Tires, like most other auto parts, are built to withstand a great deal of wear and tear. Unlike other car parts, however, tire manufacturers always give an estimate for about how long a tire should last. The estimates themselves can range greatly for each tire, but you'll usually see a manufacturer listing of how many tens of thousands of miles you may expect out of that particular tire.
When it comes to car part longevity, however, there are always circumstances when the auto part information given by a manufacturer may not apply. In the case of tires, the estimate of how long a tire can last is based primarily on the tread wear. But some safety advocates want to add an expiration date of six years onto each tire, regardless of how much tread is left on them. The reason for setting up this six-year standard is that some research has shown that after that amount of time passes, tire failures dramatically increase. The tire industry has not yet set up its own estimate, partly because it doesn't want to give consumers the idea that its tires are guaranteed to last that long [source: Holguin].
Although there isn't a set expiration date as of yet, companies like Ford Motor Company already encourages its customers to scrap their tires if they're more than six years old [source: Holguin]. But how can you determine the age of a tire?
You can tell how old a tire is by looking on the tire's sidewall. There are lots of markings ranging from the type of tire, a speed rating that corresponds to a maximum safe speed your tire can sustain, the size of the tire and also when the tire was made; however, if you look after the Department of Transportation (DOT) letters, you'll see another list of numbers. If the tire was made before the year 2000, you'll see three numbers after the DOT letters; the last number indicates the year the tire was made. On newer tires, those manufactured in 2000 or later, you'll see four numbers. The first two numbers indicate the week it was built and the last two digits specify the year the tire was made. So, for example, if you see a "297" the tire was made in 1997, or if you see a "2409" that would mean that the tire was made in the 24th week of 2009 [source: Holguin].
So now we know how to determine how old a tire is and that some car manufacturers and safety groups encourage a six-year limit on tire age. But how does a tire's age affect its performance? Read the next page to find out.