Bearing intervals are driven by water intrusion far more than by mileage. A boat trailer that gets dunked needs attention several times more often than a utility trailer that never sees water.
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They hold slight positive pressure to keep water out, which helps, but they do not remove the need to open the hub and inspect. Overfilling them can also push grease past the rear seal onto the brakes.
A hub noticeably hotter than the others after a stint of towing is the usual first sign, often with a rumble or growl that changes with speed. Check hub temperature by hand at every fuel stop.
On a cheap single-axle trailer, fitting a new bearing and race set often costs little more than the grease and your time, and it resets the clock with known-good parts.
Method last reviewed 2026-07-29. Figures are guidance, not a substitute for the ratings printed on your own equipment.