Answer: There are no expiration dates on tires. It seems that everybody from the NHTSA (National Highway Traffic Safety Administration), to the Rubber Manufacturers Association, to Click and Clack (The Tappet Brothers, hosts of “Car Talk”) all agree that there should be an expiration date. The problem is that no one can figure out how to determine an expiration date. So for now, the Department of Transportation (DOT) requires that tire manufacturers include a code on all tires indicating the date that the tire was manufactured. This is like putting the date that the cow gave the milk on the side of a milk carton rather than an expiration date.
The reason that it is so difficult to put an expiration date on a tire is because there are so many variables that contribute to the life of a tire. These include mileage, proper inflation, environment in which the tire is used, damage from road hazards, storage condition (ultra-violet rays from the sun and ozone in the air contribute to deterioration), what is used to inflate the tires (air or nitrogen), chemical composition of the tire, and the amount of time between its manufacture date and its sale date (it’s not unusual for a tire to be sold two of more years after it was manufactured).
One thing that just about everyone agrees with is that tires degrade over time…even if they are never actually used.
British tire makes recommend replacing tires every ten years, regardless of the mileage. Interestingly, they recommend that tires that have never been used (such as spare tires) be replaced every six years. Click and Clack recommend “every six years or so.” Every other source that I checked recommended between six and ten years. So unscientific as it may be, ten years from the date of manufacture seems to be the maximum recommended life for a tire.
To find out when a tire was manufactured, locate the long DOT code on the sidewall of the tire. The last four digits will indicate the week and the year. For example: 4208 indicates that the tire was manufactured during the 42nd week of 2008.
Yours is a classic case of “good news and bad news.” The good news is that you don’t have to waste your time checking the manufacture date. The bad news is that you should replace your tires. Then again, for many of us, any excuse to get new tires is good news.