More info on this topic:
http://www.goodyear.com/rv/tirecare/...placement.html :
TIRE REPLACEMENT GUIDELINES
Goodyear does not state a "uniform" replacement age for RV tires because there are many conditions that dictate a tire's safe and effective life span. Some factors that influence how long a tire will last are:
Usage per year - more frequent usage will result in longer life
Vehicle storage practices (6 months loaded with little or no rotation is not good!)
Usage in warmer climates can also negatively impact a tire's overall life due to greater extreme ozone exposure
RVIA (Recreational Vehicle Industry Association) says, ”Statistics indicate that the average life of an RV tire is five to seven years.“
Couldn't find the reference again, but these tires are commercial trailer tires, also.
Like many others, the failures I have reported here were tread seperation, the carcas was just fine and still holding pressure.