A couple years back I acquired a set of wheels with some older tires on
them, for the Tiger. They were old, but had plenty of tread left. I
inquired to the manufacturer (Conti.) to determine their actual age, and
to get their opinion on longevity. I can't find their reply, but I
think I remember them saying that the didn't recommend using tires
beyond about 7 years, regardless of mileage. The rubber starts to get
hard. or something.
There was a question at the time, but I don't think that accident
involved an old tire.