Caster – This is the angle of tilt of a line drawn from the center of the top ball joint through to the center of the bottom ball joint, compared to vertical. Caster aids the wheels to straighten themselves out after cornering, however the more caster you have, the more that you may have to fight the steering entering a corner. If the top tilts toward the rear of the vehicle, then it has positive (+) caster. If it tilts forward toward the front, then it has negative (-) caster.
Figure 4 – Positive Caster
Caster Split – This is the difference between the caster of the front wheels. If the left front is set at +1 degree and the right front is set at +3 degrees, then your caster split is 2 degrees (Right front(+3) –Left front (+1) = 2).