09-25-2012, 03:34 PM
Location: San Luis Obispo
Join Date: Sep 2012
Mein Auto: 2000 e39 M5
Custom Bilstein PSS9 Coilovers
I just want to share about the new coilover setup for the beast and provide a description of the modification process. I bought my beast used, and the previous owner threw on Koni FSD, which were way too soft for my taste. She felt sluggish around corners, and it felt like I was either driving a boat or a SUV not a 70k super sedan. The ride would sway, dive, and bounce around even on the slightest dips. I decided to go with the Bilstein PSS9 coilover set up because Bilstein offers a revalving service at a reasonable price. The money I saved from going with the PSS9's instead of KW's V3 went into the revalving service. By doing this I was able to up the stiffness to whatever I wanted. I chose this route because of the recommendation from my mechanic at Precision Motorsports in San Luis Obispo, CA who specializes in race car preparation and he felt like the spring rate and valve stiffness from a majority of coilover kits were designed to appeal to the mass market and not necessarily to the true driving enthusiasts. We sent the shocks on over to Bilstein to up the stiffness. Stock PSS9 valve rates were (F)184/130 (open) and (F)300/175 (closed), the rear were 200/136 (open) and 312/200 (closed). The shocks were revalved to (F)321/151 (open) and (F) 1065/483 (closed), and the rear were stiffened to 335/148(open), and 868/461 (closed) (tested at 10"/sec speed). The springs that came with the kit were also replaced with H&R racing springs with a spring rate of 800lbs all around (front and rear).
Because I had the springs from the kit swapped out with shorter/smaller(diameter) springs (to save weight and increase stiffness) I needed additional hardware components in order to insure fitment. My mechanic fabricated and machined the necessary hats so that the springs could be mounted. Helper springs also had to be ordered from Bilstein to help the main spring stay in contact.
Here is a write up of how the project was performed:
Instructions to be used in conjunction with standard shock replacement instructions readily available online.
After front struts have been removed, reach up and hand remove BMW upper spring perch/ bearing assembly which will not be used in racing set - up.
Pre assemble your Bilstein PSS9 front struts with collar nut first [ lock nut is optional ] then helper spring, then divider collar, then main spring on top, then special hat with needle bearing [ optional for quieter steering ]
Now this assembly can be fitted to car just like you fit the stock set - up. For a first try at ride height set the front spring nut in the middle of Bilstein threads.
After rear shocks have been removed with perch attached,
use normal safety measures described by factory with spring compressors to remove spring and top hat. With a bench grinder you can grind down inner perch so that the main spring inside diameter clears the cone in the middle for a full metal to metal spring contact.
Now install flat washer to shock
Install adjuster nut [ locknut optional ] Slip helper spring on, then divider collar then main spring, then top hat and upper perch, torque center nut
the picture shows main spring below, either way is fine. Now install rear assembly into car, for initial ride height you can try adjusting the nut 40mm from top of the thread
The car is now extremely responsive to accelerating turning and minimal dive under braking, car is amazingly flat it corners now, much more stable in all conditions, huge increase in confidence entering curves, car feels much more planted, adjusting the shocks from mid position now will be the next step.
I'll admit I was quiet hesitant at first to go with such a stiff setup, and this type of setup may not be for everyone, but after installing it and driving around town even with the rears set to the 9 (highest stiffness) the car finally felt right...the way it was meant to be as she left had just left the factory. My beast is my daily driver, and the stiffness is not rough at all. She now handles like a new ride, and is screaming to be driven hard! Hats off to Franz at Precision Motorsport for going the extra mile to machine the necessary components and finding the right helper springs.
[Disclaimer] this is a racing modification for off road use only ! Next stop Buttonwillow Raceway Park !
Feel free to contact Franz Bluschke at Precision Motorsports if you are interested in learning more about a custom suspension setup.
racing at email@example.com or 805-423-5502