I have had 3 BMW's with run flats and each of them I have fitted conventional tyres when the first set of rears have worn out. I think run flats are getting better, but conventional are way better even now.
The rears on my current 640D will need changing soon and I will be going for conventional Michelin pilot super sports as fitted to the Alpina B6 and M5. I will change all 4 even though only the rears are worn. I'll tell the insurance and have not had issues with BMW and warranty on previous cars.
