Trailer bearing protectors are spring-loaded metal caps that replace the dust caps on a trailer's hubs. This is especially true of boat trailers that enter the water when the boat is launched. The protectors keep dirt and water out of the trailer bearings and keeps grease inside the hub, even when submerged. Trailer bearing protectors have a spring inside to keep constant pressure on the trailer bearings in any condition, wet or dry. This keeps contaminants out while keeping towing and bearing grease in, prolonging the life of the tow bearings and reducing the need to repack or replace them every year or two. Dry or dirty bearings wear down over time, keeping the hubs from rotating freely.
In addition to the spring-loaded bearing protectors, additional protective equipment can further seal the bearings against road grime. Like the protective cover on the nose of a sports car, these additional caps are usually called "bras." They are cheap and easy to install over the bearing protectors. All told, the protective equipment will cost about $25 to $50, depending on the size of the towing trailer's hubs. Bearing protectors alone cost $20 to $40.
As inexpensive as this equipment is, this one-time cost might actually save you money in the long run. Read on to find out how.