This, from a factory tech at Koni (yes, biased, but he describes why there is a difference):
"Bilsteins are harsh for several reasons but primarily the mono-tube high pressure gas design is always starting behind the 8-ball on ride quality to begin with and also BMWs are the single brand that is easiest to generate ride complaints on. We never make mono-tube street shocks for a BMW and we almost never get BMW ride complaints. Because the mono-tube already is at a ride quality disadvantage, Bilstein also has to compromise their valving choices and reduces so low speed damping.This tends to give you a trend that we have seen on a number of Bilstein applications in recent years that cars on their dampers tend to be not well controlled on low piston speed, subtle body motion and then over damped when the piston speeds get high. Add that to the mono-tube telegraphing more negative ride feel into the car and you have very common ride complaints. In some recent light truck and street car comparative testing, our R&D Manager commented that Bilstein lately has become "an easy mark" to improve ride and handling over."
Or in the words of Bob Tunnell at Bimmerhaus:
"Bilstein's bump damping is too harsh for normal street comfort."
That said, Bilsteins are a good choice for track and autocross applications.
Cheers. Gary
