I've stored my previous Firebird and my current Camaro for the winter on concrete floors for months at a time without being started/driven/etc. and never had an issue with the tires. I overinflate them 5-10 PSI to try to help a bit. When I bought my Camaro a little over a year ago, it had tires on it from 2000-2001! Goodyear Eagle F1 performance tires. Hard and dry rotted, but no issues with flat spotting and it was stored by the previous owner for even longer periods of time without being driven but maybe a couple times a year. I replaced them shortly thereafter with some General GMAX all-seasons and had no issues with storing those, either. The Firebird I used to have had taller tires and again, no issues with those. BF Goodrich Traction T/A on that car on 16" wheels and I currently have lower profile tires on 18" wheels on the Camaro. These are pretty heavy cars, too.