Wheel geometry: Caster
Caster is the angle with which the imaginary swivel-axis line deviates from the perpendicular, viewed from the side, and is specified in degrees.
When the imaginary swivel-axis line is inclined rearwards as illustrated, caster is said to be positive (+) and when inclined forwards it is said to be negative (-). The Saab 9 -3 has positive caster.
Caster tends to keep the wheels pointing straight ahead and helps the driver to steer a straight path. In addition, more powerful steering wheel return action is obtained with a greater caster angle.
Caster is not adjustable.