Jagbuff

Hi:

I have a question regarding steering feel on my 97 Cab. I am new to the car can still getting use to the steering but have a couple of questions for the list.

The steering feels very nervous and not confidence inspiring. The car has no history of damage and has less than 25K miles. All the suspension parts check out on inspection- there is no wear.

Here are the symptoms:
The car tramlines quite a bit on uneven surfaces and darts this is accentuated with speed - it is quite sensitive to wind changes (that in itself is not abnormal allthough makes for continuous steering adjustment which doesn't sound right for an Autobahn burner)

Under hard acceleration it will drift to the left and when I back off the throttle it will drift to the right.

It drives straight under slower acceleration and under braking the car tracks absolutely straight. It does not wander or feel weird when going though large depressions on the road.

I checked the tire pressures - one of the rear tires was at 25psi - and the darting got a little better but still far from a planted feel.

The PO very recently replaced one of the rear tires b/c a puncture. This would mean there is 7K miles between the two. As that significant that it would cause the change of direction under acceleration and the nervous feel.

Is an alignment in order?
TIA
Franck

Joe L

Hey Franck-

Is this your first? If so, welcome! I am by no means an expert, but here is some of my experience: Trammlining can be caused by the uneven tire wear - most people only get about 10k miles out of the rear tires, so a 7k mile difference could be significant. Also, if the toe on the rear end has recently been reset, check the bolts to make certain they are tight. A loose one could causes a wheel to wander, which would give you a very nervous feel (and is obviously dangerous). Lastly - these cars do have very sensitive steering. So if you are driving with a 'death grip' on the wheel, you could be causing the car to react to every little change (experience speaking). Try to relax your hands a bit - i.e. drive with a firm but relaxed grip. Oh yeah, and have fun, there really is no substitute!

ksimpson

Franck,

There are a few things that could be causing this.

- Tyre pressure as you pointed out, but you have already checked this.

- Wheel balance - worth checking and is an easy and relatively inexpensive fix.

- Wheel alignment - a bit more expensive, but it needs to be right on these cars for them to handle well.

- Shocks - a lot of discussion on Rennlist about shocks and how you tell if they're gone. Not always easy to tell, but they can cause all sorts of handling problems.

I'd go with an alignment and wheel balance first to see if that helps. If not, you may have to look closer and the differing milage on the rear tyres.

The

stephenc2s

As ksimpson said, try checking the tire pressures. I normally use 36 in the front and 44 in the rear.

TheOtherEric

What type and size tires do you have? For sure, 25psi is WAY too low (look at the sticker on the driver's door). But that's probably not the "problem." I've personally found Bridgestone S02's to tramline terribly with my setup (lowered with PSS9's and TRG sway bars). They are SUPERB on the track, but tramline unacceptably on the street with my setup. And it's also a function of alignment. You should probably get yours checked and maybe realigned (up to $400 at ONLY a qualified Porsche shop). You may want to post your alignment settings and re-ask the question. And what is your suspension?

mike cap

Franck,

I think Joe is on the right track. Actually 10k miles on rear tires would be very good results, 7k to 8k is probably more typical. Sounds like you are driving with one new and one worn-out tire on the rear.

Our cars are VERY sensitive to all things tire related. Pressures, uneven wear, cupping, etc. I would have all four of the tires looked at by an expert Porsche shop to see where you stand. Sounds like the PO may not have been "tire aware" (changing both rear tires at 7k would have been the correct course of action), so you should have your shop pay special attention to the condition of the fronts as well. Mileage? Age? Tire age, as well as mileage can affect their performance.

Of course, have the shop check alignment and make double sure there is not something loose, bent or broken in the steering or suspension.

Jagbuff

Thx for the suggestions. Here are a few additional data points.

The suspension is stock - no special option - and shocks are in good shape. I am running 35 psi on Pirelli P Zero (N1). The PO had a harzard insurance for all four tires so the rear one got replaced for free - that's why he didn't do both rear...it's transferable...maybe I should go driving around a construction site an see if I can get the other rear replaced!

I will try changing tire pressures to see if it makes any difference.
THX

Jeff96-993

I had a similar problem, and it was the rear tires. Turns out one was 1/2" larger in rolling circumference, and it caused the same effect you're feeling.

I replaced both rears, and the problem disappeared.

BS911

Ditto on the mismatched rears. I had a mismatch for a brief period of time due to a vandalized rear. Accelleration would push the rear one way, deccel would pull it back the other. Very unnerving. Went away completely with new matched rears.

TrackJunke

Definatley a tire issue. Get the other tire replaced.