Like everything else in life, tires get old. And just like us, they may look OK and be fine in everyday use, but they reach a stage where they are no longer able to perform at their peak, regardless of mileage.
Tires are a complex item developed with the use of many chemicals and other components. Scientists and engineers use these materials to arrive at a balance of wear, wet and dry grip, weight, noise and rolling resistance. Over a period of time – somewhere in the five-seven year range, the tire gets to the stage where it no longer is able to perform as intended.
How can you tell the age of your tires?
Look closely at the sidewall of a tire, near the wheel or rim. All new tires sold in North America since 2000 must carry a number that complies with a directive from Transport Canada and the U.S. Department of Transportation (DOT). That complex number, starting with the letters DOT, consists of 11 or 12 digits. It is known as the Tire Identification Code, and identifies where and when the tire was produced. The last four digits are the ones you are concerned with. For example 0508 would tell you the tire was produced in the fifth week of 2008.
If your tires are more than 6-8 years old they may well have past their “best by” date.
Tires generally loose their effectiveness after 6-8 years regardless of mileage. The most common cause of tire failure is overheating – whether through overloading or under-inflation, but after a period of time they harden and loose much of their grip and effectiveness in wet or dry conditions. Tires are a complex combination of rubber and a variety of chemicals. Molecules within that compound are activated every time a tire goes from cold to hot, hardening with each heating and cooling cycle. The oils contained within evaporate over time, further contributing to the hardening process.
The British Rubber Manufacturers Association has “strongly recommended” that unused tires should not be put into service if they are more than six years old and that “all tires should be replaced 10 years from the date of their manufacture.” Several European manufacturers of high performance cars state in the owner’s manual that “under no circumstances should tires older than six years” be used.
Don’t worry if the dates on your tires differ. It is nearly impossible to get a set of four new tires with perfectly consecutive dates, they are sent from different plants around the world to tens of thousands of distribution centers and then sales points so are often split up. You should be able to get four that were produced within a few months of each other. Reputable tire stores try to keep track of these numbers and rotate their stock accordingly.
Lots of us have older, restored or special vehicles that are driven very little. I’ve got a couple that accumulate less than 1,000-km a year. Obviously the tires will never wear out at this rate, and these vehicles are not driven aggressively so wear and performance are not the issue. But they will dry out and become less safe over time. The tread will become harder and not provide the intended grip. The sidewalls will develop cracks – which are more important. My advice? If it’s a daily driver, submitted to the full range of operating conditions tires should be changed after six or seven years. If it’s a low-mileage “special” driven sedately you can get a couple more years out of the tires.