Caster Angle: Used to describe the front wheel alignment angle as the tilting of the steering axis either forward or backward from the vertical (when viewed from the side of the vehicle). A backward tilt at the top steering axis point is said be positive (+) and a forward tilt is said to be negative ( - ). Measurement is usually expressed as an angle
degrees and minutes. It is general practice that the vertical and steering axis centrelines both pass through the wheel centre.

This results in a caster distance, which can be described as being the distance in side view, between the point where the steering axis contacts the ground and the centre of the tyre ’ s footprint contact.