Since the year 2000 the US Department of Transportation (DOT) requires that all tires display a standardized code on the outside of a tire that indicates the manufacturing location, tire size and approximate date and year of manufacturing. The code is still not very consumer friendly, but is easy to read if you know what it means.
Because the rubber in a tire starts to deteriorate shortly after manufacturing, it is important to know how old a tire is when you purchase it. The degradation of the rubber can be accelerated when cars and trucks are left in the sun in hot climates. Technically speaking, a tire is considered to be old when it is six or more years old. Some major tire retailers have been caught selling tires that are older than that, which can be a real safety problem, especially if you live in a harsh climate.
The manufacturing date can be found on the outside of a tire on a right end of a series of codes that follow the acronym DOT. The meaning of first sets of numbers are known only to tire manufactures, dealers and perhaps the DOT. The last four numbers are the important part because they identify the week and the year of manufacturing. Why did they choose to identify the week of manufacturing and not the exact date? Who knows. It was probably due to the fact that the date insert in the tire molds only had to be changed once per week.
In the example to the right, the last four digits identify the tire’s manufacturing date as “1811″, which means the 18th week of 2011.
Tires older than the year 2000 may have the code stamped on the inner sidewall of the tire, which makes it very difficult to read. There was no industry-wide standardization of codes prior to 200, but most dates prior to 2000 used a three-digit code to identify the time of manufacturing. Most manufacturers used a two-digit week designation with the last digit used to identify the year. A tire manufactured in the 14th week of 1995 would have a date stamp of 145. The problem with that is that a tire manufactured in the 14th week of 1985 would likely carry the same date stamp. Forcing manufacturers to use a four-digit date code is obviously an improvement in clarity.
I found this interesting video where John Stossel exposes the problem with a few major retailers who were caught selling very old tires to consumers. Watch the video and you will understand why it is important to check the manufacturing dates on all tires that you purchase.