To understand caster you need to picture an imaginary line that runs from through
the upper ball joint and extends through the lower ball joint. From the side
view the imaginary line will tilt forward or backward. The tilting of this imaginary
line is defined as caster.
Caster is measured in degrees by using a caster camber gauge. If the imaginary
line described above tilts towards the back of the car, at the top, then you
will have positive caster. If the imaginary line tilts forward then you would
have negative caster.
Positive caster provides the directional stability in your racecar. Too much positive caster will make the steering effort difficult. Power steering will allow you to run more positive caster. Negative caster requires less steering effort but can cause the car to wander down the straightaway.
For oval track racing most racers run more positive caster on the right side tire than on the left. The caster split helps pull the car down into the turn, helps the car turn in the center and helps it stay hooked up on exit.
How much caster should you run? The amount and split depends on the type of
car and track conditions. The details should be worked out with your car builder
and through testing.
