A caster adjustment is made to the front wheels of a car. It is an adjustment that sets the angle of the car wheel from the axis at which it pivots. This simply means that the wheel is connected to the steering pivot at an angle. The angle is the caster setting of the car. A mechanic or race crew will adjust the caster setting to get more performance out of their vehicles. Car manufacturers have extensive caster settings and have conducted a lot of research into making the right adjustments. The caster adjustment will affect how your car performs in many ways.
A positive caster adjustment sets the wheel forward from the pivot axis so the wheel draws forward into line as the vehicle moves forward. This can be related to the front forks of a bicycle wheel, which are set an an angle and connect to the wheel in front of the pivot axis (in this case handlebars) on the bike. That adjustment allows for better control during forward movement and makes the car fall back to a straight line after a turn.
A negative caster adjustment means the wheel is set behind the pivot axis a few degrees or more. This negative caster adjustment usually results in less control, since the wheels are free to turn on their own. Cars with negative caster will sometimes slide and sway from side to side while driving. This causes more fatigue in the driver as he constantly has to straighten the vehicle out.
Negative caster isn't always bad. Sometimes racing crews will use it to help their car perform better during a race. Setting the caster angle forward on one wheel and backwards (negative) on another wheel will cause the car to drift in one direction or another. This drift can be useful for the driver on loop race tracks where he is constantly making a left- or right-hand turn.
A caster adjustment is seldom made on street cars. The caster setting is made at the factory and does not have to be altered. Only in the case of customized vehicles, does a caster adjustment need to be made on street cars. Caster can be affected by lift kits which are installed on off road vehicles. These kits raise the chassis and therefore decrease the caster angle. That means a new caster adjustment must be made to get the wheels back in front of the steering pivot.
A caster adjustment is made by certified mechanics and auto repair technicians. It is a complex concept that involves a lot of math and geometry. A caster adjustment is made when caster correction ball joints and sleeves are installed into the car steering mechanism. These sleeves and joints will affect the angle of the wheels by pushing them further away from the axis of pivot, thus changing the caster angle. They can be installed with the existing parts, however the process is quite involved and will take one to two days to complete, even by a certified mechanic.
