Who carries a spare tire, other than the one around the waist?
I've never had one on my dumptruck. My C2500 I removed that spare to the front, along with the spare from a 96 equal I had. Ran both original spares until two yrs ago. My dually may have a spare..........
Not sure I have literally used or needed a spare but 2-3 times in 35 yrs of driving. If I had an SS on the rear of either dually, not sure I would worry about two sizes, only something that will be equal in diam to ea tire, that would allow me to get to a repair shop. Beyond that.....no reason to carry a spare in the years I have been driving.
I could see the issue with a SS hitting the ground and needing a new rim with a single. Tandems not as much. I do see SS's on many different types of tractors and trailers. Some probably make sense, others not.
Marty