If you don't rotate the tyres is there a general wear pattern for the X3. i.e. back tyres go first after xxxx miles, then front after xxxx miles.
On my previous car (Hyundai Santa Fe), the car is normally front wheel drive and switches to 4 x 4 if there is slippage. Hence the front tyres get the most hammer. I normally try to change car every 2 years, so I managed at 15k miles to swap the front tyres with the back, and therefore didn't buy any tyres over 22k miles of ownership.
I'm thinking that I'm not going to be as lucky with the X3. Should I budget for 4 new tyres over the estimated 22k miles?