Well, yea but the F15 is still quite new. Search the net for the X5 E70 air suspension, I doubt there are many of them that did not have problems with this.
http://www.bimmerforums.com/forum/sh...suspension-sag
Lot of guys with problems, and I doubt they have have similar issues on their normal-springed front axels.
Sure, there are a few functional benefits from air suspensions. The car could have the front axle air damped aswell, since the compressor etc is already there. And the driver could have the option to raise or lower the whole car, but we dont have that either.
I also forgot to mention that this whole system requires an air dryer, to get the moist out or everything freezes inside. The filter inside the dryer needs to be replaced once it cannot contain more moist.
Lots of hassle for the small benefit of a self suspending rear...even pickup trucks get by without having the rear self-adjusted