Here's the BMW company line:
Monty Roberts from BMW Product and Technology communications tells us that run flat tires are standard on most BMW models with the exception of some BMW M Models. He said specifically that run flat tires have several advantages and that they "Support BMW's EfficientDynamics Strategy by eliminating the extra weight of the spare tire, jack and tools in the vehicle for better balance, dynamic handling and fuel efficiency."
When asked about the criticism of run flat tires Roberts said "run flat tires by their design do have stiffer sidewalls than conventional tires, however, all current BMW models that use run flat tires have suspensions that were significantly developed for use with this technology." He added "These suspensions have been developed and tuned for the best possible ride comfort. The safety benefits of run flat tires are so significant as to outweigh any possible trade-offs."
When asked if owners could or should swap out their run flats either when a replacement tire is needed or because they're looking for added performance, Roberts was unequivocal. "We do not recommend replacing run flat tires with conventional tires," he said, "that deviates away from the original design, safety and suspension calibration technology that the run flats were originally designed for."
You know the famous "Why don't they eat a cake if they have no bread?" - that was for a longest time a default quote to signify "living in a bubble" and "detachment from reality". I think Mr Roberts needs to leave his usual bubble and visit the real world. In the real world, problems like closed tire stores on a Sunday of a Labor Day weekend happen quite often. Then people get sick of the BS and replace run-flat tires with regular tires since they have to lug around a spare anyway. Why not use the superior product at lower price when you have proven that run-flats without a spare are as useless as a bicycle is to the fish?
Ah, the spare tire and THE GENIUS of BMW engineering to not provide space for the spare tire ... See, I don't need spare tire if I drive in 50 mile radius from home - cell phone and a tow will do the job nicely and without a problem. Yes, if I cannot afford to spend $200 for a tow, I have no business driving a new BMW. Besides, just one set of tires without flat already offset the cost of the tow - and then some. And I'm on third set now, so ...
So, I do not need a spare for around town driving, that's established. But I do need it for a road trip, don't I? Now, BMW engineering geniuses, what else normal people take with them in the car when going on the road trip? No, not the slide rule, Hans ... they take luggage. You know? Thingy that holds your clothes, toiletries and weed? Yeah, that. Good. Now ... Do you have an idea where the said luggage is supposed to go? Werner, drop that stupid roof box design sketch and come back here! Where were we ? ... oh, yes, where to place the luggage in the car? ... anybody? No? OK, geniuses, the luggage is supposed to go THERE. That's what we call "trunk" and load it with luggage for road trip. Do you see what's in there? Ja, ze spare tire, correct. Soooo ... how am I going to fit the luggage in the trunk when a spare tire is there, geniuses? You know, the luggage that I need for a road trip?
Crickets ... after two years, still only crickets.
Seriously now, I travel a lot around this country and I lived in Europe for the first 34 years of my life. I get how Europeans (especially Germans) might see this as ideal solution. The problem is, when I think of long road trips I did all over Eastern US and possibility to do it in a BMW without a spare ... no, thank you. Even if rental company would offer to "upgrade" me to a BMW free of charge - Not. Going. To. Happen. Not without a spare tire, anyway.
Question for all those replacing their RFT's with conventional tires:
Are you also having your suspensions recalibrated?
Nope, you already recalibrated it when you mounted regular high-quality tires. It's about as perfect as it will ever be now.