I have to admit I do not actually know the spring rates on the Ruf PSS-9 kit on my car...but wouldn't the rates be stamped on the springs as usual?? If so I can certainly look at mine and post the results.

 

I believe the spring rates for the various Euro versions (Ruf, FVD, etc.) of the PSS9's are the same, it is the shock valving that varies. Don't know whether the Euro. and US versions are different.

 

I don't think so, Bruce. Ruf uses different springs with their own part numbers and they look different. Here are pictures of a 996TT Ruf suspension kit. The numbers on the Ruf springs are part numbers and manufacturing dates, and not spring rates.

Sol

 

mo pics

 

last one

 

Perfpow: that's interesting, I'll check mine tonight. I remember Ruf telling me when they did my car that it was the shock valving that was different.

 

PerfPow: I checked my Ruf PSS9 suspension and your photo's and my springs have a Bilstein part# (R96 343 531 50) and Bilstein is printed on them, not Ruf. It's posible that the part # refers to the actual rates but I don't know. The Ruf tech. that did my engine/suspension conversion told me the shock valving was dictated by Ruf but the spring rates were stock.

 

Had a chance to stop by Perfect Power this morning... swapped some stories and tech talk with Sol. It has got to be one of the cleanest shops I've been in... definitely the cleanest shop bathroom by far!

Anyways, I can tell the shop runs like a tight ship... meticulous perfection abound. It's always nice to visit a real race shop... not knocking tuner shops at all, as comparing them is like comparing apples and oranges. They serve different purposes for the most part. Definitely looking forward to my cornerbalancing and alignment there.

I got some good feedback on what direction to take my spring rates from Sol. I then called up JIC, and their engineers felt that their 7/10 (front/rear:kg/mm) setup, while yielding a much more streetable ride, would more likely burn out the dampers if tracked regularly or at lenghts. So, that leaves me the following:

F/R
KG/mm, (lbs/in), F:R ratio
8/12, (451/677), 67%
9/12, (507/677), 75%
8/11, (451/620), 73%

I've currently got 12/16, (677/902), 75%, which is very neutral with very slight power-on oversteer.

Judging from the springs and F:R percentages, do you guys have an opinion as to a more optimal setup of the 3?

(I've got the 9kg/mm already, and may go with 9/12 unless somebody has other suggestions.)

Thanks,
Stephen
'01 Turbo Ti
455rwhp, 505rwtq

 

The USA Bilstein PSS9's should be 380 lb front and 660 lb rear. This spring rate includes the helper springs.

 

Thanks Todd, for our first data point! This is the kind of info we can use to digest suspension setups.

The ratio of PSS9 F/R is 57%, which is toward the relative end of the spectrum... the lower the number, the more on the understeer side as applicable to our cars. For instance, if the F/R is 100% (front and rear springs are the same), the car would understeer a lot more because the rear of the Porsche with more weight would maintained contact much better than the front, which is much lighter. I've included other ratios in an earliest post in this thread. I'm not saying this setup understeers, as there's lot's of other factors such as dampening rate, toe, etc... just saying that relatively speaking, there's a wider gap in this setup vs. others.

FYI for those of you interested: Helper springs don't come into play when figuring spring rates because they are fully compressed, which effectively means that their spring rate goes to infinite (equivelent to a solid with no give). So, the 380/660 spring rates when the car is settled on the ground is the same with or without the helper springs.

This is unless, of course, that the helper springs aren't fully compressed when car is resting on the ground (which I've not seen before, and shouldn't ever be the case). The reason for this is helper springs have very low rates to begin with relative to main springs. If they were actually to support any weight, once they fully compress during suspension travel, and the main springs start to come into play, you'd have a really bad transition point in your suspension travel that'd have very negative impact on handling. This can easily be exemplified with a suspension dyno. That is why you always see helper springs fully compressed when car's full weight is on the ground.

The job of the helper spring it to help the main spring maintain contact with its spring seat when the coilover is "stretched" out... case in point, when a car goes over a large hump.

And as the damper starts to bottom out against the bump stop, the graph of the spring rates will rise drastically towards infinity.

Stephen
'01 Turbo Ti Upsolute
455rwhp, 505rwtq

 

Stephen,
You are 100% correct here. Not that you needed to be told that anyway!! I went into this several months ago but I am glad it has come up again.
Here is a photo of the PSS-9 coilover on my car with the car at rest. It is very clear the helper spring rate is infinite as they are fully compressed. The helper springs can be fully compressed by hand as I have done it myself.



I am also very happy to see what you are doing here. I really hope we can collect as much spring rate info as possible. Regarding the USA PSS-9's, I would have to guess that the Euro PSS-9's and USA PSS-9's have the same spring rates. It was my understanding that only the top spring seats and helper/main spring collars were modified for the USA versions. That was done to prevent the noises heard from the springs binding during turning. Can anyone accurately substantiate this?

 

I recall a Panorama arcticle that had some interesting suspension, spring, shock data...

[URL=http://www.pca.org/panorama/sample_article_3.html[/URL]

 

Doug,
The link doesn't work.

 

http://www.pca.org/panorama/sample_article_3.html

 

Having tenders completely compress at ride height is not necessarily what you want. Tenders work with main springs not independently. In other words it’s not an ON/OFF switch during the transition; it’s actually a very smooth progression which is very easy to see on a spring compressor. If you are able to complete compress a real tender in your hands most likely you can bench press 600lbs too. The springs that you can compress in your hands are commonly known as helpers not tenders. Helpers are designed to keep the spring in the seats when in full droop. Most race cars running 1500 lb plus main springs don’t run the tenders in total bind at rest. Tenders are available in several different rates for this reason and have not only linier rates but progressive rates available as well.

Also don’t get too hung up on which cars have which springs rates unless all other variables are exactly the same. Shocks play a very big part in controlling springs, this why the rest of the world refers to them as what they really are, dampers. If you’ve seen pictures of that blue one off flared out RUF car from the car collector in Malibu, well that car came with PSS9’s and it was, in his opinion, undrivable for the street use. He came to me to put lighter springs in and when I told him they were not that aggressive we decided to put triple adjustable JRZ’s in and leave the springs. To this day he doesn’t believe I didn’t’ change the springs. He said the car is so much easier and smoother to drive they have to be different. The most amazing part of this is when I dyno’d the PSS9 the graph wasn’t that much different from the JRZ put the performance was.