Just FYI, the tires on the rear of my 65 mustang which spends 99% of its time in the garage, are at least 12 years old now, and seem to be in perfect shape. No signs of dry rot or cracking, and have around 15000 miles on them. Of course I don't drive over 70 mph, but do drive as much as 100 miles in single highway trip. I agree with what Reddy45 says.