Had my first autocross

[John_D.]

It was a blast. Best time was 1:00. Had a DNF, 1:03, 1:04, 1:11 (full lock in a very slow tight right turn, set up wrong somehow, would have run over the last cone, stopped, backed up, took off again), and then the 1:00. Best time I saw anyone one run was a :53, the guy with the Skip Barber racing school t-shirt, v-8, and awesome tires.

Watching the video afterwards, my car was so quiet and looked so smooth. (the v8 cars were way loud).

But I know it wasn't as smooth as it looked. The tires were scrubbing like crazy, with a lot of understeer, especially noticeable on the slalom. I remember going almost full lock a couple of times to hold the line I wanted, thinking I must have been loosing a lot of time doing all that scrubbing. You couldn't tell it at all from outside the car though. Looked a lot smoother than it felt.

Also there was a *LOT* more body roll than I expected (watching the video). They thought I was going to take the ground effects off on the u-turns. I think I was the only one with ground effects, come to think of it...

Definitely time for some 1LE's and the STB.

And I will have to try 40psi next time, instead of 35. Since I was going back and forth between the strip and the autocross, I split the difference and ran 35 psi all day. Not optimal for either type of racing, but what the heck, I had fun.

Oh, and I had to take the t-tops off to wear the helmet. That, or scrunch down in the seat, and slide the seat back further.

[MustangEater8251]

I need ot video myself too see how I do. I let a guy that got me into it drive my car, his is down, and he paid my entry fee. he is trustworthy. It was great, got to hear my exhasut WOT, sound alot better then I thought, and I too noticed body roll. I have poly bushings and 1le bars in my room right now, but I amstill waiting on a BMR STB, if it doens come tomorrow, I am gonna have to make some calls, or posts here ot Lmperformance, its taking alot longer then it should.

It is a blast though. You may want to keep the t-tops on and adjust how you sit. I adjusted how i sit, being 6 foot 5 in. and a helmet do not work, felt wierd first itme i wore it. It is a blast. Even if you have the worse runs of your life and spin out, its jsut as fun [img]smile.gif[/img] . Also fun to see ome cool cars, a guy with a 2002 Z06 runs at mine, a couple NSXs an M5, its nice to see some nice exotic cars running full hard, losing the tail end, instead of cruising at 45 mph on the highway.

[MustangEater8251]

by the way, I am also looking inot a set of autocrossing tires. i found a guy wlling ot gve me 4 16X8 steel rims for free. I jsut need the money to get the tires. I had some understeer problems 2 autocrosses ago, but last one it wasn't as bad, but it was a pretty straight course.

[John_D.]

I know what you mean about the tires. I saw a lot of Kumho and Nitto tires there. I'm thinking about getting a set that I can just run all the time, so I don't have to switch back and forth.

That way I'll have the same handling when I'm just driving around. And they look good too.

[V6Bob]

Withe regard to using the same tires. Real "autocross tires" (even ones legal for stock classes) are worth at least a second and maybe as much as two or three. Obviously your choice, just some facts for you.

You can adjust the understeer/oversteer balance by tire pressure. Run the end you want to stick better a little softer (2-4 psi) than you would think, keeping the other end pretty hard. IOW, you were thinking about going from 35 to 40. Try it at the rear only for starters to kill some of the understeer.

[John_D.]

<blockquote>quote:</font><hr>Originally posted by V6Bob:

You can adjust the understeer/oversteer balance by tire pressure. Run the end you want to stick better a little softer (2-4 psi) than you would think, keeping the other end pretty hard. IOW, you were thinking about going from 35 to 40. Try it at the rear only for starters to kill some of the understeer.<hr></blockquote>

Ok, I'm confused now. I thought the higher pressure kept the tire sidewall from rolling under the wheel, while cornering, keeping the tire vertical and the contact patch flat on the ground. If that is the correct concept, it seems the end of the car with higher pressure would hold better, and the end with the lower pressure would drift more.

Unless the tires/suspension is not capable of putting enough side load on the tires to roll them under. If this is the case, then I can see that more inflation would only round up the sides of the contact patch, as the center of the tread pushed down and out further, as a result of the added inflation pressure.

I was going to chalk the sidewalls and see how far up it was rubbed off, but I forgot to. The rubber was scuffed about 1/2" up the sidewall, but no further.

And actually, I ran 36 in the fronts and 35 on the rear... Not much difference, but I didn't want to go any higher than 35 on the rear and still try to drag race it too... But thought I could get away with 36 in front, driving it 60 miles to the event.

Sounds like I will have to experiment, and see what works best.

I'm looking not only for balance between front and rear, but more overall adhesion. It just felt like the car should have taken the corners a little more affirmatively.

From daily driving, I know at 30-32 psi the tires give up, a whole lot more easily, compared to 34-35 psi.

[John_D.]

<blockquote>quote:</font><hr>Originally posted by MustangEater8251:
You may want to keep the t-tops on and adjust how you sit. I adjusted how i sit, being 6 foot 5 in. and a helmet do not work, felt wierd first itme i wore it. It is a blast. Even if you have the worse runs of your life and spin out, its jsut as fun [img]smile.gif[/img] . Also fun to see ome cool cars, a guy with a 2002 Z06 runs at mine, a couple NSXs an M5, its nice to see some nice exotic cars running full hard, losing the tail end, instead of cruising at 45 mph on the highway.<hr></blockquote>

6' 5" !!!!! And I thought I had to scrunch down... I ran both ways. My head was sticking out when the tops were off.

It was a lot of fun. Almost of the cars at this event were f-bodies.

There was a ZR-1 that pulled up while I was checking my tires on a break, and although he was just meeting somebody to watch the drag racing, I think he decided to try the autocross after we talked for a while. Looked like he was in line when I was leaving for the day. The tires on that thing made 2 of mine...

There was a Nissan, 240SX I believe, that ran a few times. It was even quieter than my car.

I wanted to see the girl run the red Miata with the supercharger, but she didn't race, something about her car was acting up.

[V6Bob]

"Ok, I'm confused now. I thought the higher pressure kept the tire sidewall from rolling under the wheel, while cornering, keeping the tire vertical and the contact patch flat on the ground. If that is the correct concept, it seems the end of the car with higher pressure would hold better, and the end with the lower pressure would drift more."

On a real race car, with race tires and super adjustability, you are right, you try to keep the contact patch flat with tire pressure and adjust other things. Autocrossing or racing a nonadjustable street car you use the fact that tire pressure changes the effective spring rate too. Tire pressure effects are way complicated. If your car is unbalanced it can be worthwhile to give up a bit of ultimate grip at one end for better balance.

Note that I said _try_ this. It might surprise you or it might not work. If you're worried about rolling the fronts under at 35/40, try 40/45.

[John_D.]

<blockquote>quote:</font><hr>Originally posted by V6Bob:

Note that I said _try_ this. It might surprise you or it might not work. If you're worried about rolling the fronts under at 35/40, try 40/45.<hr></blockquote>

Good point. That's why I said "Sounds like I will have to experiment, and see what works best."

The 45 sounds a little high though.