Eric,
The bump stops can be cut. Bilstein can do this as a special request by opening up the shock assembly (under high pressure) and you lose the warranty. Incidentally, all of the above was gathered through a very long in depth discussion with a Bilstein engineer. Cutting the bump stop will only give you a maximum of 15mm more travel. It will also eliminate any cushion from bottoming out, so you run the risk of internal shock damage.

By adding preload, you need to squeeze the spring by raising the lower spring perch. This will raise your ride height.

 

thanks ken,
perhaps bilstein will develope a slightly stiffer spring rate by 50-100 lbs and either open up their valving or using oil with less viscosity to reduce sag, either way from your explaination they will need to increase travel as this is a huge issue. as i would assume most buyers of bilsteins purchase them with the intent to lower the car dramatically. great write up once again.

 

Eric,
Your statement of as i would assume most buyers of bilsteins purchase them with the intent to lower the car dramatically. says it all.
The point of this writeup is not to bash PSS-9's because they ARE a good product. The point is to make clear they shouldn't be used as a means to an end, wherein the "end" is mistakingly thought to be a dramatic lowering of the car.
More aptly, they should be used to allow "some" height adjustability and damping adjustability as compared to the stock setup.

 

Increasing the spring rate will only exacerbate the situation... the proper fix for the PSS9 if you want to lower it beyond it's intended height is to shorten the shock body/shaft. That's the only way to gain travel back at a given height.

 

your right, but i was thinking from a production standpoint, using existing bodies and so forth. otherwise you need a piggyback or some exchange camber for the oil. which would inevitbly be an entirely different shock/ model #.

 

Good write up and good review for those that missed Ken's work last spring (that he was good enough to share at that time).
I had a file on all the heights because I was comparing Porshe's height profiles (rake) for each car (USTurbo,ROW,X73,GT3,GT2) for some work on my cars last spring.

I had the front of the US turbo OE as:
158 +-10
the GT2 at 113+-5.......which of course means it could be as low as 108.
I am successfully running at 108/109 with H&R components.
If I recall correctly, transposing the rear GT2 #s is problematic since it's a dif measure point (than the flat spot on the rear sub frame) we are accustomed to.

 

Gregg,
You are correct regarding the transposition of measurements to a turbo from a GT2. The disparity comes from the elimination of the rear suspension subframe rubber isolators to the body. This means the rear suspension subframe on the GT2 is closer to the body than in the turbo with the big fat rubber isolators. There are four of them and they are disc shaped. I can't recall the difference, but it was taken into account when I set up my car.

 

Ken,

How much travel do you have in your Motons? It seem that if you are lowering your car to GT2 height but retaining the 3-4 inches of shock travel (with a corresponding drop in the chassis of at least that much) that perhaps you might have brake ducts or other under car parts bottom out on the street.

I say this from personal experience, as I have the Ruf PSS9 system (set at GT2 height) on my car with tow hooks in the front that have bottomed out on certain areas of our local track. I would think this bottoming would be even worse if the shock travel were increased.

Paul

 

The only person I am curious to hear from on this topic Cary Eisenlohr.

I am convinced after much interviewing and research that for absolute performance, JRZ is the shock of choice.

But shocks are only a part of the story.

The thing I don't get is why people are so obsessed over ride height. Is it for the "look"?

Why is the GT2 ride height even the specific and primary factor in tuning your suspension? To me a suspension should be set up for what you want it to do and how you want it to behave and react at the limit. The ride height is what it is.

The GT2 and Turbo's suspensions are quite different in terms of components, pick up points, and geometry, and trying to simply transpose one ride height to another is too simplistic.

Arling's analysis is spot on, 70% of owners won't even know the difference, and making apples into oranges or vice versa is UTTERLY POINTLESS, unless you spend cjv's kind of money.

 

Tyson,
I can say I pretty much agree with you. I can only speak on behalf of my objectives. I decided to use the GT2 spec for three reasons in the following prioritized order:

1. Dropping the car to this ride height resulted in the control arms being nearly horizontal in attitude at rest. I wanted this so that the toe change was minimized with any translation of the suspension. For a given suspension compression or extension, a horizontal control arm will have the least impact on toe change as it scribes an arc about its pivot point, as compared to a sloping orientation such as 8:00 position for example. The slope of the scribed arc at 9:00 (level) is pure vertical.
2. Fully realizing that there are different components, pick-up points, geometry, etc, I still thought it made more sense to have "some" alignment spec rather than none at all. At the very least, it was a starting point from which I springboarded.
3. I admit, it looks better.

 

Caveat to previous post.....
The scribed arcs of the control arm and the steering tie rod should be parallel to avoid bump steer. To the best of my measurement techniques, they are darn close.

 

Well Ken, it also lowers the cg of the car a lot! Big benefit.


and yes ... it looks nice. I can't believe the bling king said that.

 

I put this in the other threads, but my master mechanic and I experimented with diff't ride heights beginning with GT-2, and knowing the bump stop distance for the PSS9s and the amount of travel. We came up with a final choice of 15 mm above Gt-2 specs b/c this lowers the car and still allows for reasonable travel above the bump stops. Lots of track time and mountain roads later, no suspension issues or handling problems. I am very satisfied with the PSS9s.

 

after 30K miles on my Pss9s.... I have no problems as well.

 

ken,

have you considered the location of your roll centers in relation to the tarmac at GT2 height?

-dave w