The machined center bore of a wheel determines the type of vehicle a wheel will fit. A center bore not matched to a vehicle hub will cause vibration. The vibration will make the vehicle uncontrollable at high speed. Wheel manufacturers enlarge their wheel's center bore to accommodate a wide range of vehicle types. Determining the center bore of your wheels will determine whether you require a hub ring to increase the strength of the wheel and reduce vibrations from the installed wheels.
Set a wheel, hub-side up, on a firm flat surface.
Press the zero end of a steel rule against one side of the center bore.
Set one side of a 4-inch combination square blade against the inside edge of the center bore, opposite the zero end of the steel rule.
Read the number of the steel rule aligned with the side of the combination square blade set against the center bore. That number designates the diameter of the center bore.
Convert the fractional portion of the measurement to decimals. Enter the non-whole number of the measurement into a calculator. Divide the top number and bottom numbers of the fraction to find the fraction's decimal value. For example, the fraction 3/16 would be three divided by sixteen for a value of 0.1875. Rounding the number to the nearest hundredth 0.19 shows the decimal equivalent of 3/16 inch.
