Caster also helps the wheels to self-center. Because of the geometry of a properly-designed steering system, as the wheels turn away from straight ahead, the front of the vehicle is lifted. Gravity pushing down on the vehicle makes the wheels try to return to center. As the caster angle is increased, the tendency to self-center after a turn also increases. Vehicles with power steering usually have much more caster than those with manual steering because the increased steering effort is handled by the power assist. All this is designed into the car or truck when it's manufactured, and thoroughly tested before a steering system goes into production. Making radical (or sometimes minor) modifications without totally re-engineering the steering and suspension often results in not just annoying, but sometimes deadly changes in the handling characteristics.
Jerry
