Tires - age BEFORE beauty - still a conundrum!

[DONALDDICKINSOND@xxxxxx]

In a message dated 4/20/2004 12:16:04 PM Eastern Standard Time, pbrust@xxxxxxxxxxxxxxxxxx writes: 
> The rule most motor home owners follow is: replace the tires every seven
> years regardless of wear. A blowout on an inside rear tire can cause several
> thousand dollars worth of damage so, even though the tires cost $3-400 each,
> the risk is too great to run old tires.

This seven year rule seems like a reasonable life for our Imperial tires, or as my calculus professor used to say "it is intuitively satisfying."  Is there any good research or tire evaluation by the industry to substantiate tire aging life?  As aging is dependent on many use and environmental factors it probably is far from an absolute, i.e., it would be defined such as "under normal aging conditions 96% of tires should be serviceable for 6 years."  But for safety reasons it is info we ought to know.