Dear Car Talk:

We have a 2007 Toyota 4Runner with 80,000 miles on it. It is on its second set of tires. When we replaced the tires the first time, I think that we probably should have bought only three tires and used the full-size spare, which is on the same rim as the four tires on the ground. Now that spare is 9 years old. Is it too late to try to use it when we next replace the tires? Love your column.

-- Gary and Patty

Yeah, that spare's a little late to the party, guys. Nine years is too old to rely on a tire.

The tire manufacturers say a tire should be replaced after six years -- even if it's not worn out -- due to rubber degradation.

Even if you add a couple of years to that to account for the tire makers' desire to sell more tires, nine years probably is pushing it.

What you should have done is had your first set of tires rotated occasionally, and mixed the spare into the rotation. That would have gotten you a little more life out of that set.

And what you should do next time -- when you replace this second generation of tires -- is save the best used one as a spare, and put the 9-year-old spare in an assisted-rotating home.