I've had a lot of experience with motor home tires...they have much in common with the tires on our Imperials...long periods of sitting with infrequent periods of heavy use. 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. My 82 Imperial, by the way, has one 10+ year old Michelin which is a survivor-all three of its siblings have failed massively but I'm postponing new tires until after I have the car painted. I do keep the spare inflated... Phil Brust 73 & 82 Imperial