http://www.ridefox.com/fox_tech_cent...ning_Tips.html
Symptoms: Bottoms out, soft throughout travel
- Cause: Spring rate too low throughout travel or too little compression damping
- Solution: Use more air pressure or stiffer coils springs; increase compression damping
Any other resource will tell you the same thing. Added compression damping increases the resistance to spring compression, which may ultimately prevent bottom out. If it doesn't cure it, it will certainly help the condition. Couple that with proper length bump stops, and that may very well be all we need.
Bilstein HDs are notorious for lots of compression damping (especially vs. the likes of Konis). It's a reason who some people love them, and some people hate them.
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'02 S54 M3 (500/500 GC/Koni)
'08 N54 135 (JB4, DCI, BMW PS/Bilstein B6s, H&R M3 FSB, Strongflex FCABs)
'14 N55 X1 (JB4, BMS DP, BMS Intake, Alpina TCU reflash, H&R Sports, Bilstein B6s, E93 M3 RSB, Strongflex FCABs, baby seat)
'08 N54 535xi touring (Bilstein B6s, Downpipes, MHD tune, baby seat)