I've got 4+ years on my Power Kings.Last month I had the wheels off to repack the bearings.Also took them in toreplace the valve stems and had them balanced. I asked the tire tech to look them over really good when he was replacing the stems.. (One had an on going slow leak). Thinking he would be in for a sale, I am sure he gave them a good look. He reported they looked to be in good shape, should last at least 2 more years. The slow leak turned out to be a valve stem, the core was not in more thana quarterturn
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I do cover the tires when not in use because the sun shines on the curbside tires most of day where my trailer is parked. I don't have major mileage on them, may be around 14,000 miles. But some of those miles are pretty rough forestry service roads.
I also check the pressure every morning when on the road and make sure they are kept inflated at 65lbs.
I did notice the rear tire of each tandom pair was getting a little more wear than the front so I reversed their position when I remounted them. My trailer rides very level so I figure the rear tire must takemore abuse on the tight backing turns and such. When it comes time to replace I'll probably go with Maxxis but until then I feel fairly confident these Power Kings will not be a problem.