The tires motorists depend on every day to help get them from here to there might be holding a secret that could prove catastrophic.Not many people think about the age of their tires. Most think mileage ratings are the only determining factor in how long tires will last. Drivers should also consider how old their tires are -- not when they were bought, but when they were made, Call 6's Rafael Sanchez reported.Safety advocate Sean Kane has spent years investigating tire failures. His group, Safety and Research Strategies Inc., documented 140 crashes involving death or serious injuries that he claims were caused by tires made at least six years before the wrecks."An old tire is like a ticking time bomb in many ways," Kane said. "You don't know what's going on inside it. That's what makes it so dangerous."The parents of Bobby Crane believe their son died because of an old tire. The day before his 18th birthday, Crane and his brother were in the family's SUV when it flipped.Police blamed tire tread separation. The tire in question was a spare that the Cranes put on the SUV less than a month before the crash.A tire expert hired by the family determined that the tire failed because it was 14 years old."If I knew a tire could age to the point it was unsafe, I would never have allowed my sons to take that trip with that tire on their car," said Jack Crane, Bobby's father.The Cranes settled out of court with Firestone.The crux of the concern is that as tires age, the chemicals and glue that holds the layers together degrade, along with the rubber. That means the layers can come apart, leading to failure on the road.The National Highway Traffic Safety Administration knows rubber tires ultimately break down, so the government agency is currently developing a test to determine how aging changes tire performance.Kane said he hopes the NHTSA mandates expiration dates on tires six years after it was manufactured.Five major automakers, BMW, Chrysler, Ford, Toyota and Volkswagen/Audi, already warn against using tires beyond the six-year point, and three tire producers -- Bridgestone-Firestone, Continental and Michelin -- recommend a 10-year age limit.The Rubber Manufacturers Association, which represents tire makers, disagrees with age limits. They contend that factors such as storage, maintenance and weather are more important."Tires are safe. They're one of the most highly engineered products in existence today," said Dan Zelinski of the Rubber Manufacturers Association. "There is no information that can tell you exactly when, just because of its age, that a tire should be removed for performance reasons."Call 6 found numerous tires on central Indiana store racks that were made more than six years ago.At a Wal-Mart on Indianapolis' south side, Call 6 found non-used tires that were made in 2001 and 1999. A Car-X store on North Michigan Road was selling three non-used tires made in 2001.At a Big O Tires shop on Indianapolis' northwest side, Call 6 bought two non-used tires that were made in 2001.Call 6 also found plenty of used tires that were well beyond 6 years old.At two Goodyear stores, Call 6 found tires that were made in 1998 and 1997. Some of the tires had cracks in the sidewalls and treads.The stores have done nothing wrong, and there is nothing that prevents them from selling the tires. However, Car-X managers quickly took action after Call 6 brought concerns to them.The company said it ordered all stores to check each tire and "return or destroy any tire in their inventory over six years of age."In a statement sent to Call 6, Wal-Mart said it follows all National Highway Traffic and Safety Administration standards."Should the NHTSA create a ruling related to age of tires and its effect on the safety of our customers, we would of course comply," Wal-Mart said in the statement.Big O Tires provided a similar response. It also referred Call 6 to a 2006 news release from the Rubber Manufacturers Association.The tires that most tire shops put on cars are stored in areas to which consumers typically don't have access -- where they can't easily be checked before a consumer has them put on their vehicle.Even if a consumer does see the tire, it isn't exactly easy to decode the manufacturing date, which is printed on one side.The manufacture date can be determined from a code with 10 to 12 characters. The last grouping of numbers from that code discloses the week and year the tire was made.For example, a tire coded with 4807 means it was made in the 48th week of 2007. Tires made before 2000 end with just three numbers. A tire coded with 447 means it was made in the 44th week of 1997."Tire age is one of those issues that's completely under the radar screen for the average Joe," Kane said.Many tire companies advise customers to get rid of tires when they are 10 years old, regardless of condition.