Like it has been said, toe is what wears the tires fast, so adjust as close to 0 as possible.

I often see techs check for loose ball joints at the rear of a air suspension X5. They jack the vehicle and find to play. The problem is that the air bag is pushing on the suspension arm and will make any play non detactable. The tension needs to be removed from the air bag or it must be deflated to be able to check the rear lower ball joint. May be that's your problem?

__________________