Wheel alignment refers to the condition and status of the wheels on an automobile. In simple terms, the wheels should be straight and in line with one another for the car to travel smoothly. With wheel alignment, it’s all a matter of angles. Two common key terms that apply to wheel alignment are perpendicular (straight up and down in relation to the road) and parallel to each other. If the wheels are adjusted properly in relation to each other and to the road, the car will not only travel smoothly but also will travel in a straight line without excessive wear on the tires.
Alignment is not the same as wheel balance, though both are important for the car to handle well. A driver will generally be able to tell quickly if a wheel is out of balance (slightly heavier on one side of the wheel than on the other). The vibration will be noticeable. Wheel alignment may not be quite as noticeable, except in trouble with steering or keeping the car traveling in a straight line.
For an experienced mechanic or wheel-alignment specialist, aligning the wheels on an automobile is not as complicated as the layman might think it is. There are actually three factors of measurement involved in wheel alignment. These are toe-in/toe-out, caster and camber. Each is a slightly different part of total alignment. One measurement that is not in the proper range will affect the handling and ride of the automobile.
In past decades, caster and camber were much more difficult and exacting, even for someone with experience. In recent years, a widely used item called the McPherson strut has eliminated much of the need for caster and camber adjustments. However, for purposes of understanding total wheel alignment, a brief look at each of the three factors is important.
Caster refers to the tilt forward or backward, while camber is the tilt of the wheels outward or inward (if you are standing in front of the car, for example). Both caster and camber measurements are measured as positive and negative. For example, positive camber means the wheels tilt out at the top. This is measured in degrees and when a wheel is perfectly straight up and down the camber is neither positive nor negative. Camber especially affects the proper wear of tires, which makes it very important in total alignment. Caster has little or no effect on tire wear, according to experts.
The third factor in alignment is “toe,” which measures whether the wheels are turned in or out, rather than straight ahead. This is the measurement that determines if the wheels are parallel to one another (as mentioned earlier). Toe has a significant impact on tire wear and on the comfort of the vehicles ride.
Most technical and academic material on wheel alignment also refers to a few other measurements that influence the handling of an automobile. These can include steering axis inclination, kingpin offset, ride height and set back. In the past, the task of aligning a car’s wheels was much more time-consuming than today, primarily because of improved car design and new technology in alignment equipment.