Editorial Comment:  Chris poses an interesting problem which may become more widespread if the use of runflat tires spread.

My experience with tires has always been to trust the recommendations of the manufacturer, since they design a car to perform in a certain way using certain equipment.

If you wish to stray from those recommendations, you need to expect results which are different from what you've been accustomed.

I would start checking with the BMW owner's manual or the dealer. Are runflat tires an option on this car, or are they installed with no alternatives offered?

If conventional tires are also offered and listed in the manual, then you may have no problem in using them. If they are not optional, then at the very least you can expect the car to perform and handle differently than they did with runflats.

If they handle and perform differently this, obviously will have an effect on the suspension, but the effect might be positive, or negative, depending on various factors, such as your driving style, the kind of roads you travel, etc.

Another issue to take into account is a legal one. Some areas make it illegal to drive without a spare tire (but may make exceptions for cars with runflat tires). This might be another thing to consider when making your choice.

Finally, what kind of tires are you considering as a replacement? Some high performance tires may be just as costly as the ones you're replacing, and often high performance tires tend to have a shorter treadwear
than standard tires.
TG