Specs:

02 996 cab
PSS9's (I think they're 9/R and 7/F)
GT3 sways/AP drop links
19" CG wheels with Dunlop SP9000 (TP 36/44)

I have brand new rears and the fronts are in excellent shape.

It' been doing this for a while now, even before the install of the new rears.

Long story short, if you're traveling at 60 plus MPH and you swerve left and then immediately right (or vice versa), the car feels like it's squirming on the tires.

The best way to describe it is the car feels like it has truck tires with 12" sidewalls. It's only noticeable when you swerve one direction and then immediately swerve in the opposite direction (I discovered this issue when trying to avoid some debris on the highway). Very unstable during these maneuvers and it almost feels like the car wants to spin.

Vortex put it on the lift and couldn't find anything wrong with any of the suspension components. They suggested the first thing I should do would be to have it aligned. It has been almost three years since my last alignment (right after I had the Bilstein's installed).

I am bringing it in next week for the alignment as it probably needs one anyway. Can poor alignment really screw the handling up that bad?

Any other things we should look at? The Cayenne feels more stable than my 996 right now.

 

that should be an airtight suspension setup. The one thing that pops into mind is your front tires aren't properly inflated.
The two things I would try is air pressure and then adjusting that rear sway. If that doesn't help throw your stock sways on and try that (and if that corrects the problem sell me the front sway!!)

 

Tire pressures are generally what's recommended for that size. I use an aftermarket TPMS as well as a manual gauge to keep them properly inflated.

I assume you would lower the pressure?

 

Wow.....something doesn't sound right.

Mine feels like a go cart.

Did you check all the bushings?

 

Vortex did. They said everything looked perfect.

 

Could be tyre pressures. I run mine 32front/41rear Cold and 32front/37rear hot. The stock pressures have been known to make the front feel 'floaty' at speed and the back 'squirmy' on corners... my $0.02

 

those dunlop are japanese made, and is incompatible with your german automobile

in all seriousness they seem to be known for soft side wall, which could be causing the issue you are describing. Porsche recommands N rated tires for a reason, those side walls on N rates tires are freaking stiff.

here is a discussion in bimmerforums.
http://forums.bimmerforums.com/forum...ad.php?t=84208

 

Interesting. Could be the problem....

I hope it's just an alignment issue because my rears are brand new and the fronts have about 80% tread left. This will be my 3rd set of rears with the same fronts.

 

Yup...N rated tires....I thought it was not thatbig of a deal....UNTIL I bought a set of N rated to replace my Non N rated Contis and WOW...the handling difference was amazing....Sounds like the sidewalls to me....

 

my experience tells me that you have an alignment problem

 

Two approaches that you might consider in order to isolate root cause(s):

First, increase in tire pressure by 5~10 PSI and re-test to see if the resulting stiffer sidwalls makes any significant difference. Remimber that your contact patch will probably be reduced so be careful that you don't find out how to spin a porsche.

Second. Consider that transitional handling is higly influenced by shock absorbers. So try stiffing both f & r settings by 2 or 3 and retest. I run my own PSS9's much stiffer than noted in original post. Consider too that you might have a failing shock.

 

These are probably too soft for quick direction changes. You need quite a bit stiffer for the car to settle to neutral quicker. Also, what are your sway bar settings?
I assume your are you running 245/35 and 285/30 Dulops. These come with 10/32 tread when new. As these are all weather tires, you will probably get tire squirm with these tread depths.

You would typically like a short "pause" between left-right to let the weight transfer smoothly. The stiffer your setup, the shorter the pause will be, but less comfortable for daily driving. During evasive maneuvers you don't have the luxury of pausing. IMO, the car probably should feel unstable, like the rear end is moving too fast during the second half of the swerve. If you take your foot off the gas, it will only feel worse. Not sure there is anything you can do about it.

I hesitate to say it, but the car might actually be behaving correctly given your setup and the circumstances, and you might not recognize it. That is, it might be driving technique rather than the car setup. I don't recommend working on left-right swerving on public roads. Get to a track! In fact, understanding and interpreting vehicle dynamics at speed is something you can really appreciate after you experience it at speed. Get some 18" rims and cheapo tires and give it a go!

-td

 

the driver

 

9f/7r is way to soft... also check your sway bars... they might be set to soft as well... this is what happens when you start to track your car... you start noticing weaknesses.

 

I think you could increase the F psi to 36 cold.
Also, what speed rating are the Dunlops? What you describe can also come from using a lower speed rated tire than what is needed.