Quote:
Originally Posted by cntzl
Believe it or not, my suspension was installed by one of the most reputable BMW shops in the Bay but the tech who did the install was new and wasn't really familiar with it. At the end, I just gave up and left everything as it came out of the box, meaning the spring perch is set to 40mm (same as the pic above) and my rear shock has the preload that came with it (the tech couldn't even break loose the nut on the shock body). What's interesting is that I have a friend who has the exact same car and coilover kit. I showed him this thread and he's just as surprised as me because his experience is the exact opposite. His car is even slightly lower than mine and he's running even stiffer settings (11-12 clicks in the rear) but he doesn't have any of this ride comfort issues that I'm experiencing. His was installed by the same shop by a different tech. This has been really frustrating for me to say the least...
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Maybe get the guys who installed your friends kit to look at your? or take some measurements off of his kit?
Assuming everything is in good working order wouldn't too much preload on the rear give a crappy bouncy ride since you need to overcome whatever preload force the spring is already exerting outwards before compressing it?
Ie at 190N/mm a preload of 40mm gives a preload force of 7600N or roughly 775KG. Assuming 1/4 the weight is on each rear wheel (say 400KG) and a spring motion ratio of 0.6 (then the "weight" on the spring is roughly 670KG ) the the spring is still pushing the car upwards with 100KG of force which needs to be overcome before the spring compresses due to any dynamic forces.
I imagine the numbers work out so you have some compression of the shock at rest but not much this means you have no or very little extension travel which would seem to make the car handle like crap over potholes. It also means bumps are not absorbed as the body will be lifted before the spring can be compressed further, again leading to a crappy ride.
The damper settings would not affect the ride much as they do not work unless the spring allows the suspension to move.
This is just my thought experiment and I have no real world experience setting up suspensions. A quick check would be to jack the car and see how much the suspension drops by. If it is less than your friends this might be the culprit no?
Can the experts tell me if I am way off?