that 40 hot is the golden rule for race rubber... this doesn't seem to apply to street tires.

Any help would be appreciated.
Justin

Edit-- This is for my 87 944 NA. It feels nicely balanced to me right now, but I'm still in my rookie season.

Mongo

i've had the most luck running 36 starting all the way around. Then when the tires get hot after a couple runs and pressure builds up to about 42-43 I let some air out, about 2-3 PSI to take it back down to 40. MY rears were 45 one time so I took them to 41.

Ending tire pressures after they cooled were 34 front and 36 rear.

M758

Toyo RA-1's like 38-40 psi for the race track. I stat them at 32.5 psi cold and they heat to 38-40.

Autocross is very different since most tire don't heat up anywhere near as much. 36 is solid starting point. I would keep all pressure the same and move up/down 2psi until you fine what works for those tires.

JustinL

I found that I was sliding quite a bit and slower at 38psi. I've been reducing pressure and it's gotten stickier and faster, but what I'm after is some sort of indicator that I've found the right pressure. Should I keep reducing until I see sidewall scrub then put a couple pounds back in? I'm worried about going too low. I can borrow a pyrometer next time out, but I wouldn't know what to look for.

Teach me

Justin

M758

Well you will know based on lap times and feel. If however you are still learing in leaps and bounds then getting pressure OK is the best. I really only learned to feel how tire pressure changes the car after years of autocross and track driving.