We could define the scrub radius as the distance in front view between the king pin axis and the center of the contact patch of the tire, where both would theoretically touch the surface. The line between the upper and lower ball joints of the hub is known as the kingpin axis. The top pivot point is the strut bearing whereas the bottom point is the lower ball joint in a Macpherson strut. The slope of the steering axis is measured as the angle between the steering axis and the centerline of the wheel. This implies that if the camber angle is variable within the pivoted points the scrub radius can be changed which could alter the width and offset of the tires on a vehicle. If the kingpin axis intersection point is inside the centre of the contact patch it is positive, if it is outboard the contact patch it is negative. The term scrub radius derives from the fact that either in the positive or negative offset, the wheel does not turn on its centerline (it scrubs the road in a curve) and because of the increased friction, more effort is required to turn the wheel. An advantage of a negative offset is that the geometry naturally compensates for split µ (mu) braking, or failure in any of the brake circuits. It also gives center point steering in the event of a tire deflation, which provides better stability and steering control in this emergency situation.