I do rotate my wheels from front to back. I have 10.5 inch rims on all four.

Your uneven wear is due in part to the factory alignment of the rear wheels. You will notice that your wheels tilt in towards the vehicle. BMW set the suspension up this way to promote a bit of understeer which aids in the stability of the X5.

You can neutralize the rear camber (reduce the tilt). This will bring your wheels to more of an "upright" position. I have had my X5 set up this way for about a year now with no adverse effects on handling. I have been known to take an off ramp at a high rate of speed here or there with no problems. (We have no corners here in South Florida!!!)

JCL - How the hell did you go 45,000 miles on one set of tires??!! Wow!