The caster angle effects a vehicle's steering effort, stability at high speeds and cornering effectiveness. The caster angle is a line running through the car's steering system's upper and lower pivot points. Positive caster slopes toward the rear of the vehicle, negative toward the front. The front steering forks on a motorcycle are an easy-to-see example of how caster works. They point forward at the bottom and slope back at the top, causing the tire to remain stable. Positive caster is often engineered in racing cars since it improves high-speed stability and corning while increasing steering effort.
Park the vehicle with the front wheels on the turntables (set to zero). Point the wheels straight ahead. An absolutely flat surface is needed for accurate measurement.
Attach the gauge to the right front wheel hub. Turn the steering wheel 20 degrees right. Level the gauge and set it to 0 degrees.
Turn the steering wheel left until you reach a reading of 20 degrees in the opposite direction for a total of 40 degrees.
Hold the gauge at a 90-degree angle and the reading will be your caster angle for the right wheel.
Attach the gauge to the left front wheel hub while the wheels are still set to 20 degrees left.
Turn the steering wheel right until the wheel is turned 20 degrees right of straight ahead (turning 40 degrees total).
Hold the gauge at a 90-degree angle and the reading will be your caster angle for the left wheel.
If you don't have locking turntables, you can still measure the caster angle. Just have someone hold the steering wheel steady while you measure.
Setting a positive caster angle in a vehicle without power steering causes a noticeable increase in steering effort.