See Figures 1 and 2
The procedure for checking and adjusting front wheel alignment requires specialized equipment and professional skills. The following descriptions and adjustment procedures are for general reference only.
Front wheel alignment is the position of the front wheels relative to each other and to the vehicle. It is determined, and must be maintained to provide safe, accurate steering with minimum tire wear. Many factors are involved in wheel alignment and adjustments are provided to return those that might change due to normal wear to their original value. The factors which determine wheel alignment are dependent on one another; therefore, when one of the factors is adjusted, the others must be adjusted to compensate. Descriptions of these factors and their affects on the vehicle are provided below.
Do not attempt to check and adjust the front wheel alignment without first making a thorough inspection of the front suspension components.
Caster angle is the number of degrees that a line drawn through the steering knuckle pivots is inclined from the vertical, toward the front or rear of the vehicle. Caster improves directional stability and decreases susceptibility to crosswinds or road surface deviations.
Camber angle is the number of degrees that the centerline of the wheel is inclined from the vertical. Camber reduces loading of the outer wheel bearing and improves the tire contact patch while cornering.
Toe-in is the difference of the distance between the centers of the front and rear of the front wheels. It is most commonly measured in inches, but is occasionally referred to as an angle between the wheels. Toe-in is necessary to compensate for the tendency of the wheels to deflect rearward while in motion. Due to this tendency, the wheels of a vehicle, with properly adjusted toe-in, are traveling straight forward when the vehicle itself is traveling straight forward, resulting in directional stability and minimum tire wear.
The Do-it-Yourself mechanic should not attempt to perform any wheel alignment procedures. Expensive alignment tools are needed and would not be cost efficient to purchase these tools. The wheel alignment should be performed by a certified alignment technician using the proper alignment tools.
STEERING AXIS INCLINATION
Steering axis inclination is the number of degrees that a line drawn through the steering knuckle pivots is inclined from the vertical, when viewed from the front of the vehicle. This, in combination with caster, is responsible for directional stability and self-centering of the steering. As the steering knuckle swings from lock to lock, the spindle generates an arc, the high point being the straight-ahead position of the wheel. Due to this arc, as the wheel turns, the front of the vehicle is raised. The weight of the vehicle acts against this lift and attempts to return the spindle to the high point of the arc, resulting in self-centering, when the steering wheel is released, and straight line stability.