Tires will degrade even if stored inside a building out of the elements. The fact is that oxygen will cause the tire to degrade. Oxidation, the same process that causes metal to rust, also affects the rubber of tires and can have very destructive results. In order to slow the process of oxidation, manufacturers usually equip tires with a waxy protectant that seals the rubber away from the oxygen in the air. Unfortunately, through the life of the tire this protectant begins to fade away, too, especially if the tire is not used. A 40 year old tire is worthless and should be recycled, Do not risk your life with a tire even 10 years old let alone 40.

If it is located in its cubby hole which is a dark place with no sunlight then the tire is perfectly fine. It is the sunlight that destroys plastic and rubber.

They say garbage bags last for hundreds of years...those are the garbage bags that are buried in landfills...with soil on top. Otherwise if exposed to the sun say as a protective cover over something you use only in the summer...the bags last one winter and then they break apart into pieces the size of quarters. Same age of bag used indoors will have a much longer shelf life.

Same for plastic paint buckets, garden hoses, Corvettes, boats.

The best use for a 40 year old tyre is to take it off the wheel, turn it in side out and fill it with soil. Then plant some pretty flowers in it.

Would I trust my life to it by using it ion a vehicle? Never! While you're at it think about changing the other four.

Rubber degrades over time, regardless of whether is was stored properly or not. Most all tire manufacturers recommend tire replacement after 10 years, or sooner, even if unused.

Unsafe for stopping as the rubber is dry and hard.

Nope - Time for new rubber.

Sure. Why not use it?

If my car (1975 AMC Hornet 4DR sedan) came with an original spare tire, completely unused, and never removed from the car itself...still inflated, in fact would that tire be reliable or should I get it looked at or replaced before relying on it in an emergency?

The car was kept in a garage and only have abouit 43,000 miles on it and the entire car is in absolutely beautiful condition. I drove 500 miles when I picked up the car, to get back home after purchasing it, on tires that were over 20 years old and it drove beautifully. So anyway, a 40 year old unused tire: any good or not?