Tires: tires, judgement call, 4 digits

Question
i have a sixteen year old volvo station, which has been maintained very well. about four or five years ago the tires were changed and i don't think that the car has been driven more than ten thousand kilometers since. the car has always been garaged. now i have been told that my tires have to be changed as it may not pass the test because the sidewalls are dry, the tread is good. my late husband always made sure that we had good tires and now i do not know what to do. how can i tell if there is a problem with the sidewalls by looking at them?
i have used your site a lot and have been very appreciative of the advise as it has been very good and am sure that this will be the same. it was my daughter who suggested that i contact this site before i rush to get new tires. many thanks. thelma
i want to thank you in advance for your advice and if it is appropriate, wish you and all of yours a very merry christmas and a good holiday season. thelma

Answer
Thelma,

You should look for small cracks in the sidewall.  That is an indication of the state of the rubber in the sidewalls - commonly called dryrot.

But this is judgement call, so I would get a second opinion.

But you should be aware that recent bulletins from the tire industry indicate that tires degrade simply due to time.  The age of a tire is important even if the tire is unused.  There some disagreement over how to best express this age limitation, but my take is:

If you live in a hot climate, then the limit is six years.  If you live in a cold climate, then the limit is 10 years.  In between is ..... ah ........ in between.

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 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.