When I purchased my Z3 last November the dealer had put on two new rear tyres (255/35/18). Nice I thought until I dropped her from 5th to 3rd to get passed a truck, traction control kicked in on the flat on a nice sunny day (17.5 C). Thought I'd broken something! On closer inspection the rear tyres are budget tyres by the name of Sunny @ circa £70 a boot! Absolute rubbish but sadly have loads of tread left on them. You get what you pay for.