Like most other things tires have a shelf life and just because the tires have never been mounted they can still be unsafe. Sidewall cracks and cracks in between the thread are just a few of the problems that are visible. Ten-year-old tires are still ten years old. I had a set of tires that had set mounted in the rafters of my garage for a number of years and they showed no side wall checking or cracks so using them to move a car about 20 miles looked to be safe. With all 4 wheels on the ground and 10 miles down the road they were shredding, I mean parts of tires were being left on the road. These just happen to be Power Ace tires that I was saving to replace a tire that happened to fail. Good thing I didn't. For more information see this article from Tire Rack...
http://www.tirerack.com/tires/tiretech/ ... techid=138
They say....
The British Rubber Manufacturers Association (BRMA) recommended practice issued June, 2001, states "BRMA members strongly recommend that unused tyres should not be put into service if they are over six years old and that all tyres should be replaced ten years from the date of their manufacture."
Not that this is the only article but it was one of the first that came up.
But I too keep a set of brand new bias ply tires that I have installed on my car for a show or two.
They hold air, but just looking at them makes me want to take them off.
Bill