urquattro20Vt

Hey guys - I'm crossing posting this from teh 964T board as this forum is more active

Car is a '91 964 T with 18" Speedlines.

So today I went for a nice drive - 300+ miles - mix of curving two lanes, some highway, a few mountain passes...

But the car just didn't feel right.

It was unstable at speed. Uneven road surface would move the car around. When passing slow moving traffic and I had to pass over the road's crown - it would hesitate then as one side got over it would dart over too fast. I felt like I was all over the road.

At first I thought tire pressures were off - double checked and they were fine (36F/44R).
Then for a while I was thinking the alignment was off. But it brakes straight and accelerates straight. And it was fine a few weeks ago.

Then I got thinking about the tires. I just put new 285/35 Michelin Pilot Super Sports on the back - replacing a previous set (which I really liked). I took me awhile to figure this out - but the way the car was handling brought me back to when I first got the car and tried some Hankook tires. They were not good. At all. It was like the car was today (but worse with the Hankooks)

The first set of Michelins was awesome but with the new rears - something has changed.

What are people's experience running new rears with old fronts (Michelin Pilot SS's up front, too)?

There's no N rating to watch, right?

I'm wondering if the half used up fronts are "stiffer" with less tread compared to the new rears with full tread depth and it's throwing the balance off?

I thought it was common to replace rears and not fronts..?

Any thoughts appreciated.

Thanks

Brandon

LexVan

Mold release. Needs about 500 miles to scrub off. Why 44 in the rear? Try 40.

spartansix

I agree - your rear pressure seems a bit high.

urquattro20Vt

I appreciate the input.
The general consensus among the turbo guys is the turbo cars like 36/44. And I agree. That said if I'm putzing around town I'm ok with a little less - but for spirited mountain driving the car likes 36/44.

Regardless - pressure is a constant in this issue. I'm running same pressure as I've always run...

Thoughts/BTDT appreciated - thanks again

fasterlaster

Might be worth making a visual inspection to ensure you do not have any suspension bits loose.

Spyerx

Those are cold pressures? Way too high.
Maybe good for efficiency and tire wear, not good for traction.

kos11-12

It seams too heigh , You could start with 32/34 psi and increase by 2 psi at the time until it's become harsh and then back up,

urquattro20Vt

I'll try lower pressures - but again that's not the point here....air pressure has been held constant. Biggest variable is a new set of rear tires - same make/model as before -which matches the front. Michelin Pilot Super Sport. I thought you could replace just rears and keep old fronts - apparently not with Super Sports? Don't people do that with PS2s?

FormulaRX

Rear at 44 is too high. Is that cold pressure? Once the heat from the engine and turbo come out the sides it will drive up the pressure of those tires. I'd say 40 max is where you want to be. I'd go a tad lower at 38

-nick

I'm not familiar with the PSS tires. Have they released an updated version that you now have on the rear? How old are the fronts? New tires will always feel a little squirmy for the first ~200 miles but it sounds like you've passed that mark. I wouldn't blame your rear pressures, though 44 might be a tad high for that size on 18's. How was the wear pattern on the old rears?

Not that it would change with new tires, but when was the last alignment?

urquattro20Vt

Ok so closing the circle (pretty much) on this one. Got the new 225/40/18 Super Sports (fronts) mounted and the issues seem to be gone. I say "seem" only because I have not had a chance to get into the mountain twisties - but on a highway drive (where the issues also occurred before) the car handled like it's supposed to. Not darting with surface irregularities or inconsistent turning behavior.
If you are running Super Sports - based on my experience I'd say replace all 4 at the same time.

If I find the car isn't handling as it should next time I do a canyon run I'll update here.

Ohh and for the record tire pressure made no difference.