Race tire question.

[erok]

I used my new Victoracers at the Streets of Willow Springs a couple weeks ago and the fronts were signifigantly more worn afterwards than the backs. Especially on the outside edges. The backs still look almost new like this |__|, but the fronts look like sorta like this |__/.

I like the idea of rotating tires between events, but at the autox last Sunday with the worn tires in back, my car was very tail happy at the limit. I ran the fronts between 40-45 psi and backs at 30 psi and still it could have used more grip in back.

Should I just keep the worn tires in front? Or lower the rear pressure even more? Camber is at -1.5

[NSX_GTR_LM]

I think your PSI is a little high, cause 45 is like 15 above whats reccommended (i think). 45 is pretty damn high. Also,. the reason the car is ass happy is because you are sticking some beat up tires on the back, goving more traction in the front, causing oversteer. Your car is a celica I assume, and since it is a front wheel drive car, it is obvious why the fronts are going to be torn up over the rear. The front does nearly all the work (accellerating, 90% of braking, steering, etc). so a negative camber of 1.6 in the front will show up alot quicker than 1.5 in the rear. By having this pretty negative camber in the front, your tires are gonna get beat on alot more than you might think. An alignment would probably be a good idea.

i think you should invest in a swaybar set as well to cut down on some of the roll. I front and rear swaybar set from hottchkis will run you about $300, and you will probably see more benefits from this than from lowering.

Others please feel free to correct me if I am wrong on the tire deal.

[autxr]

Others please feel free to correct me if I am wrong on the tire deal.

OK, I'll correct you because you are wrong.

Racing tires and street tires are different breeds, tire pressure printed on the door frame are for best miles per gallon and a comfortable highway ride, they have no real bearing on what is best for performance.

The tire wear erok reports is pretty normal for a street car. I don't think it make a lot of difference if you rotate the tires, i'd say you were loose because autocrossing is much different than track driving, the turns are *much* sharper in general, and that is part of the difference, a good track setup is not a good autocross setup (often times).

Several things to do...

Lower rear pressure more. I've gone as low as 17 psi in the rear. It isn't ideal, but I didn't have any problems. It also did solve my oversteer issues.

Adding more negative camber up front will help with the tire wear, but it may not help with the oversteer...

What mods do you have again erok? Or are you running stock class for autocross?

Springs and sway bars can help with the oversteer, so can a different alignment and changes to the big nut behind the steering wheel ;)

Back in my "I'm going to spin every run" days, I had a nasty habit of braking too late and turning in too hard - at the same time. Since then I've learned to get my braking done before turning and now I rarely spin, except when the nut behind the wheel gets messed up.

Make sure you get to the right speed before turning, then hold speed or accelerate out of the turn. Significantly fewer spins will result.

If tire pressure and driver changes don't help, then look to the alignment. Get some toe-in added in the rear. B1mmer (from the autocross forum) has played with as much as 1/2 total toe in! He reports a very stable tossable car. You can set it easily on race day then put it back before going home. Ask him over on the autocross forum how many ticks on the adjuster coorespond to the 1/4 inch per wheel.

Playing with negative camber in the rear also helps, I've seen huge differences in numbers, I prefer less, others prefer more (I'm at -1.3 deg rear and -2 deg front). Less negative camber (in theory) gives more contact patch under braking and on turn in. After the suspension is loaded up, you might overload the tires with too little camber (not a problem for me). Less camber most certianly added stability to my car (I noticed the difference between -1.7 degrees and -1.3 degrees, I spin less with less camber). The rear suspension is very good, the double wishbone setup has excellent camber gain under compression, so you don't need to do much to overcome body roll (unlike the front).

Scott

[NSX_GTR_LM]

hehe, thanx autxr. I knew you would eventually be here

[erok]

I have the TRD Sportivo suspension kit on my car. This includes shocks/struts, springs, sway bars and the bushings that affect the passive toe-in in the rear suspension.

Next event, I'll try lowering the rear pressures more. When I feel like blowing yet more cash, I'll try out some different alignment settings. Maybe I'll put the Victoracers on and try some street experiments since the next event is a month away.

Thanks autxr.