The age of a tire is a significant factor in vehicle safety, independent of how much tread remains. Even a tire with deep tread can pose a risk if the rubber compound has degraded over time. The Department of Transportation (DOT) code serves as the standardized identifier containing this crucial date information. This code allows consumers to determine the exact week and year a tire was produced, providing the necessary data for informed replacement decisions.
Locating the Date Code
The date code is part of the Tire Identification Number (TIN), a longer sequence beginning with the letters “DOT.” This entire sequence is permanently molded into the tire’s sidewall. While the full DOT code provides details about the manufacturing plant and size, the date code is always found at the very end of this string.
The complete TIN may only be visible on one side of the tire, requiring a check of the opposite sidewall if the code is not immediately apparent. The date code is a distinct set of four digits, sometimes enclosed in a raised rubber oval, separating it from the rest of the identification number.
Decoding the Tire Age
The current format for the date code is a four-digit number that precisely identifies the week and year of manufacture. The first two digits represent the week of the year (01 to 52), while the last two digits indicate the final two numbers of the year. For example, a code reading “3524” signifies that the tire was manufactured during the 35th week of 2024.
Tires manufactured before 2000 used a different, three-digit format that can be more ambiguous. In this older system, the first two digits represented the week, but the final digit represented only the last number of the year within that decade. The shift to the four-digit code in 2000 eliminated this decade-related confusion, ensuring a clear and specific date for all modern tires.
Why Tire Age Matters
Tire rubber compounds degrade over time through a chemical process known as oxidation, which occurs even when the tire is not in use. Oxygen permeates the rubber from the inside out, causing the material to become stiffer and more brittle. This internal breakdown is accelerated by exposure to heat, ultraviolet (UV) light, and ozone.
This degradation is particularly concerning because it affects the inner layers of the tire that bond the steel belts together. As the rubber stiffens, it loses its ability to flex, which can lead to the inner layers delaminating from the steel belts. This internal structural failure can result in sudden tread separation and catastrophic blowouts, even if the tread depth appears adequate.
Because of these inherent material changes, most vehicle manufacturers and safety experts recommend replacing tires that are six years old from the date of manufacture, regardless of remaining tread depth. Ten years is the absolute maximum service life advised for any tire, including the spare. Checking the date code provides the necessary information to adhere to these safety guidelines.