CHAPTER 12 WHEEL AND TRACK ALIGNMENT

One of the most neglected areas in vehicle maintenance is front-end wheel alignment and track alignment. To assure the proper steering control and normal wear of tires and tracks, you must maintain proper alignment. As an inspector, floor supervisor, or shop supervisor, it will be your responsibility to identify, adjust, or supervise the corrective measures needed to keep your equipment in a safe, operating condition. This chapter covers the principles and adjustments of front-wheel alignment and the principles of track alignment.

STEERING GEOMETRY

"Front-end alignment" refers to the relationship between the wheels of the vehicle and its suspension and steering. These relationships are calculated using angles known as steering geometry. These angles are camber, caster, kingpin inclination, toe, turning radius, and tracking. The following paragraphs cover the definitions of these angles and their effects:

1. CAMBER ANGLE. As viewed from the front of the vehicle, the camber angle is the degree to which the wheel tilts inward or outward (fig. 12-1). It is measured in degrees and changes with the load of the vehicle and suspension movement. Positive camber is the outward tilt of the top of the wheel, and negative camber is the inward tilt. It is shown by a line drawn through the center of the wheel and a second line drawn straight up and down. They should intersect where the tire meets the road. Camber is a directional control angle and a tire wearing angle.

Originally, roads were built with high crowns; that is, they were high in the middle and sloped downward to the sides. A large amount of positive wheel camber was needed for the tire to contact the road squarely. If the tire does not set squarely on the road, it will wear on one side and will not get a good grip for positive steering control. Modern roads, however, are made flat with very little crown, so less camber is needed for this reason.

Even with flat roads, some camber is generally desirable, because it moves the point of contact between the tire and the road more directly under, and closer to, the steering knuckle pivot. This makes the wheels easier to pivot and reduces the amount of road shock sent to the vehicle suspension and steering linkage when the wheels hit bumps. It also places most of the load on the larger inner wheel bearing.

To avoid some bad effects, the amount of camber must be carefully considered when a vehicle is designed. If you have ever rolled a tire by hand, you soon learned that you did not have to turn the tire in order to turn a corner. All you had to do was tilt (camber) the tire to one side, and it rolled around the corner like a cone. This is not desirable for the wheels of a vehicle. The cone effect

Figure 12-1. - Camber angle.