Recently, my sister and her family were headed out on a family vacation. They were pulling their camper, as usual, and had 2 tire blowouts within 100 miles. After this experience, they replaced all four of their tires and continued on.
The primary question is: why did these tires fail? They were not overloaded, the pressure had been checked; they just failed (pretty spectacularly, too).
My personal opinion on this lies in the fact that these were original tires on a trailer bought in 2004. They had become too old and failed. This is yet another reminder that even though your tires may look fine and hold air pressure fine, if they are old, they can not be relied on.
The matter of how old is too old is up for endless debate, and I don’t want to rehash it here. I can only tell you what I do after looking at the information available and reading some of the arguments. I tend to be conservative, and replace tires (including the spare) every 5 years, no matter the tires’ condition. This gives me peace of mind while driving, and that is really the only reason I need.