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PCD stands for Pitch Circle Diameter. Also Known as Bolt Circle Diameter (BCD). The Bolt Circle Diameter (BCD) (or Pitch Circle Diameter - PCD) is the diameter of the circle that passes by the center of the bolts.
This is very easily measured on wheels with even number of bolts by measuring the distance between the center of two opposite bolts in mm. In the diagram the blue circle highlights the BCD on a 4bolt wheel. The red line represents the diameter measured from bolt hole to the opposite bolt hole (for simplicity is easier to measure from one side of one bolt to the same side of the opposite bolt.
For wheels with uneven number the of bolts it where opposite each bolt lies the space between two bolts it can be calculated as function of the number of studs bolts and the distance between the centers of two adjacent studs. To calculate the PCD: Measure the distance between two adjacent bolts from the center of each hole as shown by the green line in the diagram on the right Use the appropriate formula for the given wheel 5 Bolts PCD = S =________mm 0.7071
In most cases the PCD of the wheel need to match precisely with that of the hub. If there is very small missmatch (no more than a few millimeters), it might be possible to use variance bolts to attach the wheel.