One thing to keep in mind when selecting replacement tires for our HEAVY vehicle is the Maximum Load per tire. For the 20" tires on the M, the front and rear maximum load per tires are 2094 lbs. and 2337 lbs. I also read at Michelin that tires may be derated by the manufacturer when they are mounted on heavy SUV vehicles. See below:
* Passenger sizes used in Light Truck/SUV applications have reduced load capacity. This will differ from the maximum load branded on the tire sidewall.
The link below will take you to the TireRack web site with the full specifications for the factory supplied 20 and 21 inch tires:
http://www.tirerack.com/tires/tires....0&autoModel=X6 M&autoModClar=&tab=Specs
As hard as these cars can corner at high speeds, you do not want to risk a problem with tires that are not up to the capacity of the vehicle. Please read all the information before purchasing and mounting tires.