Measuring your trailer rim's bolt pattern (bolt circle) can sound difficult, but below we'll show you an easy way to do it. Measuring the bolt circle is important when selecting a trailer rim that will fit nicely on your trailer. When measuring your wheel's bolt pattern what you are essentially doing is measuring the diameter of the circle that the lug holes are drilled on. Put simply, If you were to draw a circle through all the lug holes, the diameter of that circle, is your trailer wheels bolt pattern.
For trailer rims with an even number of lug holes, this is easy because there are adjacent lug holes. This allows you to measure from the center of one lug hole; to the center of the hole on the opposite side. Measuring trailer wheel bolt patterns with an odd number of holes (5-lug) can be a tad more challenging because no two holes are directly across from eachother. We have outlined an easy to follow process for measuring 4 lug, 5 lug, 6 lug and 8 lug wheels below. The principals shown below can be used to measure not only trailer rims, but automotive rims, lawn tractor rims, golf cart rims, etc.
Measuring 4-Bolt Patterns
Measure a four bolt trailer rim from the center of a bolt hole, skip one bolt hole and then the center of the next hole. Basically your ruler goes across the center of the wheel.
Measuring 5-Bolt Patterns
Because 5 is an odd number, no two bolt holes are directly across from one another.
Measure from the edge of one hole to the center of the other most across from it. The measurement you come up with (most commonly 4.5"), is your bolt pattern.
Measure the distance CENTER TO CENTER between two lug holes Next To Eachother and use the chart below to determine your bolt pattern.
If you measure:
2 5/8" - your bolt pattern is 5 on 4.5"
2 3/4" - your bolt pattern is 5 on 4.75"
3" - your bolt pattern is 5 on 5"
3 1/4" - your bolt pattern is 5 on 5.5"
Measuring 6 Bolt Patterns
Measure a six bolt wheel from the center of the bolt hole, skip 2 bolt holes and then the center of the next hole. Your ruler goes across the center of the wheel.
Measuring 8-Bolt Patterns
Measure an 8-bolt wheel from the center of a bolt hole, skip 3 bolt holes and then the center of the next hole. Your ruler goes across the center of the wheel.