Tire dating code
We argued that changing the DOM from the obscure week and year representation to something that was immediately accessible to the average person wouldn’t conflict with other possible tire aging requirements.
That might please the Rubber Manufacturers Association, which has increasingly become isolated in its view that tire age doesn’t matter.
So, if you had the number "329", that would indicate that the tire was made in August of 1999 (or at least that's what you'd have to assume).
The DOT added the fourth number because the "9" could also indicate 1989, 1979 or even 1969. What If My TIN Number Isn't As Long as It's Supposed to Be?
So, you can actually learn quite a bit from that TIN. Exposure to UV rays and other environmental conditions causes the rubber to break down over time. If a retailer tries to sell you an old set of tires, you'll be able to tell right away. You don't want that set that's been baking in the back of a hot warehouse for the past three years.
This could lead to a blow out, and cause an accident.