Tires: Shelf Life Of Tires, surface cracks, tire failure

Question
There seems to be a difference in the expert opinion on the need to replace tires after so any years. Some, like an ABC News 20/20 story, say 6 years is max. even if a tire has no surface cracks and is soft like new. Others, like John here at this site, say age has nothing to do with tire failure - it's manufacturing quality, maintenance, etc. I have a set of tires that have been on a car since '86, but they have not been abused and have no trace of cracking. They are soft and new looking. Must I change them anyway?

Answer
Bruce,

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 (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.

So, yes, tires that are from 1986 are too old - even if they do not show any signs of abuse and cracking.