Sizing Up the Circle: How to Measure Your Trailer Hubs

With the multitude of components that make up your boat trailer, trailer hubs can sometimes get overlooked as a means to an end. They may just seem like a metal façade that holds the bearings and protects the seal, but your hubs are in fact an integral part of your trailer.

Because they are submerged in water so often, your hubs need to be routinely checked for erosion and rust. When a warm hub is submerged in cold water, the air inside the hub contracts and draws water in through the best of seals. Once parked, the water will settle at the lowest point in the hub. This is where corrosion and rust begin.

How to Measure Your HubsMost hubs come in a 4, 5, or 6 bolt pattern. If you need to replace your hubs, it’s important to measure the pattern in order to make sure you get the right size. A very common designation for boat trailer hubs would be 5 on 4.5 or 545 for short. This means that the hub has 5 bolts spaced evenly on a 4.5″ circle. To determine your bolt pattern, first count the number of bolts per hub. Then measure from the center of the hub to the center of one bolt and multiply that number by two. The result is your bolt circle. The pattern is written as “number lug on distance” or, for example, “5 lug on 4.5””. Most boat trailers hubs have this lug bolt pattern. It is also known as the small Ford bolt pattern. “5 lug on 4.75” is an old Chrysler product that may be difficult to find. “5 lug on 5” is the standard Chevy/GM lug bolt pattern and is commonly found on many utility trailers. “5 lug on 5.5” is also known as the “big” Ford bolt pattern and is used more recently on many Ford trucks. Once you have determined your hub pattern, you can confidently purchase new hubs.

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