http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=267The 6-7 years tire life expectancy was old rule for passenger car tires.
Bare in mind car tires have about 1/8" sidewall, while 22.5" tires over 1/2" (although I did not see RV series tires)
At present time each manufacturer has different recommendation, while most of them oscillate about 10 years with annual inspection after 6.
The best IMHO is Continental
Continental wrote:
Since service conditions vary widely, accurately predicting the service life
of any specific tire in chronological time is not possible.