Chris Y, The threads you are reffering to at the top of the suspension are for adjustable coliovers, just because the X73 doesnt have those only means its not an adjustable suspension, the X73 is a coilover setup.

 

JASCLASS, thanks for clearing that up.

What is the definition of a coilover suspension? I've always thought of them as an height adjustable suspension system.

TIA!

 

Before my present 996TT (Standart german M030 suspension ??) I had a C4 with Porsche Sports suspension, which I believe was the X73. I do not find evident differences nor in the way it looks, nor in the way it handles.... in good roads.
In not so good roads, ( which abound in Spain) the M030, at least it's present setup in the TT, is by far much, much more confortable !! I have not been able to compare in a circuit. In real life , as I can not use both, I will keep with the M030.

 

For the 996 TT/GT2 variant, Porsche has 4 suspension variations.
In order of highest to lowest ride height:

1. USA Turbo
2. European (ROW) Turbo (M030)
3. X73
4. GT2

Each of these suspension setups is non-adjustable for ride height. Although I am not 100% sure about the spring rates, it makes sense that with each lower suspension the spring rates should increase to resist bottoming of the suspension. Therefore, GT2 would be the stiffest, folowed by the X73, the M030 and finally the USA Turbo setups.
I am told the GT2 rear suspension is retrofittable to the Turbo however the GT2 front suspension is not due to the presence of the TT's front driveshafts. Because of this, in order to achieve similar suspension performance as the GT2, people have opted to go to full coilover setups such as the PSS-9 variants as well as the H&R and others. In the industry, the word "coilover' applies to those suspensions that have a threaded shock body that the spring perch is supported on. The spring perch can be raised or lowered as required to achieve the desired ride height.
My philosophy with my suspension upgrade was to achieve the GT2 ride characteristics. I therefore had to go to a coilover setup and I had the ride height (measured to the suspension points from a flat work surface) and alignment set to GT2 specs.
One would hope the front coilover springs (Bilstein, RUF, FVD, H&R, etc.) used in the TT application are slightly stiffer than those of the GT2 since they are supporting the additional weight of the front differential, half shafts and related 4wd componentry. I have not verified this since the companies are very secretive with their spring rates (spring constants=spring rates=force required to compress the spring a certain amount).
Hope this sheds some light on this subject.

 

Thanks for the write up Ken...

I'm still not clear...JASCLASS claims the X73 is a coilover setup... But without a threaded shock body to adjust the spring perch, how can it be classified as a "coilover suspension." That's the part I'm not clear about...

Thanks in advance!!!

 

Chris,
It is just a confusion of terminology. The stock setups, as mentioned above, all have coils that physically surround the the shock body with the distinction that they all have a FIXED spring perch. Here is a photo of the X73:



A coilover, in the true definition of the word, has an ADJUSTABLE spring perch by virtue of the threaded shock body. Here is a photo of the PSS-9's and H&R's as examples:





One other comment. Upon looking at the different setups in these three pictures, it is clear that the X73 uses a slightly progressive spring set (spring stiffness gets stiffer with added compression), the PSS-9's are non-progressive and the H&R's are progressive.