[Mr70]

You got it Mike,but that's for tires made after the year 1999.Before 2000,the last digit is the last digit of the year manufactured,and the two numbers before that are the week in the year.
Example:...3197 DOT code after the year 1999 is 31st week of 1997.
3197 before 2000 is 19th week of a year ending in 7.This is where you have to figure out what year that last digit stands for.It could be 1967-77-87-97.
Now you have to understand the plant codes and what was up & running in those time frames at those locations to help narrow down the year manufactured.
This does not apply to ALL tires.