As a few of you know, I just recently purchased my 2003 996tt. I've been noticing some very odd behavior over bumps. The car feels very bouncy/floaty/unsettled over any bumps, especially through turns. I know what a car (and a Porsche) is supposed to feel like, and this is exhibiting some seriously disconcerting behavior. I wouldn't describe it as bump steer, per se, but just very floaty and wants to step out (laterally) if there are any imperfections through a turn. It doesn't even need to be a huge pot hole... just a minor bump in the pavement. It's far less composed over bumps than any other car I've ever driven.

Could this possibly be the result of blown shocks? The PSS9s were put on the car 20k miles ago.

 

You might need to adjust the rebound on them.

 

I had PSS9's before upgrading and I felt the same thing. I think it may be related to the soft springs that come with the PSS system. This might also be related to the fact that you cannot adjust the compression on PSS shocks, only rebound.

 

Sounds like normal PSS9 behavior.

Seriously, you have two, no three options:
1. Tighten the shock settings (mainly front is where the problem lies) to no more than three clicks away from max hard setting. (it will suffer you a really poor ride as the compression follows with and the PSS9 are useless at swallowing bumps, but at least you'll have the car under control).

2. Send the shocks for revalving and make sure you get setting which are nowhere near PSS9 original settings - you need a lot firmer rebound vs compression damping to get a well controlled car with still some ability to swallow bumps.

Not affiliated with any of the companies.

 

MrWhite knows way more about this stuff than I.

MrWhite, did you put the Carbonetics LSD in your new ride yet?

 

Happening as we speak

 

Make sure your ride height is not set below bilsteins recommended / required PSS9 setting. Bilstein specifically spells this out in their installation instructions but many people set it bellow this for the "looks". If you are set bellow this height you will have these exact issues as the shocks will have very limited travel and you will be bouncing off of the bumpstops.

 

I'm going to verify the shock settings in front, and try Mr. White's recommendation of 3 clicks from max hard.

 

They are valved at "medium" right now. I'm about to go set them to full hard just to see the result.

I'm seriously considering ditching these PSS9s for something better.

P.S. What's my third option?

The car is set at 25.3 inches in the front and 25.5 inches in the rear. I know that I'm not bouncing off the bumpstops.

To be honest, I thought this was a product of the PSS9s right from the get-go. I had read so many GREAT things about the PSS9s on this forum (and others), however, that I was hesitant about questioning the end-all-be-all of shock/spring setups. Is this REALLY what the PSS9s feel like? I guess the vast majority of customers don't ever push their car to the limit...

 

I had the same problem. The car was set REALLY low (the helper springs were removed to get the car lower). I put in new helper springs and raised the height up to 26.5" front and rear )I think the rear is at 26.75") and for highway cruising, i set the setting at one click above full soft. It helps A LOT and makes the ride almost normal. For autocross (haven't tracked the car yet), i bring them up to 8 front and 8 rear (I have PSS10's where the higher the number the stiffer it is).

 

that on PSS9's 1 is the firmest and 9 is the softest. So I assume you are recommending trying 3 or 4 (on the firm side) ?

Thanks.

 

I've not tuned cars with PSS9/10 shocks but I have set up a lot of roadracing motorcycles and tuned Ohlins and other high performance shocks.

It's important that you have the dampening rates matched to your springs. Too floaty most likely means the shock preload is too light, like the spring rates are too soft and you're getting too much body roll in the turns. This coupled with not enough dampening. Loose feeling, out of control.

Stiffen up the preload if possible where body lean and roll are minimized but the tires will follow irregularities rather than skip over them. Then play with the dampening adjustments. Too much dampening and the ride will be rough and kick back on bumps too little and it will be like springing without shock absorbing.

You may need help from a race shop. GL

 

Are you sure you're nor over lowered and bonucing off the bump stops? My car felt a LOT more stable after I raised it about 1/2" in front and 1" in rear. It's still lowered, just not slammed.

Alignment makes a big difference as well.

 

If you are at 25.3" front and 25.5" rear that you are most likely too low for the PSS9s. This is just about GT2 ride height. All you need to do is jack up the car, take the wheels off and verify if you are set at the prescribed height as per the PSS9 installation instructions. Measure the distance from the top of the spring seat to the center of the shock mounting screw (minimum distance in the front is 75mm and the rear is 205mm).

The PSS9/10 coilovers have a specific ride height they need to be set up at for the shocks to function properly and avoid hitting the bumpstops. Per the PSS9/10 bilstein installation instructions, there is only a 10mm (20mm for PSS9) variance of ride height adjustment in the front, 5mm in the rear. If you are too low (i.e. GT2 height) and are on or near the bumpstops, you WILL have issues.

The following is an excerpt from page 7 of the PSS10 mounting instructions published by Bilstein and available on their US website. PSS9 instructions are identical except for the part numbers and the fact that the front setting range is 20mm (75mm-95mm). The same information is also contained in the PSS10 TUV certificate:

"The adjustment range of the spring plates is only approved within the range of the values given in the table below. Adjustments must be set so that the body is level when the vehicle is empty apart from the driver. The LOWEST approved adjustment and the permissible adjustment range are to be entered, stating the fixed axle reference points. (Example, see below).

Manufacturer PORSCHE
ABE-/ EG- BE- No. e13*98/14*0059*..
type designation 996 Turbo (4WD)
model 996 Turbo

FRONT according to permissible axle load and adjusting dimensions
spring part number
main spring E4-FD1-Y623A00
helper spring E4-FD1-Z349A00
shock absorber part number with damping force adjustment VM3-E716

permissible adjustment range
maximum permissible axle load 825 kg (1815 lb)
80 – 90 mm* = 10 mm range
* measurement:
top edge of spring seat down to the center of mounting screw

REAR according to permissible axle load and adjusting dimensions
spring part number main spring E4-FD1-Y518A00
helper spring E4-FD1-Y504A01
shock absorber part number with damping force adjustment BM5-D541

permissible adjustment range
maximum permissible axle load 1250 kg (2750 lb)
205 - 210 mm* = 5 mm range
* measurement:
top edge of spring seat down to the center of mounting screw

�� There are no technical objections against the use of all O.E. wheel/tire combinations.
�� The ground clearance in unladen state is reduced by the installation of special springs. It is the approximate equivalent of that of a partially laden stock vehicle. When the vehicle is loaded to the permissible axle loads the ground clearance does not change as compared to the stock vehicle. If spoilers, rear aprons and special exhaust systems are mounted, however, the reduced angle of slope must be noted (travelling on ramps etc.).
�� The specified minimum height of the coupling ball above the road surface with the permissible total weight of the vehicle (acc. DIN 74058) is 350 mm."


I think this makes it clear why some people that drive the car hard encounter problems if they have the suspension height set up at a height other that what is spelled out by Bilstein. Am I the only one that has read this document as it seems to put this "handling mystery" to bed? It seems clear to me now that if you want your PSS9/10s to perform properly on the 996tt, you must mount it at the specific ride height at described in the installation instructions with a 10mm variance in the front (20mm for PSS9) and 5mm variance in the rear. BTW, 10mm is only .39 inches and 5mm is only .195 inches, so clearly the PSS9/10 kit does not give you very much leeway as to where to set the ride height if you want the suspension to perform properly.....

Hope this helps. If I were you, I'd first check and see if you are set up per the above ride height requirements before you start throwing thousands of dollars at parts that in your case probably won't make any difference.

 

Just to add to John's helpful post - the range on the front of PSS9's is 75mm - 95mm.