I have a BMW 335i with 255/40 (rear) and 225/45 (front) run-flats. Both sets are original fit and have 23k miles on them. I still have 4mm plus on the rears and 5mm plus on fronts. I will change the rears before too long, but understood from your column a few weeks back that Bridgestone was introducing a more pliable range of run-flats to replace the existing 'hard ride' tyres which are supplied at present. Does this mean that in order to get a safe, uniform ride all round I'm going to have to change all four at once? Would be grateful for a steer (excuse the pun).