Scrub Radius - Scrub Radius

Scrub Radius

The scrub radius is the distance at the road surface between the tire line and the SAI line extended downward through the steering axis.

The line through the steering axis creates a pivot point around which the tire turns. If these lines intersect at the road surface, a zero scrub radius would be present. When the intersection is below the surface of the road, this is positive scrub radius. Conversely, when the lines intersect above the road, negative scrub radius is present. The point where the steering axis line contacts the road is the fulcrum pivot point on which the tire is turned. Scrub radius is changed whenever there is a change in wheel o/s as on the t/l where the wheels are pushed outboard causing scrub radius to become more (+). Older cars tended to have very close to zero scrub radius but often on the (+) side, newer cars with ABS all have negative scrub radius (that's why all the newer cars have the wheels o/s more inboard).