Tires: cracks in tires, 4 digits, xse

Question
I have read all of the questions about tire cracks but found no answer to my question.   I bought 4 USED Michellin X1 radial XSE tires 4 months ago. the y show a lot of small cracks in between the threads. I dont know if the SIZE and the DEPTH of these are considered on the normal range or if the SIZE and DEPTH are considered on the dangerous side.  Could you give me some more information about the sizes and depth of the cracks?  I am getting ready to go to Missouri [ I live in Florida]  but do not have the money for new tires. So i would like to know how to tell if these tires are relatively safe as far as the cracks. i looked at the tire and could not find a date. but these is what I found: AP   1652
                                06- 51637-01
                                P215/70R15   97t   M+ s
Could you tell if any of these is the DATE of manufacture? Thank you so much for your help. I learned a lot reading your answers.

Answer
Elaine,

Categorizing cracks is a difficult thing.  So difficult that only a few people know that there has been a standard grading system developed - but it requires a sample board to be placed immediately next the thing being measured - and even at that there will be disagreement on degree.

My suggestion would be to have someone who does this regularly look at the tires - and that mean a retailer.

But here's another thing.  Did you read about the age of tires?  Tires more than 6 years old are iffy - especially if you don't know the history - which is the definition of what "Used" means.

Here's how to tell how old the tires are:

First locate the letters "DOT" on the sidewall of the tire.  Nearby will be the code.

DOT codes are a 10 to 12 digit number located near the letters "DOT".  BTW the digits can be numbers or letters.

The first 2 digits are a code for the manufacturing plant.  

The next 2 digits are a code for the tire size.  

The next 3 or 4 digits are a code for the type of tire.  

The last 3 or 4 digits are the date code.  The format is week/week/year/year or week/week/year.  These are always numbers.

Starting in the year 2000, the date coding used was 4 digits.  That means the largest number you should see for the year is 08.  Before 1999 the format was 3 digits.  1999 and 2000 are transition years, so you will find both 3 and 4 digits.

The date code only has to be on one side – and it is permissible for there to be a partial DOT code, so long as one side has the complete code.

Obviously, you didn't capture the DOT number.  Find it and you'll know how old they are.