750iL - rear suspension height after wheel change

After replacing 18" wiith standard 16", the rear end seems about 3"-4" higher and is very firm. Anybody's thoughts about this, did I need to do something else when I change the wheels or has something gone faulty and the wheel change was just coincidental.

assuming you used a 'standard' plus-2 wheel/tire combo, it sounds like you now have a coincidental self leveling problem. was anything else changed?