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.
Alignment Basics
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 five factors involved in setting the alignment to
specification: caster, camber, toe, thrust and ride height. The following brief
discussion of each aspect will help you understand the process and spot
potential problems.
Caster
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.
Camber
Viewed from the front of the vehicle, camber describes the inward
or outward tilt of the tire. The illustration below 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.
Toe
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
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.
Misalignment and Tire Wear
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 treadwear 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.
Worn Parts
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.
