saw this elsewhere so did a bit of copy/paste HTH
This information & diagrams are to help you understand offsets & PCDs (Pitch Circle Diameter).
OFFSET
To work out the offset the wheel must be measured accurately using the following steps and using
diagram 1
[/img]http://img.photobucket.com/albums/v712/carl010_2/diagram_02.jpg[/img]
diagram 2
Measure the overall width of the wheel - OW *
Measure the ‘T’ dimension, which is the measurement from the back of the bolt up face to the outside of the inner rim
Divide the overall width by two which gives you the centre line.
Minus the ‘T’ dimension from the centre line.
* Please ensure wheel has equal size kerb edges.
PCD
“The Pitch Circle Diameter is the diameter of the circumference of the centre line of the drilling holes.â€￾
diagram3
This can be four, five or six lug and can be measured as shown in Diagram 3. The easiest way of measuring four or six lug wheels is to take two diagonal holes and measure from the outer edge of one hole to the inner edge of the second hole.
With five lug wheels this is not possible as there is not two diagonal holes, therefore the simplified way would be to measure the outer circumference and inner circumference of the drilling holes. The difference should be divided by two added onto the smaller circumference or deduced from the larger circumference.
CENTRE BORE
“The centre bore is the location hole machined in the centre of the wheel.â€￾
This varies from one vehicle to another. It is essential, the wheels purchased have the correct centre bore for the vehicle they are to suit, otherwise you may experience balancing problems.. Therefore to obtain the correct fit for the vehicle the correct spigot rings must be inserted into the rear of the wheel.
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