[mgarvey]

Most insurance companies will consider new wheels a modification and charge extra - more so if you buy them aftermarket and they aren't factory fitted.

In terms of impact on the car, they'll obviously affect the ride and fuel economy to some extent, though this appears less of an issue on the F30 than it was on the E90 (from my limited experience of driving a few different F30's).

If you have aftermarket alloys and aren't fitting the latest generation runflats that the F30 uses, there may be differences in terms of ride and handling, but I only have experience of this on the E9x.