Get down low and look at any X5 from the rear. The rear squats down, which puts most of the load (i.e. wear) on the inside of the rear tires. The wider the tire the greater the difference between inside and outside. This wear difference is also increased when you carry a heavy load (or tow a trailer).

OTOH the fronts get most of their wear on the outside. This wear difference is increased if you do a lot of short radius turns on pretty rough surfaces (e.g. parking garage ramps, circular driveways, etc). It becomes even more noticeable when you always make short radius turns in only one direction (e.g. if you park on the top floor of a tall parking garage which has ramps that force you to always make sharp counter clockwise turns).

FWIW after seeing how much average tread was left when we had to replace our first set of tires on our 2001 X5, I began swapping tires front to rear every 5000 mi or so to even out this difference in wear. Yes I know BMW does not recommend this. But it works!

Funf Dreisig