The accepted specifications for cars are determined by an international agreement system instituted by SAE International, a worldwide organization that began as the Society of Automobile Engineers. One of its main functions is to set standards for automobiles and parts to be used on automobiles. The car wheel specifications set by this group are recognized by the U.S. Department of Transportation and other governments.
OEM is an acronym for original equipment manufacturer. It is a reference to a company that makes equipment for other companies to package and sell under their own name. OEM car wheel specs refer to the measurements that each wheel must have to be used by multiple automobile manufacturers.
The term "offset" refers to the distance from the hub mounting surface to the centerline of the wheel, measured in millimeters. A car's handling can be affected if the offset is not placed correctly.
Offsets come in three types. Zero offset is when the hub mounting surface is even with the centerline of the wheel. Positive offset refers to the wheel hub mounting surface found toward the front side of the wheel. These are usually found on front-wheel-drive cars and newer rear-drive cars. The third type of offset is negative, when the hub mounting surface is toward the back or brake side of the wheel's centerline.
The machine-punched opening on the back of the wheel that centers the wheel on the hub is called a center bore or simply bore hole. This hole is machine-drilled precisely to match the hub so that the wheels are positioned correctly for the lug hardware to be tightened.
These are exactly what the names state. The measurements refer to the diameter, width and weight of the tire to be used. They.are usually listed individually by front and rear tire dimensions.
The diameter of an imaginary circle formed by connecting the centers of the wheel lugs is called the bolt pattern or bolt circle. These patterns usually consist of four, five, six or eight lug holes. A bolt circle of 6x100 would indicate a six-lug pattern on a circle with a diameter of 600 mm.
