Tire Aging and Date Codes

Here is something most people never think about. A tire with perfect tread depth can still be unsafe. Rubber deteriorates with age regardless of use. A tire that has been sitting in a warehouse or mounted on a vehicle that does not get driven much will look fine on the surface while the internal rubber compounds have hardened, cracked, and lost their ability to flex safely. Age kills tires just as surely as wear does.

Rubber is a polymer. Over time, oxygen breaks down the molecular chains in a process called oxidation. Heat accelerates it. UV exposure accelerates it. Even without those factors, the rubber slowly degrades from the inside out. The oils that keep the rubber flexible evaporate. The compound becomes brittle. Micro-cracks form in the sidewall and between the internal plies. These cracks may not be visible on the surface until the tire is well past the point of safe use. A tire that has aged out will not grip the road the way it did when new, and it is far more susceptible to sudden failure — a blowout from a pothole or road debris that a fresh tire would shrug off.

Every tire manufactured for sale in the United States has a DOT code stamped into the sidewall. The last four digits of the DOT code are the manufacture date. The first two digits are the week. The last two digits are the year. A code ending in 2319 means the tire was manufactured in the 23rd week of 2019. The DOT code is usually on only one side of the tire — if you do not see it on the outboard sidewall, check the inboard side. On tires made before the year 2000, the date code is only three digits, but you are unlikely to encounter those in service unless they have been sitting in storage for decades.

Most tire manufacturers and safety organizations recommend replacing tires that are six years old from the date of manufacture, regardless of remaining tread depth. Some manufacturers extend that to ten years as the absolute maximum. After six years, inspect the tire carefully for sidewall cracking, hardening of the rubber, and any signs of deterioration. After ten years, replace the tires regardless of condition or appearance. This applies to the spare tire too — the spare sitting under the truck bed or in the trunk ages at the same rate as the tires on the ground. A customer who has a blowout on a 10-year-old spare with full tread depth learned this lesson the hard way.