Tires: dry-rot, 4 digits, cold climate

Question
How long does it normally take new tires to dry-rot if they are being stored in an climate controlled garage?

Answer
Amanda,

From the day tires are produced, the rubber starts to deteriorate.  

In order to make sure they are still suitable for usage, most tire manufacturers limit storage to 3 years.

However, because "climate controlled" might mean a great range of things, tire manufacturers have been issuing bulletins that say that tires should be removed from service when they reach between 6 years and 10 years.  Here's my take on the difference:

If you live in a hot climate (AZ, CA, NV, TX, and FL) then the limit is six years.  If you live in a cold climate (MN, ND, WI, MT, etc), then the limit is 10 years.  States in between are  ..... ah ........ in between.

Please be aware that the rubber may be unsuitable for usage even though there are no cracks visible.  Cracking is the combination of the amount of flexing and the condition of the rubber itself.  It takes some degree of flexing for the cracks to appear.

This means that if cracks are present, the suitability of the tire for further usage should be questioned.  However, absence of cracks does not necessarily mean the tires are OK.

Here's how to tell how old tires are:

First locate the letters "DOT" on the sidewall of the tire.  Nearby will be the DOT code.  DOT codes are 10 to 12 digits long.  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 09.  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.