This was always my issue with the e46 M3, I never planned on using the Mobility kit if i got a flat, for that reason i carried the 18" front in my trunk all the time. That sucked though since I usually only took the spare on long trips and thats when I needed the extra trunk space.
1.) How is the M5 trunk space? Is there much room left if i dumped a full size 19" wheel in there?
2.) Is there a space saver kit yet with a donut that will clear the F10 M5 front brake?