Originally Posted by Str8EJ
Bumpstops do not affect ride height. Springs determine ride height.
Cutting bumpstops allows for an additional inch or so of travel near the bottom of the damper's stroke. This is a benefit for lowered cars, since they have reduced shock travel lengths compared to stock. Cutting, or even omitting, bumpstops will not change how a car sits. Bumpstops prevent shocks from being damaged from being bottomed out. Bumpstops do not change the behavior of a suspension system. They are a rubber buffer to prevent metal to metal contact within the damper.
Yes of course we all know that. If you search you will find many people discovered to their dismay that when using lowering springs (or perches) with OEM or aftermarket "sport" shocks they were riding on the bump stops. Non-xi and xi. Someone posted that Eibach recommends trimming the stock stops, and many non-Xi people already use shorter e36M3 bump stops (front, Z4 rear) for this reason.
It is not yet clear if this is necessary on the Koni/eibach combo but it is not unusual in general that the stock bump stop is just too long when aftermarket pieces are used, and the suspension is actually riding around on the stops once car is down & off the jacks.
I would suggest anyone doing this themselves do some careful measuring beforehand to make sure this is not the case, and if it is to use appropriate length stops for the spring/shock combo being installed. I am planning to do the Koni/eibach later this summer and will be very interested in getting this right.