Steve in SLO

Hi all,
After having new Bridgestone S-03's installed on the rear of my C2S, I have noticed a marked increase in rear end instability. The rear of the car seems to sway back and forth quite a bit and needs contant steering corrections to maintain a straight line. I tried holding the steering wheel still while going about 65mph and the yaw got ever-larger, so this is an inherent instability in the current set-up.
My car has PSS-9 kit with rear monoballs and RS bars.
My mechanic thinks this is just that the tires haven't been scrubbed on yet, and that realignmment would be pointless at this time. My worry is that the car is not stable until it is fully set into a corner, so it's a bit sketchy to drive hard.
We have dialed out as much neg camber as this setup allows. The mech says the kinematic toe was set properly last alignment (about 8 months ago on old tires).
Any ideas?
TIA,
Steve

Phil

New tires do have to be "broken" in a bit.

What tire pressure do you have in the rear?

Steve in SLO

Phil,
The tires have about 1K mi on them now, so they should be a bit broken in. I usually run 36-38 lbs, and have tried 35-40 with these, with little difference in the wandering.
Steve

Phil

in a recent thread
Greg Fishman recomened 32/34
Robert H recomened 33/36

John H

Sounds like my car when one of the nuts on a bolt on the right rear suspension loosened up. It's the one with the eccentric "washer type" bolt head. Sorry I don't know what it adjusts but it is visible when laying on the ground behind the car with the engine tray removed. The car was a handful and seemed to catch every groove in the road. I found it getting ready for a DE and got an emergency alignment at the dealer (yikes!)

Viken

This is perfectly normal when there is a drastic difference between the tread depths front and rear. Especially, when you get into tires with such deep treads. Also, you may want to lower your pressures if you haven't done so already.

GrantG

SO3's are very squirrely when new, takes a long time to break in...

ca993twin

See if you can "borrow" wheels/tires from another wide body (Q45 lives right around you), and use that to help diagnose if its your tires or something else that needs serious attention.

fluid15

Are the fronts also S03's?

993Widebody

I recently put on SO3s on all four corners and didn't notice any instability. I drove them hard on the track with less then 500 miles and was actually impressed with the level of grip and feel to these tires. Prior to the S03s I had P-Zero Assimetricos and I have a hard time saying which one is better as they were both very good street tires for the track.

I should mention, I have S03 Pole Positions, don't know if that makes a difference or even if there are non-Pole Position SO3s.

As far as Viken's point, I don't know that I agree. Although I hold his opinion in high regard, I had older, well-used P-Zero Assimetricos on the front when I put on new rear p-zeros. and again the car felt great.

Anyway, these are my findings. I generally run 36 lbs in the rear and 32 in the fronts (cold).

Steve in SLO

Phil/Viken,
I may try dropping the pressures a bit on both ends to see if it helps. Viken may have something, since the fronts are getting a bit long in the tooth.
John: I had thought about the eccentrics, but they're tight.
Grant: I know my last set seemed to take a long time to break in, but this time it seems worse...
Steve (OFE): I have a spare set of wheels...good idea about the changeover
Fluid15: Yes, the fronts are also SO-3s

Thanks to all...lots of good ideas...I will post when I have found a cure.
Steve

Viken

Yes, it is a combination of tread depth differences and the fact that the rubber compound has changed between new and used. This is why I change all four tires every time I need rears. You can always find a buyer for the half worn fronts. And, what's all this about tires needing 500 to 1000 miles of break-in? Slide them around for ten minutes and they're ready to go.

Greg Fishman

Steve,
You need to listen to Viken. He is right and you will be best served with new front tires. That will be the cure.

hn

Finally, somebody brings it up. I always wonder about this theory too. I don't drive my car that hard but I can see how frustrating not being able to drive the car freely during the first 500-1000 miles. Anyone has any info on tire manufactuers' recommendations on break in mileage?

thx

Steve in SLO

Alright, Viken,
I learned several years ago that you're 99% right 99% of the time. I think I'll get off some more $$ and buy some new front tires.
FWIW, I drive my car hard and am sure the tires are well past scrubbing in time.
I also just checked my pressures cold with my digital gauge: 30F, 32R--funny that my digital reads 3# lower than my analog. Now I guess I need a 3rd gauge as a 'tie-breaker'.
Steve