From Tire Rack web site:
Determining the Age of a Tire
When it comes to determining the age of a tire, it is easy to identify when a tire was manufactured by reading its Tire Identification Code (serial number). Unlike vehicle identification numbers (VINs) and the serial numbers used on many other consumer goods (which identify one specific item), Tire Identification Codes are really batch codes that identify which week and year the tire was produced.
The U.S. Department of Transportation (DOT) National Highway Traffic Safety Administration (NHTSA) requires that Tire Identification Code be a combination of eleven or twelve letters and numbers that identify the manufacturing location, tire size, manufacturer's code, and week and year the tire was manufactured.
Tires Manufactured Since 2000
Today, the week and year the tire was manufactured is contained in the last four digits of the serial number, with the 2 digits used to identify the week a tire was manufactured immediately preceding the 2 digits used to identify the year.
Examples of tires manufactured since 2000 with this Tire Identification Code format:
XXXXXXXX 0600XXXXXXXX 060006 - Manufactured during the 06th week of the yearXXXXXXXX 060800 - Manufactured during 2000
And
XXXXXXXX 0608XXXXXXXX 060806 - Manufactured during the 06th week of the yearXXXXXXXX 060808 - Manufactured during 2008
While the entire Tire Identification Code is required to be branded onto one sidewall of every tire, current rules also require the first digits of the Tire Identification Code (everything but the week and year) must also be branded onto the opposite sidewall. Therefore, it is possible to see a Tire Identification Code that appears incomplete and requires looking at the other sidewall to find the entire Tire Identification Code (the use of a partial Tire Identification Code on the one sidewall reduces the risk of injury to the mold technician that would have to install the weekly date code on the top sidewall portion of a hot tire mold).
Tires Manufactured Before 2000
The Tire Identification Code for tires produced prior to 2000 was based on the assumption that no tire would be in service for ten years. They were required to provided the same information, with the week and year the tire was built contained in the last three digits. The 2 digits used to identify the week a tire was manufactured immediately preceded a single digit used to identify the year.
For example, if the Tire Identification Code on a tire reads:
XXXXXXXX 0680XXXXXXXX 060006 - Manufactured during the 06th week of the yearXXXXXXXX 06808 - Manufactured during the 8th year of the decade
While the previous serial number format identified that a tire was built in the 8th year of a decade, there was no universal identifier that confirmed which decade (tires produced in the 1990s may have a small triangle following the Tire Identification Code to identify the decade). The Tire Identification Code format used since 2000 accurately confirms the year.
And finally, hold on to your sales receipts. Most tire manufacturer's warranties cover their tires for four years from the date of purchase, or five years from the week the tires were manufactured. So if you purchase new tires that were manufactured exactly two years ago they will be covered for a total of six years (four years from the date of purchase) as long as you have your receipt. If you lose your receipt, your tires' warranty coverage will end five years from week the tire was produced (resulting in the tire manufacturer's warranty coverage ending only three years from the date of purchase in this example).
