I am a little over cautious when it comes to tires and bearings.
I replace tires after 5 years. NOW this depends on if the trailer sits during the winter. As all tires are made to "rotate" and while doing this the chemical in the tires lubricates the tires. If the tire sits still then no lubrication. Thus the 5 year replacement.
Also each spring when I get the trailer out out "inside" storage I take it to schwab (west coast) and have the bearings packed and brake shoes checked.
So far no problems from tires and bearings, and also we are not overloaded.
Mike & Emily
2007 Fun Finder X 160