What Is Offset
WHAT IS WHEEL OFFSET?
The offset is the distance from the hub-mounting surface to the wheel's true centerline. It is measured in mm and can be either positive or negative. A positive offset means the hub-mounting surface is closer to the outside edge of the wheel, while a negative offset means the hub-mounting surface is closer to the inside edge of the wheel.
A wheel with too little positive offset will be closer to edge of the fender. This can cause clearance issues between the tire and the fender. One that has too much positive offset will be closer to the suspension components and could cause the tire to rub on them. Wheel width, offset, and its accompanying tire size all determine how a particular wheel/tire combination will fit on a given vehicle. Offset also affects the scrub radius of the steering and it is advisable to stay within the limits allowed by the vehicle manufacturer. Because wheel offset changes the lever-arm length between the center of the tire and the centerline of the steering knuckle, the way bumps, road imperfections, and acceleration/braking forces turn into steering torques (bump-steer, torque-steer, etc.) and thus, will change the drivability of the vehicle depending on wheel offset. Likewise, the wheel bearings will see increased thrust loads if the wheel centerline is moved away from the bearing centerline.
When choosing an offset for an aftermarket wheel, it is important to take note of the space between the outer edge of the wheel and the fender. Depending on the desired style, you may want to match the change in offset from stock wheels to the amount of space between the wheel face and the fender. For example, if there is 15 mm of space between the outer face of the wheel and the fender and you're wanting a flush fitment, you would want to go from a +45 offset to a +30 offset. This will bring the mounting surface of the wheel further inward towards the vehicle from the true center point of the wheel thus poking the wheel out by an extra 15 mm.