Here's why. BMW has a system on the 7's in place to sense a loss in tire pressure, and to display that problem as TIRE DEFECT in your Check Control. EVERY one of the 7's I've seen with the run flats has had problems with TIRE DEFECT coming up all the time because one tire is 1 psi different from the others. Fix it, and 2 weeks later you're back at the dealer getting the TIRE DEFECT message turned off. It's a pain.