The Diameter of your rim is measured from bead to bead across the face of the rim, not the total diameter from lip to lip. This is a common mistake when measuring wheels; the distance measured by the total diameter of the wheel can be as much as an inch larger than the measurement from bead to bead. This results in ordering a wheel that is one inch too large for your application. The diameter of the rim is displayed as the first number in a wheel description. Example: 12x4. The number ‘12’ is the diameter, and ‘4’ is the width of the wheel.
The width of your wheel is measured from bead to bead and is also commonly measured incorrectly. Improper measurement of the width could result in poor fitment under your trailer and may rub or not fit at all. The width of the wheel is displayed as the second number in a wheel description. Example: 15x6. The number ‘15’ is the diameter, and the ‘6’ is the width of the wheel.
Here is a diagram on how to measure a trailer wheel to ensure an accurate measurements.
Offset is also commonly measured as back spacing or rear spacing, but it actually measures the distance between the wheel’s mounting pad and the centerline of the rim. When the mounting pad directly aligns with the wheels center, it has a ZERO offset. If the mounting pad is closer to the back side of the wheel, it is known as a NEGATIVE offset. When the mounting pad is closer to the face or street side of the rim, it is known as a POSITIVE offset.
The easiest way to measure the offset of a wheel is to lay it face down on a flat surface. Now, lay anything with an absolute straight edge across the back of the wheel and measure the distance from the mounting pad, to the straight edge. Then flip the wheel over, measure again from the mounting surface to the straight edge (this time on the face of the wheel) and record that measurement. The difference between the two measurements is your offset.
There are many different bolt patterns in the trailer industry. For bolt patterns with an EVEN amount of bolt holes, measure from the center of one hole, to the center of the hole directly across from it. For 5 lug rims, measure from the outside most edge of a bolt hole, skip a hole, to the center of the next hole.
5 bolt patterns can also be verified by measuring the distance between the center of one bolt hole, the center of the bolt hole next to it. See measurements below:
Most automotive wheels are Hub Centric – they rely on the center hub of the wheel to carry the weight. All trailer wheels are designed to support the weight of the trailer on the lug studs. Therefore, all of our wheels are lug-centric. With that being said, all of our wheels will work for your application as long as the center bore is equal to or greater than the diameter of your hub and the bolt pattern matches.
If you study a wheel closely, you may notice a letter (J,JJ,k, etc.) stamped along with your rim dimensions. This simply designates the bead contour or bead profile of your rim. In other words, it is the area that the tire bead and the wheel meet. Most trailer wheels have standard bead profiles. When choosing a replacement trailer wheel, this is typically not a point of concern.