Resurrecting this thread, as I have now had BMW performance springs (thanks UR25IO) with Bilstein B8 dampers installed by Advan last week. Over Christmas I also fitted whiteline inserts in the rear subframe bushes, using the excellent DIY elsewhere on this forum. Having now been for several drives, the changes are positive as long as the roads are mostly smooth-ish. The car feels tauter and rolls less, as was expected. My confidence on sweeping curves is higher, as it quickly adopts a set and points true. While I can induce some axle tramp & "skipping" over bumps if I try, it recovers sooner with far less of the TC flashing light effects from the dash than before.
Ride is overall better than I expected - more than acceptable on most roads around Sydney that I use regularly, even over speed humps. Roads with frequent patched sections or undulations induce a mild jiggling which could become annoying if those roads make up a large % of your driving. In any case, I have experienced no "crashiness" or bottoming, even over the worst bumps. Drop is around 20mm compared to the non M-sport suspension, which is close to what I sought. Curiously the RH front is about 6-7mm lower than the LHF, which I will monitor as I don't recall it being noticeably different before. I still have reasonable ground clearance, so it passes the driveway test without scraping the exhaust tips.
If cost was no issue, I would have gone with the complete BMW PS package and M3 suspension bits, but this was not something I could justify (to myself or to my better half).
Next step may be to install a bigger front sway bar … and of course replace the RFT's when they wear down, with regular tyres. In the meantime, I intend to rack up the km on my favourite driving roads.
