The 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.
Zero-degree caster is when the tire is truly vertical. A negative caster angle 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 a positive caster because it provides greater feel and stability, helps the wheels track straight, and helps the steering wheel return to center.
Steering Wheel Snapback
The vehicle in the chart is within specifications for camber and toe but has an excessive positive caster. This extreme caster angle will cause a shimmy at higher speeds and excessive steering wheel snapback. Vehicles with high positive caster usually have a steering dampener attached to reduce adverse effects.