Camber is the tilting of the front wheels from the vertical when viewed from the front of the car. When the wheels tilt outward at the top, the camber is said to be positive (+); when the wheels tilt inward at the top, the camber is said to be negative (-). The amount of tilt is measured in degrees from the vertical and this measurement is called camber angle. Proper camber is critical to assure even tire wear.
Toe-in is the turning in of the front wheels.The actual amount of toe-in is normally only a fraction of one degree. The purpose of the toe-in specification is to insure parallel rolling of the front wheels. Excessive toe-in or toe-out may increase tire wear. Toe-in also serves to offset the small deflections of the wheel support system which occur when the car is rolling forward. In other words, even when the wheels are set to toe-in slightly when the car is standing still, they tend to roll parallel on the road when the car is moving.
Caster is a measurement of the angle between the steering axis and vertical, as viewed from the side of the vehicle when the wheels are in the straight ahead position. Stated another way, it is the tilting of the front steering axis either forward or backward from the vertical. A backward tilt is said to be positive (+) and a forward tilt is said to be negative (-).