Goodyear did say their G670s were good for ten years, but backed off on that.
We replaced our rear G670s at 9 years. They were just as supple and soft as the day they were made, inside and out and I kicked myself, and no discernible wear of the treads. I had previously put Michelin steer axle tires with separation grooves at both edges,on the front because the G670s rivered on the steer axle.
The rubber itself was in great shape. Goodyear put a lot of UV fighting compounds i n the motor home specific G670s. The New Michelins rode great an one required ounce of weight and the other none n the fronts. we kept our Mh stored inside in climate controlled environment though. We recently sold it and after sitting in the sun in Az for over a year one of the front ale Michelins the dealer said had a small crack. I didn't see it. The Chinese tires at first anyway did not have much UV protection in their tires an that is one of the major killers of Mh tires which are not driven as much as Semis.
Dealers say they cannot resale a semi or MH tire after five years.
The G670s do last longer than Michelins! The Chinese tires I have no experience nor heard any factual accounts of the life of those tires. If yu buy them keep them covered when parked and tire pressure kept where it should be is the only way know to judge. The five year rule for Michelins yes unless stored indoors.
The G670s a lot longer life if maintained and kept clean and stored indoors.
Dirt and lime suck the oils out of tires. This is just my opinion and not warranty.