For all the marvel of today's car safety systems — the networks of cameras, sensors and processors that help minimize driver error — the truth is that a car is still only as safe as the rubber that holds it to the road. That's why it's imperative to replace tires not only when the tread is worn but also when they're old, and even when it appears that plenty of life remains. Conventional wisdom says that if a tire passes the "penny test" (Lincoln's head is fully or partially covered by tread blocks when placing a penny upside down in the grooves), then it still has useful tread life. But this can be a dangerous mistake.
Like any rubber product, tires degrade with age. Regardless of tread depth, old tires can develop cracks and fissures that can lead to tread separation and loss of car control. While there's no hard-and-fast rule, and no federally mandated safety guidance on when a tire should be (ahem) retired, many carmakers and experts advise replacement between five and six years from the manufacturing date.
How dangerous are old tires? Here are a few examples:
In 2006, an 11-year-old boy was killed when his family's SUV rolled over on a California highway after the left rear tire's tread separated. An investigation revealed that a tire service center had installed the SUV's 12-year-old spare tire during a visit to replace the rear tires.
In 2008, the owner of a 1998 Ford Explorer in Georgia needed a new tire for his SUV and bought a used one. When he was driving two weeks later, the tread suddenly separated from the tire. The driver lost control and hit a motorcycle, killing its rider. An analysis of the used tire revealed that it was nearly 10 years old.
In 2013, actor Paul Walker died in an accident in a Porsche Carrera GT, one of the highest-performance models in the automaker's history. An investigation determined that the Porsche was driving on 9-year-old tires and traveling at speeds between 80 and 93 mph when the driver, Roger Rodas, lost control and collided with a power pole and several trees. Rodas was also killed.
These incidents illustrate the potential danger of driving on aged and used tires. For many drivers, old tires may never be an issue. If you drive 12,000-15,000 miles annually, a common amount for many commuters, a tire's tread will wear out in three to four years, well before the rubber compound does. But if you drive much less than that, or have a car that you only drive on weekends, aging tires could be an issue. And if you're buying a used car, there's a good chance it's riding on old tires. The age warning also applies to spare tires and even seemingly new tires that have never seen a mile but were produced years ago.