I've got a set of RUF PSS9s sitting at home in the box and I've been toying with the idea of putting them back on the car but wanted to make sure I set them at the correct height for optimum performance as designed. I've been doing some research on line due to all the talk of handling problems when the car is pushed hard due to the PSS9/10 being set too low (ex GT2 ride height). This was addressed by the lengthy post by KPV on this forum couple of years ago. The one thing I have found out is that the PSS10 mounting instruction are quite explicit in that the PSS10 coilovers only have a very narrow adjustment range for both the front (10mm) and the rear (5mm)!! I believe many people are fooled into thinking that you can adjust these things anywhere from stock height down to GT2 height when in fact that is completely false. Once you set the ride height outside of this narrow range as defined by Bilstein, you are essentially outside of the optimum operating envelope as designed by Bilstein - thus the handling issues.

The following is an excerpt from page 7 of the PSS10 mounting instructions published by Bilstein and available on their US website (I have not been able to acquire the PSS9 mounting instructions but they should be very similar. I called Bilstein and they said they will provide me a set) 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 is 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 know 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 and 5mm variance in the rear.

 

I've yet to install my 2nd hand fvd pss9's, and I read the same thing in my instructions (which I got from Bilstein). My only hope is that if the car is set up within the specified adjustment range, it will at least be a little bit lower than stock, since curing the 4x4 height of my car was one reason I opted for coilovers in the first place!

 

Post some pics of what the car looks like when set up at the recommended correct height. According to what the PSS10 installation instructions read, the car should sit a little lower on PSS9/10s than stock:

"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."

The way I interpret it is that the car sits a little lower than OEM due to the stiffer and shorter springs of the PSS9/10 but when loaded to the max permissible load, both the stock and PSS10 car will be at the same height. In other words, the OEM springs start out higher but compress more with load since they are softer.

Clearly, the PSS9/10 kit was never designed to lower the car much. It's a great set up to sharpen the car's handling but ONLY if set up at the required height as per Bilstein. The small 10mm front and 5mm rear variance is there to allow one to level and corner balance the car. I would be willing to bet that 90% of the people here bought the kit in order to lower the car and get the correct look while being completely unaware that the PSS9/10s do not give you the leeway to lower the car to where you want, quite contrary, the PSS10 instructions tell you exactly where the spring seat MUST be set at height wise with a tiny variance (until now, I certainly wasn't aware of it). When people set the car lower than the required setting, in doing so they end up riding on or near the bump stops since they are outside the proper functioning envelope of the shocks. Effectively, this is very similar to running lowering springs on OE shock where the shocks are also out of their optimal operating envelope. For normal driving with smooth roads the car does OK and looks good but when pushed hard or on a less than ideal road the suspension starts to hit the bumpstops and acts erratically and unstable. Since in 99% of the cases people don't really know what the car would handle like if set at the correct height where the shocks are designed to work, they are happy as the car looks "cool" and they think that's what it should handle like. "I just spent 4 grand on this suspension, it must be great!" Effectively though, most people pay a lot of money to get a great look and questionable handling.

My PSS9s were originally set at GT2 ride height and then removed because of bump steer and some instability when pushed hard at high speed. I currently have H&R coilovers set at GT2 height and the car is more stable at high speed compared to the PSS9s but still not where it should be in my opinion if the road is less than smooth. I dug up the TUV certificate for the H&Rs and just like the PSS9/10s, the H&Rs specify a height that the spring seat MUST be set up at during the install with a 10mm variance in the front and 10mm variance in the rear. I confirmed this with a call to H&R. When I get back in town I will put my car up on jacks and see where I am set up height wise. I am willing to bet that I'm lower that specified and thus the shocks are outside of their designed operating "sweet spot". It still amazes me how many shops mount the PSS9/10s, or other coilovers for that matter, with disregard to the height requirement spelled out in the installation manual.

The more I think about it, the X73 Porsche suspension is looking like the best option for lowering a 996tt correctly since it is a Porsche product specifically designed to work with the 996tt where the shocks are teamed to work optimally in their "sweet spot" at the lowered ride height of the matched springs (which lower the car 40mm front and 30mm rear compared to US OEM suspension). There is no chance of error during set up since the X73 is not height adjustable and thus prevents people from setting it at a height which is outside of the shock's CORRECT operating envelope. In summary, it seems to me that the PSS9/10s are a great product but ONLY if set up precisely as per Bilstein's instructions. Obviously if you are a hardcore track junkie you are running Moton's and such which are a whole different ball game.....

 

Thank you for the informative post, I suspect the same issue occurs with the 997 PSS10/Damptronics, this may explain the rash of drop link failures on excessive lowered 997s. Of course the damtronics also have electronic gremlins that can cause a terminal failure...nice.

 

The PSS10 for 997 tt has 20mm front and rear drop range. there for the car can be lowered 20mm without any problems according to Bilstain.

 

That's good to know, so Bilstein changed things for the 997.

 

Yes Doug, I'll try to post my positive experience with Bilstein over the weekend.

 

I'm no suspension expert but I think the rear height is very important. That's where all the weight is.

I've driven my car on street and track and find it pretty well dialed in. I did have the front raised 1/2" and found it to be less twitchy and "bouncy" as the front end doesn't bottom. It's much more controllable if you encounter an mid-corner bump since the suspension has the ability to soak it up.

Not sure how visible ride height is in my avatar, but you can see where it's set. There is a definite rake (the front is lower than the back).

Wondering if the stiffer springs in the FVD version will allow a bit more lowering?

For the record many other brands do allow you to lower car more while maintaining the required travel.

 

Judging by the picture in your avatar, your car definitely seems higher than GT2 ride height or most PSS9/10 cars you see on this forum. It seems like you have about 1" or so of space between the tire and the fender as opposed to flush as many are running here. You are probably at or very near the correct ride height for the PSS9/10 coilovers hence the handling improvement after you raised it.

 

For comparison sake, when your car is on level ground, do you know what you measure from the ground to the bottom of the fender both left and right on front and rear? I am assuming you are on 19s with 235/35 and 315/25s, right?

 

Guys on a similar note. Im looking to change my suspension for a more Road Compliant ride, i.e. softer and more bump absorbing. UK roads are nasty!! Which coilover of the ones mentioned would be best for this, also I would like it to be able to be readjusted for track days.

 

I have found the PSS10 to be relatively comfortable in regular use.
Almost like stock when the adjustments are on the "soft" side.

 

25.5" front and 26" rear running 235/315 combo on 19s.

Measuring from ground to top of fender opening.