Kopierat från bimmerforums;
With 4 wheel air suspension, you just need lowering links to adjust the ride height. Pretty cheap or an easy part to make yourself.
It tells the sensors the car is riding higher than it really is so the car system will lower itself. Use adjustable links and you can set the ride height exactly as you want and the vehicles vaiable height system will still be functional.
There was a system available that bypassed the speed sensors on the adjustable ride height system on the car so you could set "LOW" and then drive like that without it reverting to normal over 15 mph but at $900 a pop, I dont think it was selling in huge numbers.
The löwer class.