The caster is the tilting of the steering axis either forward or backward from vertical when viewed from the side of the vehicle. A backward tilt is measured in positive degrees (1) and a forward tilt in negative degrees.

On the short and long arm type suspension, you cannot see a caster angle without a special instrument. However, if you look straight down from the top of the upper control arm to the ground, the ball joints do not line up (fore and aft) when a caster angle other than 0 degrees is present. With a positive angle, the lower ball joint center line would be slightly ahead (toward the front of the vehicle) of the upper ball joint center line.