In February 2008, the owner of a 1998 Ford Explorer in Georgia needed a new tire for his SUV and ended up buying a used one. When he was driving two weeks later, the tread suddenly separated from the tire. The Explorer went out of control and hit a motorcycle, killing its rider. An analysis of the used tire revealed that it was nearly 10 years old. More recently, an investigation into the cause of the accident that killed the actor Paul Walker revealed that the Porsche Carrera GT in which he was riding had nine-year-old tires. The California Highway Patrol noted that the tires' age might have compromised their drivability and handling characteristics, according to the Los Angeles Times. These incidents illustrate not only the potential danger of buying used tires but also the perils of driving on aging tires — including those that have never spent a day on the road. For years, people have relied on a tire's tread depth to determine its condition. But the rubber compounds in a tire deteriorate with time, regardless of the condition of the tread. An old tire poses a safety hazard. For some people, old tires might never be an issue. If you drive a typical number of miles, somewhere around 12,000-15,000 miles annually, a tire's tread will wear out in three to four years, long before the rubber compound does. But if you only drive 6,000 miles a year, or have a car that you only drive on weekends, aging tires could be an issue. The age warning also applies to spare tires and "new" tires that have never been used but are old. What Happens to a Tire as It Ages? Sean Kane, president of Safety Research & Strategies, Inc., compares an aging tire to an old rubber band. "If you take a rubber band that's been sitting around a long time and stretch it, you will start to see cracks in the rubber," says Kane, whose organization is involved in research, analysis and advocacy on safety matters for the public and clients including attorneys, engineering firms, supplier companies, media and government. That's essentially what happens to a tire that's put on a vehicle and driven. Cracks in the rubber begin to develop over time. They may appear on the surface and inside the tire as well. This cracking can eventually cause the steel belts in the tread to separate from the rest of the tire. An animation on the Safety Research & Strategies Web site shows how this happens. Improper maintenance and heat accelerate the process. Every tire that's on the road long enough will succumb to age. Tires that are rated for higher mileage have "anti-ozinant" chemical compounds built into the rubber that will slow the aging process, but nothing stops the effects of time on rubber, says Doug Gervin, Michelin's director of product marketing for passenger cars and light trucks. How Long Does a Tire Last? Carmakers, tire makers and rubber manufacturers differ in their opinions about the lifespan of a tire. The National Highway Traffic Safety Administration (NHTSA) has no specific guidelines on tire aging and defers to the recommendations of carmakers and tire manufacturers. Carmakers such as Nissan and Mercedes-Benz tell consumers to replace tires six years after their production date, regardless of tread life. Tire manufacturers such as Continental and Michelin say a tire can last up to 10 years, provided you get annual tire inspections after the fifth year. The Rubber Manufacturers Association says there is no way to put a date on when a tire "expires," because such factors as heat, storage and conditions of use can dramatically reduce the life of a tire. Here's more on each of these factors. Heat: NHTSA research has found that tires age more quickly in warmer climates. NHTSA also found that environmental conditions like exposure to sunlight and coastal climates can hasten the aging process. People who live in warm weather and coastal states should keep this in mind when deciding whether they should retire a tire. Storage: This applies to spare tires and tires that are sitting in a garage or shop. Consider how a spare tire lives its life. If you own a truck, the spare may be mounted underneath the vehicle, exposed to dirt and the elements. If your spare is in the trunk, it's as if it is "baking in a miniature oven," says Dan Zielinski, senior vice president of public affairs for the Rubber Manufacturers Association. Most often, the spare never sees the light of day. But if the tire has been inflated and mounted on a wheel, it is technically "in service," even if it's never been used, Gervin says. A tire that has not been mounted and is just sitting in a tire shop or your garage will age more slowly than one that has been put into service on a car. But it ages nonetheless. Conditions of use: This refers to how the tire is treated. Is it properly inflated? Has it hit the curb too many times? Has it ever been repaired for a puncture? Tires on a car that's only driven on the weekends will have a different aging pattern than those on a car that's driven daily on the highway. All these factors contribute to how quickly or slowly a tire wears out. Proper maintenance is the best thing a person can do to ensure a long tire life. Gervin recommends that you maintain proper air pressure in tires, have them rotated regularly and have them routinely inspected. To help identify the age of your tyres, each one is imprinted with a coded date which tells you when that tyre was manufactured. The four-digit codes are usually located in a window on the tyre sidewall. The first two digits of the code represent the week of production during the year (from 1 to 52) while the second two digits represent the year of manufacture. In this example, the manufacture date code is 1413 - where 14 denotes the week of manufacture and 13 represents the year, meaning this tyre was made in the 14th week of 2013. If your tyres are printed with only a 3-digit number, it means your tyres were manufactured before 2000 and should be replaced asap. If your tyres are older than 5 years old, you should consider replacing them. Tyre ageing is commonly identified by small cracks, known as crazing, which appear in the tyre sidewall. This is brought about when UV light oxidises the rubber causing it to dry out. While tyres contain anti-oxidising chemicals which significantly slow down the rate of ageing, this wax-like substance is only released when the tyre is in motion. Therefore, if the tyre is not used frequently or is stored away ineffectively, they will age more quickly rendering them unroadworthy when returned to use. Low mileage, older cars tend to be most at risk from premature ageing - as drivers assume the tyres are still in good condition if they have plenty of tread. Premature tyre ageing can affect safety and increase the risk of tyre failure. For this reason, Kwik Fit urges drivers with tyres that are six years old or more to have them checked professionally to ensure they are still safe for use. Remember to check additional tyres such as spare wheels or those fitted to caravans and trailers as these tyres typically see less use and will be more susceptible to tyre ageing.
