It would probably have been fine if you aired down and drove slower. Keep in mind it's an old tire and called a spare for a reason. Drive slower and more careful with spares if they are old.This tire was brand new (when I put it on my spare tire carrier 12 years ago). When I needed it, last week, it would still hold 50psi. This is a photo of it after 1 mile on a dirt road...
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NOTE TO SELF: Rubber doesn't like sun ;-)