Tire shelf life

Inspired by Susan's tread separation, I searched the 'net and couldn't find anything on this topic. So I'm re-posting here where it might get more views.

Contrary to Sheldon Brown's assertion, I don't believe that a hard or dry-rotted tire is safe. Maybe for low-speed tooling around, but not when traction is important, particularly cornering traction (commuting in traffic, descending, group riding).

Input, anyone? My instinct would be that the shelf life of a bicycle tire would be somewhat shorter than that of a motorcycle tire, but I really have no idea if the tread is even made of the same materials.

No answers, but another question: Why are certain tires recommended to be aged (for example, at least 6 months). I know Bike Friday lists that for some of their tires. Any ideas?

CA

I think it not only depends on how long tires are stored, but where they are stored (thinking back to the Discovery team and them keeping their tubulars in a wine cellar to age...). If the tires are out in the sun they are likely to dry and glaze much more quickly than ones that are stored somewhere cool and dark....

I think it also depends on the type of tire.

Actually, I just realized not too long ago that my mountain bike has the original tires and tubes on it. My mountain bike is from 1994! How is that possible? They seem fine, they certainly hold air, and the last time I rode it (about 6 months ago) I rode it hard and they held up great. I just don't get it.