We had B F Goodrich and an experienced tire guy in TX who worked on Prevost told us that 7 years would be his recommendation. We replaced them at 6.5 years and they did have some cracking. We bought Michelins. The tire shop where we bought the Michelins said that we could probably get another year out of the Goodrich tires. They had photos of different degrees of cracks that he showed us for examples. We were heading out on a long trip out west, DH had heart surgery 6 months prior and we didn't want to risk a blow out. So the answer is "it depends". I would go see a Michelin tire shop that sells heavy duty tires and let them check against their example.