To read the date code on a tire, look for the last four digits of the U.S. Department of Transportation number on the sidewall. The first two digits are the week the tire was manufactured, and the last two digits are the year.
A date code of 2112 indicates the tire was manufactured during week 21 of 2012. Tires manufactured after 2000 use the four-digit date code, while tires manufactured prior to 2000 use a three-digit code. In a three-digit code, the first two digits indicate the week of manufacture and the last digit is the year, but the decade is not specified. Some tires have a triangle following the number to indicate it was manufactured during the 1990s, but without that, it is difficult to tell the decade of manufacture.
The age of a tire is an important safety consideration, and even tires that have never been used, such as spare tires, can deteriorate over time. Exposure to heat and sunlight has been found to shorten the life of tires, and tires that have been mounted age more quickly than tires that have not been mounted and inflated. While tread depth is generally used to judge the soundness of a tire in use, there are no specific rules as to how old a tire can be and still be safe. Some tire manufacturers claim tires can last up to 10 years, but they recommend annual inspections after the fifth year.