Along with my timing belt, water pump, 80k service, and several other maintenance items, I had Bilstein PSS-9s installed on my S4 this past week. I had purchased them from AWE as part of their holiday sale this past December.

The PSS-9s coilovers are height-adjustable and damping adjustable. According to X-1 Racer, the spring rates are 515 in the front (linear) and 443 in the rear (progressive). The adjustor knobs allow you to tweak the rebound *and* compression together, from a "1" (super aggressive) to a "9" (soft-ish).

I went with the Bilsteins because I was impressed with the ability to adjust the damping and wanted something that could work on the track. From my novice perspective, choosing a suspension for this car is like reaching blindly into a box of chocolates: <Forest Gump>you never know what you're going to get</Forest Gump>. I liked the idea of being able to adjust the car's ride quality and performance to suit my tastes without having to get seat time in every type of suspension or otherwise evaluating them based on written descriptions.

So despite some cons (small S4 user base, questionable use of rear progressive springs) I decided to take a chance with the PSS-9s; they're widely-respected as solutions for other cars and my mechanic was enthusiastic about them after putting them on Porsches.

I've uploaded a few pictures of the coilovers on the car to my public Fotki gallery. Check this gallery for pics of the suspension prior to installation.




Setup, Impressions

My mechanic set the ride height to 25 1/2" all around and set the PSS-9's dampers to a "4". After getting the car aligned, I toyed around with the adjustor knobs. Both the front and rear can be adjusted with everything still on the car, but it's not as easy as I would have hoped. The fronts can be reached by just turning the wheel, but I think the location of the rears require the wheel to come off. krazylegs says it's possible to get the rear adjustors by reaching past the wheels, but that's a nearly impossible squeeze and grab for me.

Edit: Yep, it's possible. Lying flat on the ground, the rears can be reached with some effort.

Below is a picture of the rear with the wheel off. The knob faces inwards at the bottom of the suspension.



With the dampers at "4", I've driven the car around for a few more days and a couple hundred miles, through my regular commute and around some back roads. As expected, the ride is much firmer than stock, body roll is tighter, and turn-in is much more responsive. There's still a bit of play left on sharp turn-ins or during lane changes at speed, so car is by no means as tightly wound as could it be. I was very surprised to see the ESP coming on much sooner than it previously did in my favorite turns. I'm not enough of an expert to comment absolutely on what's provoking it, but I do think the car's tendency to understeer has been greatly reduced and the rear seems to want to step out more.

When I have more time, I plan to experiment with the damping settings on the street and perhaps add a rear swaybar. I may also get some Tracksport owners here in Altanta to drive my car to experience the differences firsthand. Later this year, I hope to attend ACNA driver's events at Road Atlanta, VIR, and Barber. I'm very excited to see how the car handles these track events.



Additional Reading

AWE's Bilstein PSS-9 Product Listing

X-1 Racer's first impressions

X-1 Racer's second impressions

krazylegs installation comments and impressions

2008 Track days: Mid-Ohio, VIR, Barber