[Ford56]

I've kept tires on my antique vehicles for over 20 years before changing them out. I've read that exposure to the sun is more damaging than just about anything else. I normally only put about 200 miles per year on any of the old vehicles. They are stored in dark garages, unheated and w/o air conditioning. I normally drive in the slow lane. I don't race or do turnpike cruising. I once had a set of replacement bias ply tires for 30 years, and never had any problems. The only reason I changed them was to go to radials. YMMV.