Wheel Specification: Offset, Bolt Pattern and Center Bore
Wheels and rims, what’s the difference?
Wheels are commonly referred to as the rims. Rims and wheels are two different things. Rim is a part of the wheel. Rims are the outer circle on which the tires are mounted. Hub, spokes and tires are part of a tire.
When purchasing wheels it is important that the wheels specification matches with your vehicle. Determining if a wheel fits on a vehicle is based on offset, center bore and the bolt pattern.
Offset of the wheel is the distance between the centerline and the surface of the wheel on which hubs are ascended. There are three types of offset that could be found negative offset, positive offset and zero offset. Lets discuss all of them.
1) Zero Offset: Zero offset of the wheel are those that do not have any distance between the centerline and hub mounting surface at all. The below diagrams shows that the offset mounting
surface is in the center of the wheel.
2) Positive Offset: Positive Offsets are the ones that have the hub mounting surface forward and is at the front or outside of the wheel. Positive Offset wheels are found on late rear drive cars or the ones with the front wheel drive
3) Negative Offset: Negative Offsets are the ones with the hub mounting surface shy from the front side of the wheel and more towards the back of the wheel or the brake side of the wheel’s centerline.
Bolt pattern or bolt circle is the diameter of an imaginary circle formed by the centers of the wheel lugs. Bolt patterns can be 4-, 5-, 6-, or 8-lug holes. A bolt circle of 4×100 means the lug pattern is 4 on a circle with a diameter of 100mm.
Center bore is the hole at the middle of the wheel on the hub of the car. Wheels are manufactured in huge numbers, they are not made with any vehicle’s center bore in mind, hence hub rings are always recommended. Most custom and aftermarket wheels are created with a center opening that will fit a variety of automobiles. Hub rings ensures that there are no fitment issues between wheels and hubs when fitting with each other.
Wheels can be non-hub centric by design, generally known as lug centric tires. Torquing is crucial to twisting the lug components with the vehicle on the jack as this process allows the bolts to center the rim and torque down.