My A3 Sportback Sport has got to 16k miles and needs new front tyres, both have worn evenly if not a bit more down the middle suggesting tyre pressure could be a bit lower in future. I am happy with that. BUT the rear tyres, I have discovered, have worn badly on the outer edges (1.6mm outer edge 5mm inner edge) which I am extremely unhappy about. I have had the tracking checked and all is OK, Mr Audi says this is normal, I am thinking half my rear tyre life has been wasted. The car is running on standard factory suspension, wheels etc Any thoughts on this problem??