To determine a tire's age look on its sidewall (usually the back side) for the letters DOT followed by one or more ovals containing numbers. The last oval will have three or four digits. If there are three digits, the first two are the week of the year and the last digit is the year of manufacture (the digits 229, for example, would indicate the tire was manufactured in the 22nd week of 1999). To distinguish between the 80 and 90 decades, tires manufactured in the 90's will have a triangular mark to the right of the manufacture date.

Beginning with the year 2000 there are four digits. The first two are the week of the year and the last two are the year of manufacture (2301 indicates the tire was manufactured in the 23rd week of 2001).