My 1998 A4 2.5 TDi Quattro Tip has a top speed of less than 130 mph and therefore according to a proprietary speed index chart - I could fit H rated tyres or even U at a push ! However, all web sites (and presumably Audi themselves) give a W rated tyre for this vehicle. That's 168mph and more than 40mph over what the car will do flat out, downhill and with a following wind ! Why the hell is it so high, is it something to do with the tyre construction needing to be suited to the quattro system ? If not, then as an engineer this value seems illogical to me and I would tend towards the logic that says the top speed capability of the tyre should adhered to but as this is only about 0.00001% of the the working life of the tyre the chosen speed rating should reflect the usual working speed of the tyre which is within the H rating or anything between H and W ?