Quote:
Originally Posted by FaRKle!
Are you guys sure it's not because of too much rebound? When the rebound is too high it'll pull you into the bump stop and keep you there, and then it's the bump stop that's bouncing you up. BMW dampers typically have a good amount of rebound bias.
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I guess we need to make sure we're all on the same page as far as description.
Damping (not dampening, that's what you do with a wet cloth) - The control of motion (via the shock).
So when you say rebound is too high (as in motion?) - do you mean that it's too soft so it rebounds too quickly?
Or do you mean it's too stiff (as in the setting is too high) and the rebound is slow?
I feel that there needs to be more rebound damping (slowing the extension of the shock). Presently the rebound is too fast and it's allowing the suspension to extend too quickly so the car feels jumpy. The rebound action needs to be slowed down.
Slowing down the compression damping a tad will also help as right now it feels like the suspension blows through the travel and (as you've stated) lets the car get to the bump stop and then there's no wheel travel left to deal with undulations of the track. That "packs" the suspension up and it can't do anything anymore. Too much damping on compression will also cause "packing" as the shock can't respond quickly enough so it acts like it's on a bump stop.
The car needs better rear damping control - more rebound resistance, a slight increase in compression and I think it needs to get away from progressive rate springs. They get stiffer more quickly and the valving in the shock needs to be able to do the same (shaft speed control). As you get to the limits of extension or compression you start taxing the limits of the damping control with progressive rate springs.
Just for background on my suspicion of what's needed, I have about 25 years of suspension tuning under my belt in the off road world. I'm used to controlling 20+ inches of travel with (generally) three zones of damping in compression and two in rebound along with playing with spring rates, cross over points of the springs and such. Lots of time (43 years) on motocross bikes too.
Present project - can't wait to start suspension tuning on this..
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