I have a fifth wheel with Goodyear G614 G rated tires. They still have very good tread and still look good but they were made in the 19th week of 2014. I read that you can go between 6 to ten years....
I got 9 years out of my XPS Ribs....until 1 blew out sitting in my driveway....no damage. I kept them covered, inflated a few PSI higher over the winter months, and applied 303 protectant quite often.