I had run flats on my curent car which is a 535d Sport, they were awful. I changed them for regular tyres as soon as I could. Luckily I had specced a spare wheel. Transformed the car.

My car is now 3 years old and having driven an E90 and several E70's I can tell you there is a massive difference because the tyre technology has improved and the suspension is now designed for run flats(it wasn't on my car).

My X5 is due in January and I wwill be sticking with them as I thought they were fine when I test drove the car and also because it is impossible to spec a spare wheel in the UK.