Wheel sizing

Wheels: to size a wheel, you need to know 3 things. 1) Bolt Pattern, and diameter of bolt circle. 2) Offset 3) Wheel size (The diameter of the wheel)

1) Bolt Pattern. For a given vehicle you'll have to know how many bolt holes there will be, for instance in a 1974 MGB, there are 4 bolt holes. You want the diameter of the 'bolt circle' in the diagram below, if you see the bolt holes(the numbered circles), the dashed line equals the 'bolt circle'. The distance is expressed in MM, or sometimes inches. When you have 4 or 6 bolt holes, it's pretty easy, you get the distance from the center of 2 opposing bolt holes. For instance in the diagram 4hole_wheel.png you would go from the center of wheel hole #1, to the center of wheel hole #4. In a 5 hole system, it's a bit more difficult, as there are not opposing bolt holes, so you must 'invent' an imaginary bolt hole that is opposing, so you can then measure the distance. For example, a 1974 MGB is 4/4.5 so it is a 4 hole bolt pattern with 4.5" bolt circle. Or in millimeters, 4/114.3.

INSERT 4hole_wheel.png and 5hole_wheel.png

2) Offset.