> I don't think the X5 still uses BMW's old flat tire monitoring system of tracking changes in rolling circumference.

Everything I have seen, including the owner's manual, says it is a direct pressure measurement system now in the U.S. Perhaps in other countries they still use the cheaper circumferencediferential montitoring system.

I believe it is now a legal requirment in the U.S., and that the old indirect systems do not meet the performance standards, e.g., if all four tires deflate an equal amount, current indirect systems will not detect it. NHTSA requires vehicles to be equipped with a system which can detect such uniform loss of pressure.

http://www.xoutpost.com/tire-wheel-br...-info-fyi.html