Last year, I bought two 27" tires for my Univega. They lasted only a year, and I had around 1200 miles on them before they started cracking and I had to replace them. Since 27" tires are getting rather rare, I suspect the tires I bought had been in a warehouse somewhere for quite some time. I recently read an article in a vintage auto racing magazine that told about old new tires that had been manufactured years ago. It was by an engineer at Mickey Thompson Performance Tires. He was writing about people who own vintage race cars buying tires new (never used)for them that had been around a long time. He mentioned a test one can perform on the tires to determine when they might have been manufactured. He said take three new tires: one was manufactured five years ago, one was manufactured a year ago, and one was manufactured yesterday. He said to take your thumb nail and try to make an indentation in the tread. You will have trouble making any indentation in the 5 year old tire. You can make an indentation in the one year old tire, but t the indent will disappear quickly. On the one day old tire, the indentation will remain quite a while before it goes away. The point he was making was a five year old tire will not perform well because it has dried out and won't grip the track surface. You can also tell it's old because it will take on a grey color. The UVL rays have gotten to it and have taken some of the black out (rubber is naturally white). I can see this on my car. Three of the tires (four years old) are a much lighter shade of black than the new tire I bought recently.
Contrary to this approach, my Trek dealer says most of the Tour d' France teams actually age their tires a year or more before putting them on competition bikes. Why is this? I would think that they would want a newly made tire to get maximum grip, especially for speeding down the Tour's mountain ultra-fast switchbacks at 40 mph. Can anybody shed some light on this?