Car Tires With Plenty Of Tread But Too Many Birthdays: Reading The DOT Code Before The Rubber Cracks

Many car owners judge a tire only by its tread depth, yet rubber ages and hardens even when the car is rarely driven. Four small digits on the sidewall reveal when the tire was made.

In many home garages there is a car with low mileage because it only comes out on weekends or for the yearly trip back to the hometown. When checked, its tread is still deep and looks almost new. The owner feels safe. Yet those tires may already be seven or eight years old, and the rubber may have quietly hardened.

Tires do not only wear from rubbing against asphalt. Rubber also ages because of oxygen, heat, and sunlight. Over time, the oils and softening agents in the compound evaporate, so the rubber becomes harder and less flexible. Hard tires grip less, especially on wet roads in the rainy season, and are more prone to cracking on the sidewall. At high speed on a toll road with a full load, cracks like these can end in a torn or bulging tire.

The easiest way to find a tire's age is to read the DOT code on the sidewall. Look for the letters DOT followed by a string of letters and numbers. The last four digits, usually inside a small oval box, are the week and year of production. For example, 1001 means the tire was made in the 10th week of 2001, as shown in the photo above. The code is sometimes printed on only one side, so if you cannot see it from the outside, check the side facing under the car.