I recently saw a promotion at a major nationwide seller of automotive parts that seems to be a very common marketing ploy. "Buy three tires and get the fourth free"! Right! So, I went in to look at the tires and as expected, there were a lot of caveats. But, that was not what I was there for. I asked the salesmen how new the tires were and I was told that these were all recently delivered within the last week. So, I checked the date codes and they were all different, and worse, several of the tires were manufactured in 2009, and 2010. So why is that a problem? Because tires dry out and deteriorate over time. So, the tires on sale were already "aged" by four and three years respectively. And, dry tires tend to have hairline cracks that can lead to failure. So. how did I know when the tires were manufactured? Easy!
Since 2000, the Department of Transportation has required tire manufactures to supply a lot of information on the tire. By simply looking for the DOT designation with between 10 and 12 letters or numbers, it is easy to date the tire. The last 4 digits have the week and year of manufacture. In the photo on the right above we see 5107. This means that the tire was made during the 51st week of 2007. Also in the photo you can see that the temperature is "A". That is the best rating that goes from A to C. But, there is a lot more information about your tire. M+S is mud and snow, the manufacturer's name and more. There is a complete breakdown of the information on the National Highway Safety page from the DOT here. One caution I should mention is that the tire pressure relates to the maximum safe pressure for that tire, but is not the recommendation for your vehicle. Check your manual or the sticker on the driver's side door jamb for your car.
So, before your rubber hits the road, check for the age and other useful information. It could save your life!