From what I heard and learned, the chemical reaction between concrete and tires
occurs when the concrete is wet. This is like spring, fall, and especially
winter when you have the sloppy wet melting snow your tires are sitting in.
I had my camper sit for two years in the same spot on outside concrete, without
being moved. The only place that had weather checking was on the bottom of the
tires in the tread, the area that rested on the wet outside concrete. I now
park my tires on plywood, on this concrete during the winter. It is a chemical
reaction between wet concrete and tires parked too long. Asphalt and gravel
do no harm.
Brian