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 just replaced mine at 5 years after watching a buddy have two blowouts on his 6 year old rubber. I suppose if they were Michelins maybe I'd go longer but the offshore **** they put on new trailers is just that. I rest a lot easier with a step up in load range, higher speed rating and new rubber. Well worth the $400 IMO.