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Wheel Measurments

We are often asked about offset and backspace for custom wheels. How are they measured? What is the difference between them? Wheelsforless fitment experts have been answering those questions since 1991!  you may finf these definitions of terms that are used to indicate various wheel measurements helpful to understand when determining correct fitment, especially on a custom application.
Mounting Surface: The mounting surface of a wheel is the flat surface on the backside of the wheel that actually comes in contact with the hub or drum.

Backspace: Backspace is the measurement from the mounting surface of the wheel (point the wheel actually comes in contact with the hub) to the very back edge of the wheel. Therefore the smaller the backspace measurement, the more the wheel will stick outward.

Offset: Offset is the measurement from the exact center line of the wheel to the mounting surface of the wheel. Offset is negative if the mounting surface is back of the exact center. Offset is positive if the mounting surface is front of the exact center. Offset is zero if the mounting surface is also the exact center of the wheel.

Pitch Diameter: Also known as bolt circle, bolt pattern, or "pcd" (pitch circle diamter). This is the diameter of the circle of the lug holes. The measurement is made from the center of the lug holes. For example, if there are five lug holes you would draw a circle through the five lugs and the diameter of that circle is the pitch diameter. If there are 5 lugs and the picth diameter is 4.5 inches then the bolt pattern is expressed as 5/4.5.

X-Factor: This is the measurement from the mounting surface to the spoke of the wheel. This measurement is important for oversized brake calipers. Oversized brake calipers will extend past the mounting surface, therefore, the x-factor must be know to ensure clearance.

Below is a diagram showing these measurements:

Also notice from the diagram that the rim width is measured between the rim flanges where the tire actually sits. Many people are confused by this because a wheel that is measured 8" wide is actually 9" wide from outside to outside of the wheel flange.

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