I had to replace my right rear tire with my original spare tire because the nail that went though it wasn't patchable. My question is how long can I use the spare tire before I should be concerned about it being dangerous?

 

You are talking about the full size spare on the rear hatch correct? If that is the original tire, that means it is over 12 years old.

The estimated life for a tire, regardless of tread left, is about 6 years or so before it starts to deteriorate. Being that your tire is over twice that, it would not be wise to drive on, especially at high speeds. Have you ever tried to stretch an old rubber band? Instead of stretching, it snaps. The same thing can happen to your tire.

So to answer your question, there is no exact answer. It could work fine for a while, but there is a much higher chance of having the tire catastrophically fail and blow out.

I personally would not drive it anywhere, except slowly to get a new tire installed. If you cannot afford a new tire, even a good quality used one is a better alternative. It is not worth the damage to your car or the safety hazard to the occupants a blow out can cause.

Here is a good article on checking tire age if you are not sure:Tire Info

 

Thanks for the reply and yes it would be 12 years old by now and I'm trying to get new tires as soon as possible.

 

I'm assuming that 0401 means the fourth month of 2001 but do you know what 71 means or I'm reading it incorrectly?