Wheel Measurements & Dimensions
Wheel Size: Wheels are sized according to their diameter and width measured from the tire mounting surfaces, usually in inches. A wheel with a 17" diameter and 8.5" width would be listed as a 17 x 8.5" wheel.
Backspacing: The distance from the back of the wheel to the wheel mounting surface is called backspacing. This measurement determines how far out from the axle the wheel will sit and is a critical dimension for proper wheel fitting. Backspacing is often abbreviated as "BS" and measured in inches.
Offset: Offset is similar to backspacing in that it determines how far out from the axle the wheel will sit. It is measured in millimeters from the centerline of the wheel to the wheel mounting surface. A negative offset wheel sits outward while a positive offset wheel sits further inward. Offset is also sometimes listed as ET with ET45 being a 45mm offset.
Center Bore: The size of the hole in the center of a wheel is known as the center bore. It is measured in millimeters and is often abbreviated as "CB".
Lug-Centric: Wheels that place the weight of the vehicle on the lug nuts are called lug-centric and require a center bore that is simply large enough to clear the axle hub. Lug-centric wheels require tapered or ball style lug nuts.
Hub-Centric: Wheels that support the weight of the vehicle on the axle hub flange are hub-centric and require a center bore that offers an exact fit. Hub-centric wheels normally use flange style lug nut.
Bolt Pattern: The quantity and pattern in which the wheel's lug nut holes are laid out is referred to as the wheel's bolt pattern. The pattern is measured in inches or millimeters and is displayed as the number of lugs times the diameter of the circle. A wheel with 5 lugs on a 5.5" circle has a 5 x 5.5" bolt pattern.
For more on bolt patterns and lug nuts see our Bolt Pattern Guide