Hey guys I need some advice. I have a c300 2018 w205 sedan it has staggered wheels
front:
225/45R18
Rear:

245/40R18

I have continental run flat tires but I have been looking into getting a spare tire. Two different situations were I had the tire go out on me at the worst possible time. Just the other day I was evacuating for hurricane Ian and my tire exploded and I had to pay a guy $80 and drive 70 miles off route on the runflat to change the tire.

What tire size should the spare tire be? Should it be the same size as the front or rear tires?

Also if I were to switch all 4 tires for the same size what tire size would you recommend?

Thank you in advance I have been searching online for a couple of months and can't seem to find any answers and mercedes dealers will not recommend a solution as it is not what OEM suggests.