Hi Guys,

I am on my second 996.3 GT3. The first one was always extremely stable at high speed but had a tendency to understeer in fast corners. Unfortunately we had an encounter with a significant puddle on the highway ending in me losing control, going into the brush and in the process flipping and totaling the car. After a couple of months waiting for my insurance to pay out, I went and bought myself exactly the same car again, because why change a winning team. After all everything was peachy until the last 30 seconds

Since I have had my new GT3, I have had it aligned twice (5000km's in total). This is because I am not happy with the way it drives at high speed. It corners beautifully but it is very twitchy and darty at high speeds. Up to 180kph it is unpleasant but manageable, but above this speed the car is downright scary.

I have read every alignment thread on Rennlist and other forums I could find. Naturally I have also looked at Roland Kussumaul's alignment spec's. However no one seems to talk about twitchiness unless their camber is over 3 degrees negative.

My current specs are:
Front axle:
Camber: -1º10'
Max camber difference, left/right: 0'
Toe total: +8' (left and right equal at 0°4')
Caster: 8°11' (left) 8°01' (right)
Max caster difference, left/right: 10'
Front height: 110mm
Swaybar – 1 from hard

Rear axle:
Toe total: 28’ (left and right equal at 0°14')
Max toe difference, left/right: 0'
Camber: -2°14'
Max camber difference, left/right: 5'
Rear height: 125mm
Swaybar – 1 from hard

A few things I have noticed:

• With the car in the air, the spring on the left front strut can freely move on the strut. I think there is a couple of millimeters play up and down
• The front wheels rub the front of the wheelwell lining at full lock (Left more the right)

I drive my car almost exclusively on the road i.e. autobahn, b-roads and mountain passes. I do only one or two track days per year. I am looking for a car that is stable in a straight line and I am happy to compromise on the way it cuts into a corner.

Please let me have your thoughts.

 

Alignment, ride height, tire pressure and road condition all impact this

Start with getting a new alignment base line, check all nuts and bolts while on rack and tire pressure

 

at first glance I was going to say Toe, but then realized its' in minutes and pretty much where it should be.

How old are the tires?

Any chance the toe links have worn bushings that could allow a little wondering of specs as you move down the road?

 

The tires were the first thing I replaced, so they are from last year with 5000km on them. I have Michelin PS4's on the car. Tire pressures are accroding to factory specs at 2.2 bar.

I also had the front coffin arms/toe links replaced with a new factory pair last year.

I am considering upgrading the suspension to the Öhlins R/T setup, but don't want to do it if there is an underlying issue I need to address first.

 

Try loosening the rear sway bar. Most run it full soft or one off full soft, even for hard track driving. One off full hard is very oversteery in an already very oversteery car. I run my front in the center or one notch from center towards full hard, Rear is one off full soft currently.

As said above toe often is the cause of "dartiness". Maybe check the rear toe links for wear.

It's normal for the coilover spring to be loose on the shaft when jacked up depending on the ride height and corner balance, unless you have helper springs installed (was never stock).

 

Are these stock GT3 wheels? If yes, are you sure?

I don't know about PS4s (I didn't think they had stock GT3 sizes), but what sizes are you running.

I guess another venue is having the car inspected for crash damage. Is it possible you might have missed something when you bought it?

Is the lip spoiler in place? Is the wing stock and set at the stock angle?

Were all the alignments at the same shop? Could they made repeated mistakes?

 

I am 100% sure I am running original factory wheels
the PS4's are available in the stock 996.2 GT3 sizes, it's the PS4 Sport that is only available from 19"
the factory original spoiler lip is installed
the wing is stock, but I don't know if is running the stock angle. I will check this
the last alignment was done by a very reputable Porsche racing outfit with state of the art alignment equipment. They are renowned for their chassis setup
100% sure the car has never had any form of an accident. All paint is original.

 

thanks, I will try softening the sway bar and check the rear bushes.

 

I prefer "0" toe. If your roads have any crown, toe and camber can make the car darty. Your camber is normal.

Do you have the original rear toe link? They can cause bump steer. Aftermarket toe links correct this.

I forget what the stock ride height is, but if the car is lowered, stock drop links can cause pre-load and can make the car respond in unusual ways.

 

If PS4s are available to fit the 996 GT3, that's awesome. I tried looking for fitment on Tirerack, but could not find them. They claim they don't make the OEM size.

Front stock size = 235/40ZR18 (95Y) XL
Rear stock size = 295/30ZR18 (98Y) XL

What sizes are you running?

 

Sorry OP, I've got nuthing others haven't discussed.

PS4's?
I too have never seen them available in 295-30 X 18
sigh

 

I don't know what the mileage is on your car is but:

The suspension settings (except the rear sway bar) look fine. Start with making there is no slop anywhere in the suspension, verify that the shocks are still good, check the rear diff while the rear is jacked up.

What kind of roads are we talking here: Smooth as glass, or rough? Is your car tramlining? Check your steering rack and the front tie rods...

Let us know what your find.

​​​​​​​Ray

 

Yes, I would like to know what size he is actually running. Everything else seems to check out for his car, but as unlikely a contributor the PS4s are, if everything else has been eliminated, then the unlikely is suspect.

 

Hi guys,

My apologies, I have given you the the wrong name for my tyres. I am running Michelin Pilot Sport N4's, I thought these were called PS4's but now I think these are still referred to as PS2's

Front: 235/40ZR18
Rear: 295/30ZR18

My car now has 80000km on the clock. The roads here in the Netherlands are smooth as glass. The B-roads are quite good as well. I think the car is tram-lining, but as this is a new experience for me, I can't say for certain that this is what I am experiencing. The best way to describe it is as a sudden left or right jolt. It is not that the car is unstable but unpredictable.

 

What do you have for shocks and springs? Are you CERTAIN that your tie rods are still good? Where is the car feeling twitchy - front or rear?