Here's how to tell:
Look on the sidewall of the tyre for the DOT symbol. Follow the line of text and numbers after the DOT symbol until you reach the end. If the tyre was manufactured in the year 2000 or later, the last 4 digits give the age. The last 2 digits give the year and the preceding 2 digits give the week of manufacture. For example, the code 3606 means that the tyre was manufactured in the 36 th week of the year 20 06 .
If the tyre was manufactured before the year 2000, the code is 3 digits long. Thus 366 would indicate the 36 th week of the 6 th year of the decade. Thus, before 2000, you had to make a judgement on which decade was intended. For example, 366 could mean the 36 th week of 199 6 or 198 6 .