Chevrolet Equinox Service Manual: Scrub Radius Description Wheels

Ideally, the scrub radius is as small as possible. Normally,the SAI angle and the centerline of the tire and the wheelintersect below the road surface, causing a positive scrub radius.With struts, the SAI angle is much larger than the long arm/shortarm type of suspension. This allows the SAI angle to intersect thecamber angle above the road surface, forming a negative scrubradius. The smaller the scrub radius, the better the directionalstability. Installing aftermarket wheels that have additionaloffset will dramatically increase the scrub radius. The newlyinstalled wheels may cause the centerline of the tires to movefurther away from the spindle. This will increase the scrubradius.

A large amount of scrub radius can cause severe shimmy afterhitting a bump. Four-wheel drive vehicles with large tires use asteering damper to compensate for an increased scrub radius. Scrubradius is not directly measurable by the conventional methods.Scrub radius is projected geometrically by engineers during thedesign phase of the suspension.