KOAN

I am driving a new car (to me) with several new variables, and I hope someone can give me some suggestions about what is causing the problem, and how to fix it. The car is a '96 993 with PSS-9 suspension, "18 wheels with Hoosiers245/285, 40 lbs hot(2-3 yrs. old, good tread), shocks set on "1", sway bars middle/middle, -2 degrees camber F/R.
Track surface dry, cool.
During a moderate speed sweeping turn, the car oscillates side to side instead of oversteer drifting, seeming to gain and lose grip on the outside tire. The condition was reduced when I tightened the shocks from 2 to 1, and when I zeroed in on the tire temps from 44 to 40 in the rear.
Is this a consequence of Hoosiers overinflated? Is it an indication of too soft sway bar setting? Is it the spring/shock combo? I'm planning to increase the sway bar rate front and rear to see what effect this will have. Does anyone have any suggestions? <img src="confused.gif" border="0">

Dbltime

Two to three year old Hoosiers? You better order a case of Formula V and treat those tires ten times or so to try to soften them up. Honestly you should probably toss them and get some new rubber.

KOAN

Bill,
Thanks. Having never owned Hoosiers, and having never had other R compound tires last that long, I was wondering if that was the cause. Do you think this may have caused the uneven grip? And do you think any treatment will bring them back?

Mike A.

Bill is right, order new Hoosiers.
-2 camber on all fours doesn't sound right for a 911. The heavier rear will need more neg. camber than the front. Check tire tempertures after several hot laps (not pressure) to get a handle on what changes to make. You should have a good 4 wheel alignment and corner balance. Also, Hoosiers need to get up to 180 degrees for optimal grip. Good luck.
P.S. Bill, how do you get a picture of your car as an avatar under your name?
Mike

James Achard

Chuck, Bill is right on about the tires. Chuck them. If you plan on sticking with Hoosiers(No pun intended), you will need 3 deg. neg. camber to get the full benefit out of these tires. Also, in regard to your swaybars, drive the car at the track with them disconnected and see how the car feels. If it feels pretty neutral then re- attach the links and set the front to full soft and the rear in the middle. Take it out again and see how it feels. I would definitely get the car corner balanced and aligned before you do anything else as this will drastically affect what you do at the track. It's the best way to insure that all that you do at the track is not being obscured by a poor alignment. Cheers and good luck

James

KOAN

Thank you all for the feedback on the age of the tires. I've had it aligned and corner balanced, a few weeks ago when I put in the PSS-9 suspension. The M030 bars are equivalent to the RS sway bars in size, so middle/middle should approximate the stock set up. The car is a little loose, which is what I prefer. Stiffening the whole ride, while keeping the front/rear balance as it is will be the goal with experimentation with the bars.
Unfortunately, I can only get -2 degrees with the stock mounts. I'm sure more would be better, but I may have to go with other R compound tires to keep the car comfortably streetable and reasonably trackable, adjusting the shocks between events.

mark911

[quote]During a moderate speed sweeping turn, the car oscillates side to side instead of oversteer drifting, seeming to gain and lose grip on the outside tire.<hr></blockquote>

This can be caused by the kinematic on the rear being off. Make sure your shop can handle the kinematic adjustment. If they do not know what Kinematic is, then find another shop.

Mark S.

Hank Cohn

Chuck:

You got some good advice. Throw away those tires and get some new ones. I like 3 degrees of camber in the front and about 3.5 in the rear. I think 40 PSI is a little high for Hoosiers, but only by 2-3 pounds. I usually run about 38 hot. Alignment is very important as well as corner balancing and ride height. It is never a very good idea to chase suspension settings on old or unknown tires. Only make changes with good tires.

Hank

KOAN

How long should Hoosiers last, assuming they have been heat cycled appropriately, and still have tread (so to speak)? I called Tire Rack, and found that the tires I have now were delivered to the PO 2/01, not as old as I thought. Are they still too old? I'm taking my car back to get re-aligned to as much neg. camber as possible, ( as close to -3, that is) and to have the kinematic toe checked as well.

Hank Cohn

Chuck:

Tire life depends on a lot of variables like how many heat cycles they have been through, were they properly heat cycled on their first session, how heavy is the car, how hard are you driving the car, what is the surface of the track like, what tire pressures you are running, what alignment settings you have, etc.? The tread really doesn’t mean much unless they are worn down to the cords. Race tires should be stored inside and away from direct sunlight in a temperature controlled environment. If your tires have been properly stored, I don’t think they are too old. As to how long they last, I can tell you that when I first started out, I would get about 10-15 hours out of them. I was appalled to get such little life out of a tire. Later, when I got better as a driver, they would only last about 2 hours. After that, they really weren’t competitive. If you wanted to, you could blow through a set in about 30 minutes.

Hank

KOAN

YIKES!