Trailer Wheel Hub assembly

Eastern Marine carries a wide selection of high quality cast iron trailer hubs in SAE and Metric sizes. Whether you are replacing your entire hub or re-building the old one, it is very important to use the proper size replacement parts.

The first specification to determine is the number of studs/bolts and the ‘bolt circle’ diameter. Most 4 lug hubs have a 4” bolt circle and most 5 lug boat trailer hubs have a 4-1/2” bolt circle diameter. Cargo and utility trailers with 5 lug hubs are commonly found with a 5” bolt circle. To correctly measure the bolt circle of a hub, measure from the center of the hub to the center of a stud and multiple that measurement by two.

The second specification to determine is the Inner and Outer bearing size. Most bearings are stamped with a reference number that can be used to easily identify its inside diameter (see chart in our wheel bearing section).

If the number is not available, the most accurate way to measure the bearing I.D. is with a micrometer. Be sure to check both the inner and outer bearing measurements before ordering. Hub length or bearing distance should also be considered. Some trailer manufacturers, such as LOADRITE & EZ-LOADER, use a ‘short hub’ on their 1” & 1-1/16” straight axles. The overall hub length is therefore shorter than most other standard boat trailer hubs.

When rebuilding the hub body with a new bearing kit remember to replace the inner and outer races or cups. Even if the cups don’t show sign of wear they should be replaced to maintain proper bearing tolerance. Thoroughly grease the bearings by working grease around rollers then pack the hub interior before installing a new grease seal in the back of hub.

Bearing grease quality and compatibility is another important consideration, especially for boat trailers that are commonly submerged in water after a long road haul. Marine trailer bearing grease provides outstanding water washout and excellent corrosion protection caused by salt water. It is important to determine compatibility prior to mixing greases of different base types. Incompatible greases can cause adverse chemical reactions, resulting in rust, pitting, scoring of metal, and breakdown of the greases ability to lubricate.