One point I didn't read here
One point I didn't read here is that you better hope the offending tire's tread wear is within 3/32s of the new replacement tire if your car has X drive. Otherwise, you have to replace all 4 tires. My 528 X has Continental Conti Pro run flats. A new one comes with 10/32 tread. My tires currently are at 7/32 after 11,500 miles. So, I have to decide, do I replace my one tire that I need to now or go with all four with road hazard protection.
Non run flat is not an option as I have read that the suspension system is tuned with the heavier side walled run flat tires (and no spare; and I won't render my trunk useless by keeping a spare there).
Essentially, what I'm learning is that you should budget $1,000 in tires at a minimum in your first three years.