Don wrote: they're just too old to be safe
Tis a factor to be sure, though I think that the pendulum has swung a bit far towards absolute caution on modern tires, and the current guidelines of "6 years in use or ten years in stock" makes no distinction between climates. In this mild climate, I'm happy to push toward ten years maximum service with regular inspection. I'm just not seeing tires dry out, stiffen, or show "checking" cracks like they did on the Gulf Coast or in Texas. No illusions here; I've created 'road gators' from flung tread twice- once from an old storage trailer and once on a restoration project en route to the body shop with 20 year old rubber (just wanted them to last till after the paint booth). Both times the casing remained intact (and finished the journey
At 19k miles per year, I don't get much time with a pair of front tires, so I'm willing to quickly use up older stock. If I were in a top-heavy SUV, truck or van, or a vehicle making trips far from home, not so much... Yes, I'm a cheapskate, like many i-MiEV drivers, but for the tire sins you can blame my college job in a Mississippi junkyard driving a salvaged truck on rubber pulled from wrecks!