For years, people have relied on tread depth to determine when to replace a tire. If the tread passes the "penny test," they assume the tire still has life, regardless of how old it is, which can be a fatal mistake. Old tires are dangerous, regardless of tread depth. While there's no federally sanctioned safety guidance on when a tire is too old to be safe, many carmakers recommend replacement at six years from the date of manufacture.
Old tires have been the culprit in fatal accidents. Here are just two examples:
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 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.
In a more recent and high-profile example, the investigation into the cause of the 2013 accident that killed the actor Paul Walker revealed that the Porsche Carrera GT in which he was riding had 9-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.