A lot of theories on tire care is based on old technology. Nowadays, with the synthetics, different formulations, etc., a lot of that is old school. As mentioned, the big killer is sun/ozone, and chemicals. Of course, never park a rig where the tires sit in gasoline, oils, etc., that may have been spilled or are on the surface of the parking spot. Another reason to "lift" a rig by the frame is to prevent a "set" in the springs (if you have them), but that takes a LONG time to happen. Another problem are the oils in a tire. If tire{s} sit for a long time, the oils used in manufacturing will "settle out" and the tire will actually dry out, hence the cracking. What keeps tires actually healthy is running them, so they flex and keep the oils distributed. Tire experts always say it is far better to wear a tire out, than to let it sit and "rot/dry" out.
The one exception to this is if anyone (I can't imagine who) still has bias ply tires. They will take a "set" quickly, and beat you to death until they get "warmed up" from driving a ways.
This is more applicable to us "boomers" who can actually remember bias ply tires!
