Just noticed something I find a little odd, my car has done 17,000 miles, the rear tyres are just about on the wear bars, yet the fronts still have a little (1.5mm) of life left in them, now I always believed the quattro/haldex system mainly drove the front wheels, only supplying torque to the rear when required, so being as the front appears to have more work to do with weight, acceleration, steering and braking why are my rears worn more than my fronts?