Scrub radius

In an automobile's suspension system, the scrub radius is the distance in front view between the king pin axis and the center of the contact patch of the wheel, where both would theoretically touch the road.

The advantage of this is that the tire rolls as the wheel is steered, which reduces the effort when parking, provided you're not on the brake.

More scrub radius adds to road feel by pushing the inside wheel into the ground.

A vehicle provides stable handling without any of the drawbacks of high positive caster because of SAI.

Conversely, when the lines intersect above the road, negative scrub radius is present.

When the pivot point is in the exact center of the tire footprint, this causes scrubbing action in opposite directions when the wheels are steered.

Negative scrub radius decreases torque steer and improves stability in the event of brake failure.