Tire question

[Cavman]

Currently have the 333s (staggered 275/315) with summer performance tires (20" runflats and no spare due to 3rd row seating)

Am planning on driving from Kansas City to Steamboat, CO and am a little worried about getting a flat tire in Western Kansas that is more than 150miles (run flat limit) from a BMW dealer and/or a tire store that would have 275 / 315s in stock.

My newbie question to the board is this: are my rims the same width despite having different width tires on them? Meaning, do the 275s in front have spacers to push them to the edge of the rims (i.e. the 333s are the same width front and back)? Or are the rims different widths to match the width of the tire that is sitting on the rim?

I love the look of the staggered tires but it does make for worrisome travel when the route will take you far from a BMW dealer.

Would be willing to purchase a set of 20" all-season 275s (with spacers?) to run on all four 333 rims but don't know if that is possible. Or would I have to buy new rims too?

Worst part is, I already have a set of dedicated Pirelli Scorpions mounted on 214s for winter so this would be yet another set of tires! Ha.

Hope my questions makes sense. I want to keep my 333s but would be willing to swap the rubber on them from staggered setup to a consistent width all the way around so as to get peace of mind as we embark on our road trip.

My sense is that a tire dealer (Firestone/Goodyear etc) would be more likely to have a 275 all season in stock than a 275/315 summer performance tire.

Any help appreciated and if my questions aren't clear please let me know and I will try to explain it better. Am not very mechanical so I apologize if these questions are comically stupid.

Thanks in advance.