I'm going to autocross my '05 for the first time this weekend. Bone stock. I haven't autocrossed in years and really don't plan to make it a habit (again anyway, famous last words...), but would like to do as well as possible.

Given that I'll only have a few runs to dial in, can anyone recommend good starting tire pressures? It's a mall parking lot so I'm expecting it to be pretty dirty blacktop and weather is expected to be partly cloudy and in the 60's.

Thanks much for any information.

 

If you're bone stock on street tires, I'd recommend starting somewhere around 35-36psi all around. This'll keep the edges of the tires from being chewed up and help stiffen te sidewalls some more (over the factory settings of 32 psi all around).

Good luck!

 

Thanks, appreciate it (and my sidewalls thank you!).

 

I found that it was rolling over at those pressures, and I am wearing out to the edge of the tread running 42-44 psi on my proxes 4's. This so far seems to be the optimal setting for me. In general, from what I understand, you want to run ALOT more pressure in a set of street tires for autox vs street driving. (Not to mention the fact that it's easier to take a couple pounds out, then to add it back in!)

 

Thanks, I'll let you know how it works out

 

I'm on the factory tires right now and have a few events under my belt. Right now I'm experimenting with 38psi front and 35psi rear and going from there. I'm afraid that if I pump up the rears too much the car will start to get tail happy. I have like 0 experience with differences in tire pressures.

 

Well, I ended up using 40.5 psi all around to pretty good results. The course was pretty tight and short (about a 40 sec run) and the biggest problem were two areas, one an off camber uphill 'sweeper' that loaded the left front tire and the other a tight transition back and forth that wanted to get the tail wagging. So I figured to go even all around and that pressure seemed a good choice for both ends of the car and didn't roll the tire wear onto the sidewall. The best part was that, with a fairly small field (probably 50-some cars) and the short course, we got eight runs, so I had a good chance to improve through the day.

And what a fun car to autocross! It's so well balanced, tight handling and an engine that you can pretty well use to red line without worrying about valves kissing pistons or rods coming out the side of the block! My son ran the car a few times as well and just loved it compared to the Eclipse or 240 SX he usually drives.

The only problem was I really had a great time, and even after about 20 years away, starting thinking about the next time!...

 

Since I just got this car and got to take it very successfully autocrossing for the first time last weekend.

Running (out of manufacture) 2007 Bridgestone Potenza RE-01R's 225/45/18's with decent 1/2 tread. 180 tire wear rating

Best times back to back hot over 6 near minute runs on concrete were achieved with 41F - 38R psi and with 10 minutes between runs the pressures stayed constant on a 75F sunny day. I just got a new tire gage which shows my old calibrated gage to be +2psi making my "optimum hot pressures 39-36 on the new gage. **What I always said is stick with the same gage for the season.

Sixty minutes after running the pressures were 37F - 35R. When completely cold they went down to 36F-34R with 60F temp. later than evening.

In the morning at 40F outdoor temp they ended up at 34F - 32R. Now that would be definately what I call a cold tire.

Will eventually move up to a 245 tire when these are worn out and will start test all over again.

 

I am currently transitioning between the stock tires and the Dunlop Star spec which everyone advised me to buy. I got the 245/40/18 which I put on the back. I have been running around 40psi up front and 39psi at the rear. Since getting the star pecs on the rear I knock 3 seconds off my lap with 2 good tires and 2 crap tires up front, I was getting a bit of under-steer but I found on a long curve that if I planted the power the car would rotate a little and have a nice power slide round the long sweepers. I did get a bit confident though and ended up backwards once.

 

Start at 40 and chalk the edges at 6 points. When you are done with the first run you will see how much roll you get by seeing how much chalk is gone.

 

I prefer, on stock tires (measured cold):

-Dry: 35R 35.5F
-Wet: 36.5R 37F

R-compound:

-36R 37F

 

and you are not rolling with those stock tire pressures?

stiffer on wet? Don't you want more give on wet so you don't break lose?

 

Sounds totally plausible to me as your tire gage is probably "correct" in that psi range. Thanks for the heads up on R tire pressure and wet too!! Some recommend increasing up to 10psi in the wet to fight hydroplaning and squirm but I've never been a follower of that logic. I suppose they are assuming one is using "full depth tread rain tires" meaning they actually have two full sets of tires at a regional event.

 

aka, "the slow way 'round."

seriously, get the same tires for the front.

 

[quote=dmitrik4;3833721]aka, "the slow way 'round."

Yea, leave that to the D shows. That is strictly for show not GO. Losing traction because of drifting loses forward momentum. It's almost as bad as plowing the front end and it can be likened to spinning the wheels on a launch.

 

You want higher tire pressures in the wet for two reasons 1) hydroplaning as mentioned and 2) since I like to measure the pressure cold and that the tires don't heat up as much in the cold

Those numbers are my personal preference. They are the result of the chalk test + the g-circle test + my own style of driving. If you have time, I do recommend you run your own test. Chalk test is when you mark your tires with chalks to see contact patch at different pressures, g-circle test is when you go around a circle of 40-60 feet radius and gradually increase the speed to see if you understeer or oversteer. And finally I prefer a little understeer since I have the bad habit of late braking and I started autocross with fwd.

 

Concur, I mentioned the chalking not too far up on this thread.

 

My Hankook Ventus V12's have tiny little arrows that point to the optimum scrub line as many other tires do.

I wouldn't know how to read the chalk line, but the tire engineers probably know the right spot!

Whether I'm autocrossing or tracking, I shift my mind set to hot pressures, and it seems that I always liked about 44 psi front 40 rear measured right after a run on just about any tire I ran.

 

yes, use those arrows. take the chalk line pass the arrows. If the chalk is gone pass the arrows then you know you are rolling over the arrows. Otherwise you will not know you are doing it till the arrows are eaten away

 

Currently not a fan of those tires. I run them as well but they drive me nuts. What pressures do you run?

 

A newb "death plow" will suck a front tire under, and some Initial D super dorifto will do the same to the rears. I'll wear the chalk / shoe polish off more than you would get if you were driving correctly.

You'll get the best results from chalk lines if you drive at about 90-95%, not the 106% I normally drive at.

Check and recheck often, too. Optimal pressures differ with tire model, tire wear level, course surface, tire temp, ambient temp, surface temp, and about a million other factors.

It's not unheard of for the OCD type drivers to actually use different pressures on every corner of the car depending on course layout at each event. We've got at least three that keep detailed logbooks and notes that I see going right to the air tank after course walks.

Me, I haven't checked a pressure before an event in years.

 

Yeah, I'll admit these are the weirdest feeling tires I've ever run, but they're cheaper, track straighter, and grip sooner and better than the SPT's I replaced.

They feel like they have a hinge or fold point right at the edge of tread, whereas most radials have a very stiff crown there, and the side wall is the soft point.

Like I said, I seem to always come back to 44 hot front and 40 hot rear, and these tires need more than most others.

If you actually get the car to oversteer, then run 40-42 or 40-40.

 

OK, now I get it! I always checked how much the tire was being chewed up.