Scrub radius is defined by SAE as kingpin offset, which is the distance between the two points created by the inter- section of the wheel centerline (centerline of tire patch) and the steering axis with the ground plane. The steering axis is determined by the kingpin index angle, which is the plane projected through the upper and lower ball joints and the wheel shaft joint. A zero scrub radius exists when the wheel centerline and the kingpin index intersect exactly at ground level. Positive offset occurs when the wheel centerline is located laterally inboard from the steering axis at the ground plane, while negative offset occurs when the steering plane intersects the wheel centerline above the ground plane.

Choosing a negative or positive scrub radius for a vehicle's suspension has emerged in recent years as a philosophical debate. For a passenger car strut suspension, achieving a negative scrub radius is at least a viable option. However, on SUVs and light trucks with 4WD and short long-arm (SLA) suspensions, packaging the wheel end components and achieving a negative scrub radius has been difficult or impossible. Demand for off-road capability, working payload capacity, and the required brake component size needed, makes achieving even a small positive scrub radius difficult or requires compromising brakes, steering linkages, or other suspension components.

Configuring the CV Hub wheel end design with several scrub radius settings was an attempt to show that it is feasible to achieve even a negative scrub radius in an SUV. Opinions about whether negative scrub in a light truck is what the average driver wants are mixed. However, there is a trend to provide improved vehicle-handling dynamics, which has increased the focus on reducing scrub radius to a small positive number.

• Wheel end design
• Theoretical work
• Vehicle testing
• Comparisons
• Summing up