I'm mid process upgrading my suspension (T-bars, shocks, etc).
The shocks I'm using (re-valved Bilstein HD's) have both bump stops and a spacer. A quick search on the spacer led me down a brief rabbit hole in an attempt to understand the purpose of the spacer. Most search results flat out said to toss it, some even said it was just packing material. It is not packing material, but rather an important design element to prevent you from internally bottoming out your shock, which is bad. Several other threads mention that depending on your ride height you should cut it down in size, eliminate it or trim a ring off the bump stop.
I imagine some of the confusion comes from a change in the provided bump stop. At some point in the past the provided bump stop was one piece, about the same length as the current bump stop/spacer combo.
My car will end up just below Euro height, 25.5" f / 25.0" r. Should I eliminate or trim the bump stop/spacer?
I had some time to kill (procrastinating actual work) and decided to model the shock at different positions. The standard Bilstein HD has ~ 7-3/8" total travel and at my ride height about half the travel has been compressed.
I'm glad I drew it up, visualizing the parts helps me understand the relationships. I 'think' ride height actually has nothing to do with whether or not to trim the bump stops. It looks like Bilstein designed this assy so that the bump stop would have to compress to about 1/2" before internal shock components crashed into each other, add some safety margin and it's realistic that this was designed for the bump stop to compress to ~1" WITH the spacer. Ride height has nothing to do with this.
If you run you car much lower than stock and are likely running out of compression travel in your shocks, trimming your bump stops just makes it easier to internally damage your shock. The solution is to have the shock body and shaft shortened.
Sound correct? Or have I turned left when I should have turned right?