Why Do Tires Have a “Born on” Date?

| October 1, 2012

tire tread depth

Tires are expensive, so we all try to make them last. You might know the “Lincoln’s head” rule for checking tread depth, but did you know tires can wear out, even when a vehicle is never driven? If yours are more than 6 years old, use DexKnows tires listings to find a vehicle repair shop that can take a look.

But before you rush out, there’s one important point to consider: How can you tell the age of your tires?

Molded into the sidewall of every tire is a 12-character Department of Transportation (DOT) code. More of a “born on” than a “best before” date, this tells you where and when the tire was made. The first eight characters are for the manufacturer and DOT, so ignore those and just look at the four numbers at the end. The last two give the year the tire was made, and the two to the left correspond to the week number. So, as explained on the Bridgestone/Firestone website, if the last four digits are “0709,” that means the tire was produced in the seventh week of 2009.

Why tires break down

Well, here’s the problem: Tires are complex products made from a mixture of manmade materials and natural rubber. Over time, chemical reactions break down these materials, making them harder and weaker. Tire manufacturers go to great lengths to ensure this happens very slowly, but they can’t prevent it. Adding to the problem, heat and sunlight accelerate the aging process.

When tires are taken out on the highway, they’re subjected to all sorts of loads and stresses. The older the tires, the greater the risk of failure. This is why leading manufacturers such as Michelin advise that tires be replaced when they are 10 years old. The DOT takes a more cautious line, recommending an annual check once tires turn 5 and suggesting that drivers consider new tires when they are over 6. (Visit the DOT’s Safercar.gov website for more details.)

When a vehicle is driven every day, it’s almost certain that the tread will wear out before age ends the life of the tire. The problem comes with vehicles that are only used occasionally. Classic or collector cars fall under this heading, as do the convertibles that only come out in the summertime in many locales.

But there are two other situations that drivers tend to overlook: trailers and the spare. Boat trailers, horse boxes and anything else that gets hitched up a few times a year all have tires that cover relatively few miles. As such, they are candidates for aged-related deterioration. The other tire that seldom gets used is the spare in or under your trunk.

Now, it’s possible that you’ve already checked your tires and found only an 11-character code. That’s bad news because it means that the tires were made before 2000. If that’s the case, those tires are overdue for replacement.

New tires are expensive, so it’s natural to make the ones you have last as long as possible. But after 10 years, perhaps sooner, a tire may not be safe. Check the date code, and if new rubber is needed, use DexKnows tire listings to find an auto repair place that can help you out.

Tags: , , , ,

Category: Auto Maintenance, Auto Parts, Autos

About the Author ()

After twenty years in the automobile industry the craft of wordsmith called. Putting down the wrench, Nigel picked up a keyboard on which to express his passion for all things automotive.