Over at The Lemon Law Blog, attorney Mark Anderson highlighted a problem that most Americans are unaware of: It could be dangerous to buy new tires that are more than six years old. A report by the newsmagazine 20/20 dove into the issue, finding that stores – even the big box retailers – can let new tires site on the shelves for years.  Apparently, even if tires have never been used, after six years they begin to dry out and have a greater likelihood that the tread will peel off the tire. When that happens, a vehicle can swerve violently and crash.

The thing is, even if a tire looks fine on the outside and has a lot of tread depth, hidden problems can be lurking inside. According to 20/20, Ford has requested that the U.S. government adopt a regulation that requires a six-year expiration date for tires. The Rubber Manufacturers Association has fought such a move, and the government hasn’t taken action.

When shopping for new tires, how can you tell when they were manufactured? Look for a code on the side of the tire that starts with DOT. Go to the end of the string of numbers and look for a (hopefully) four-digit number. The number 4202, for example, means that the tire was manufactured in the 42nd week of 2002. A three-digit number indicates that the tire was made in the 1990s. So, the number 414 means that the tire was manufactured in the 41st week of 1994.

If you want to see when the tires currently on your car were manufactured, you’ll probably have to crawl underneath and look for the code on the side of the tire facing inward. Given that there have are many fatalities due to tire failures, it’s probably best to play it safe.