Alignment is one of the key maintenance factors in getting the most wear
and performance from your tires. In addition, wheel alignment provides
safe, predictable vehicle control as well as a smooth and comfortable ride
that's free of pulling or vibration. Today's modern suspensions require a
precise four-wheel alignment that can only be achieved through a modern
alignment system. This applies to both front and rear wheel drive vehicles.
Aligning a car or truck involves the adjustment of the vehicle's suspension, not the tires and wheels. The direction and the angles that the tires point in after the alignment is complete, however, are critically important. There are four factors involved in setting the alignment to specification: caster, camber, toe and ride height. The following brief discussion of each aspect will help you understand the process and spot potential problems.
Caster is the angle of the steering axis (the part of the suspension that supports the wheel and tire assembly). Viewed from the side of the vehicle, an imaginary line drawn between the centers of the upper and lower ball joints forms an angle with true vertical; this is defined as caster. The illustration to the right shows whether this angle is referred to as positive or negative. Caster is important to steering feel and high-speed stability.
Viewed from the front of the vehicle, camber describes the inward or outward tilt of the tire. The illustration to the right shows whether this tilt is referred to as positive or negative. The camber adjustment maximizes the tire-to-road contact and takes into account the changes of force when a vehicle is turning. Camber is the one adjustment that can be set according to driving habits. Generally, if you drive more aggressively when cornering, more negative camber can be set. If you drive on highways and do very little hard cornering, more positive camber can be set.
Viewed from above the vehicle, toe describes whether the fronts of the tires are closer (toe-in) or farther (toe-out) apart than the rears of the tires. The illustration below shows this relationship. Toe settings vary between front and rear wheel drive vehicles. In a front wheel drive vehicle, the front wheels try to pull toward each other when the vehicle is in motion, which requires a compensating toe-out setting. A rear wheel drive vehicle works just the opposite, necessitating a toe-in setting. Stated differently, toe is set to let the tires roll in parallel (at zero toe) when the vehicle is in motion.
Ride height is simply the distance between the vehicle's frame and the road. This is the reference point for all alignment measurements. Vehicle customizing will often include raising or lowering the vehicle. Don't forget to have your vehicle aligned afterward. Also, this rule applies if you put a taller or shorter tire on your vehicle.
By now you may have concluded that poor tire wear and misalignment are closely related. That is true, of course. But what can be done to minimize this condition? It turns out that many of these misalignment conditions can be easily "read" by your tire dealer; and they can recommend the appropriate solution, which will be "get an alignment." For your assistance, the following troubleshooting guide will help you see what your tire expert sees. Armed with this knowledge you can check your tires periodically. Remember that a knowledgeable glance at your tires on occasion can pay big dividends.
|Misalignment Condition||Tire Wear Symptom|
|Incorrect Camber Setting||Premature smooth wear on either inside or outside shoulder|
|Incorrect Toe Setting||Feathered wear across tread, raised tread block edges|
|Incorrect Caster Setting||Excessive shoulder wear, tread blocks show "heel-toe" wear pattern|
|Unequal Caster setting (either right or left side is out of specification)||Sharp pulling necessitates steering compensation and feathered wear|
|Unequal Toe setting (either right or left side is out of specification)||Sharp pulling necessitates steering compensation and feathered wear|
|Combination of two or more settings are out of specification||Irregular tread wear with feathering and smooth spots|
This is not meant to be an exhaustive listing of all the possibilities. However, if you learn to spot these symptoms early, you can get a lot more wear from your tires. Remember that tires take the brunt of many problems. Simply replacing the old ones is not a solution. Shortly after replacing your old tires, your new tires will begin to reflect the same problems if you have not made the appropriate alignment changes.
Very often a worn suspension part is the cause of an alignment problem. On older vehicles, worn springs can lower a vehicle's ride height, altering its geometry and creating misalignment (all alignment settings refer to ride height). Weak springs can also contribute to uneven or "cupped" tire wear. Another common problem is worn ball joints. The symptoms here are erratic handling, slow steering response, and irregular tire wear. Finally, worn tie rods can allow the tire to wander left to right, effectively changing toe as the vehicle rolls down the road. Irregular feathering will develop on the tire tread when this is the problem. Again, this is not an exhaustive listing, but if you stay alert to these common problems, it may help you schedule an early visit to your mechanic and save on tire wear.