I don't have this answer, either. Personally, I'd be willing to have a
10+ year old spare that was in visually good condition, with the
expectation that if I had to use it, it would be at moderate speeds just
long enough to get to the nearest tire dealer for a new tire.

Yeah, Eric. That's how I got to this point. The spare looks like new,
worked fine all the way home for four hundred miles even at
not-so-moderate speeds, and now I'm looking at it saying, "hey, do I
really need to replace it?"

Chip Bearden
ASW 24 "JB"