Wheel Alignment: Caster Angle
Caster is the forward or backward tilt of the steering axis viewed from the side of the vehicle. Vehicles with SLA suspensions use the upper and lower ball joints to create the angle, and those with struts use the center of the upper strut mount and the lower ball joint as the angle.
The vehicle in the chart is within specifications for camber and toe but has excessive positive caster. This excessive positive caster will cause a shimmy at higher speeds and excessive steering wheel snapback. Vehicles that specify high positive caster usually have a steering dampener attached to reduce any adverse effects.
Zero caster is when the tire is true vertical. Negative caster is when the lower pivot point (ball joint) is toward the back of the vehicle compared to the upper pivot. Positive caster is when the lower axis is toward the front of the vehicle, and the upper pivot is leaning away from the front toward the rear. Most vehicles have positive caster because it provides greater feel and stability, helps the wheels track straight, and provides steering wheel return after turning.