I've found the BMW is quite a tricky beast to get setup right and it can be very difficult when it's not right for a particular track. I'm changing springs almost every day now based on data, it takes me ten minutes and gives way better results than fiddling with the other knobs which are basically determined by the right spring anyhow.
Jerez in particular is a track where you should try hard to keep it as soft as possible for the flowing corners with just enough support for corner one so I dont think you should go stiffer springs than that at Jerez. You will probably find that those springs are just right for Donnington GP or Cadwell Park where you ideally need stiffer springs than places like Donnington National or Jerez. You're heavier than me but you're a bit slower so 10.25 should be plenty stiff enough, I would guess that you would even want less preload. Because you are talking about hesitating and not going into corners hard enough but at the same time saying you are bottoming out 10.25 springs with 11mm of preload I have warning bells that something is not clear with the measurements you have.
I dont have oil in the Mupo CSP but for me playing with the oil gap is something you do when you have the other parts reliably setup for the conditions and you want to fine tune the setup.
- Springs are 100% the first thing to change until you are getting close to full travel. Preload of 5-10mm is where I try to keep my window, outside of which I change springs.
- Once you have full travel fine tune the compression as needed
- Rebound adjusts according to the spring and preload to calm down or quicken the bike popping back up.
-Are you just using a cable tie to determine fork movement? I've been checking this method against my data and it's completely unreliable. The best way other than actual pot sensors is to put a camera on the bike looking at the forks. I know that suspension guys need something to work with but this and static measurements are near useless when you test them for accuracy against data.
-What happens with it mid turn since that is a different situation that might shed light on your geometry. One of my things to work on now is to look at the mid corner data to see how the bike attitude and compression changes and to tune it a bit with the preload. This is basically the dynamic side to what you are trying to achieve with static SAG and I think will be much more useful but more work to analyse.
