Quote Originally Posted by DebW
I think I've been riding on this tire for ~3 years, since I replaced my rear rim. I'd estimate it has 2000-3500 miles on it (I was off the bike for 4 months last year with a broken collarbone). Don't think I've ever worn tire tread down this far, but I typically do get multiple years out of a sewup. Guess that speaks to the cleanliness of the roads that I ride on.
I'm surprised it's lasted this long! I usually go through 2 sets of tires each year (though not always). I can't imagine having a tire last 3 years. I do tend to ride lighter tires, but they aren't racing tires or anything like that. And I always change them at the beginning of the outside riding season. Since the trainer eats tires, I can always use up the last little bit of rubber on used tires that way rather than risk it on the road.

Now that I'm riding in a more urban environment, I'm paying a lot more attention to the tires. Last thing I want is a blowout that could potentially cause me to lose control.

So, to answer your question, I'd say 0 miles outside. If you have a trainer, keep it for use with that or for "parts" to make little boot pieces. Old tires also make good dog toys and can be used to create interesting garden artwork!