Dear Car Talk:

My 14-year-old Toyota RAV4 has a cover on the spare tire. I'd like to buy a bike rack that fastens onto the spare tire, but that would require removing the cover. I'm wondering if that will reduce the useful life of the tire. How useful is a 14-year-old spare tire? The new RAV4 models don't seem to have a spare tire at all. What do you think I should do?

-- Gordon

That 14-year-old spare tire probably is pretty useless at this point.

Actually, let me correct that: The thing a 14-year-old spare tire is best for probably is holding a bike rack.

I'm guessing no one has looked at that spare tire in about ... oh, 14 years. It's not on most people's to-do list: "Let's see ... quart of milk, call Mom, remove spare-tire cover and examine spare for sidewall cracks ..."

So, you should have your mechanic give it a once-over. If he tells you it's dried out and cracked and no longer viable, then it needs to be replaced anyway. (That's probably what he'll tell you.)

If, by some miracle, your spare tire has found the fountain of vulcanized youth under that cover, then you can keep it a little longer.

A cover probably does increase the useful life of a spare tire somewhat by keeping it out of direct sunlight. But even exposed to direct sunlight, a new spare will last at least six years, maybe longer -- by which time the car will either be dead, and you won't need the bike rack because the bike will be your only remaining vehicle, or you'll have to buy another spare tire for $75.

So, my advice would be to replace the spare, stash the cover, get the bike rack and figure that the health benefits of more bike riding will more than make up for the 12 and a half bucks a year the new tire will cost you.