Judging by comments from the BMW community at large this seems to be a common issue. My 18 plate Grand Coupe xDrive has 19" wheels with of course run-flats (but not M Sport suspension). Wheels are 8.5J rear, 8J front with 255/35/19, 225/40/19 Pirelli P Zeros respectively. Road holding is great but ride quality/road noise is not. It would seem changing to non run flats of the same size would produce little improvement due to the low aspect ratios. Cheapest option could be keeping 19"s but with deeper aspect ratios but would the increased rolling radius have an adverse effect on ABS, DSC etc? My thoughts are to source suitably sized 18" wheels with Continental All Seasons (non run flats) & offset the cost by selling the 19"s with the almost new Pirellis. I have a spare wheel kit on order in any case being of an age where not having a spare wheel is inconceivable! I did buy the car knowing there would be an issue with the run flats/wheel size having experienced shaken fillings on a previous Audi A5 Coupe with 19" wheels! The car otherwise met the right spec/colour/price making resolving the wheels issue worthwhile. I would be grateful of others views/solutions
