Centre Bore and P.C.D

Centre Bore

The centre bore is the diameter of the hole in the centre of the nave plate. To measure this, measure from one side of the centre hole to the opposite side, as the diagram shows.

Pitch Circle Diameter (P.C.D.)

The Pitch Citrcle Diameter (PCD) is the diameter of the circle which passes through the centre of all the stud holes. There are two measurements that can be taken to find this. If there is an even number of studholes, you can measure the PCD or the chordal length, but if there is an odd number of studholes, you can only use the Chordal Length method.

If your wheel has an even number of stud holes, you can measure the PCD. To do this, measure from the centre of one stud hole to the centre of the stud hole opposite, as the PCD measurement on the right of the diagram shows.

To make this slightly easier, you can also measure from the edge of one stud hole to the same edge on the opposite stud hole, as the PCD measurement on the left of the diagram shows.

If it is not possible to take this measurement, for example, if the stud holes opposite are too abdly damaged, you can also use the Chordal Length method.

Chordal Length

If your wheel has an odd number of stud holes, the most accurate way to measure the PCD is by measuring the Chordal Length. To do this, measure from the centre of one stud hole to the centre of the stud hole next to it, as the measurement on the top of the diagram shows.

Again, to make this slightly easier, you can also measure from the edges of the stud holes, as shown at the botttom of the diagram.

This measurement is then multiplied by the factor value in the table, which will equal the PCD.