Our first coach was a 2001 Discovery that we bought in 2005, with fairly low mileage, I had no idea that tires aged out, loaned it to my son in 2007 and he had two blowouts on his trip to Kansas. We replaced all six tires and I learned a valuable lesson. This spring, I replaced all eight tires on the Beaver, at a little over six years old, good tread, since we were going to Alaska and I didn't want to take a chance. All looked good with no cracking, until we dismounted them and inspected the inside. They were disintegrating, and I was glad we changed. I have been told the only way to check is to dismount them for inspection.