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 (-).
Although it is measured using a special instrument, it can usually be seen by observing the location of the upper and lower control arm ball joints. A line drawn through the center of these two points represents the steering axis. When looking straight downward from the top of the upper control arm, you can see if the ball joints are not aligned, indicating that the caster angle is more or less than 0 degrees. If the vehicle has positive caster, the lower ball joint would be located behind the upper joint center line. If the vehicle has negative caster, the lower ball joint would be located in front of the upper joint center line.
Camber is a measurement of the wheel tilt from the vertical direction, when the wheel is viewed from the rear of the vehicle. Camber is negative when the top of the wheel is inboard and positive when the top is outboard. Always check for bent, damaged or worn suspension components before determining that adjustment is necessary. The amount of tilt is measured in degrees from the vertical, and this measurement is called the camber angle.
Toe is a measurement of how far a wheel is turned in or out from the straight ahead direction. When the front of the wheel is turned in, the toe is positive. When the front of the wheel is turned out, toe is negative. An incorrect toe setting can affect steering feel and cause excessive tire wear.
Stated another way, toe-in is the amount that the front of the wheels are closer together than the backs of the same wheels. The actual amount of toe-in is normally only a fraction of a degree.