Wheel alignment is the
geometrical relationship of the wheels to the vehicle
itself, to each other, and to the road. Ideally, all four wheels should
be aimed
straight ahead, parallel to each other, perpendicular to the road and perpen-
dicular to their respective axles. This will produce the least amount of
rolling
resistance, the least amount of friction, the least amount of tire wear,
and the greatest traction. The basic alignment angles are Toe, Camber,
and Caster.
Toe is the most important
wheel alignment angle because it has the greatest
effect on tire wear.
Improperly set Toe is
a bad condition to have because it causes the tires to
scrub as they roll along. For instance, only 1/8th inch of toe-out will scrub
the
tires sideways 28 feet for every mile driven. At this rate, it doesn't take
long
to wear down the tread.
When both front wheels are aimed straight ahead and the distance between the leading edges of both tires is exactly the same as the distance between the trailing edges, the wheels have "zero toe".
Toe-in means the front edges of the tires are closer together than the rear edges.
Toe-out is when the front edges of the tires are farther apart than the rear edges.
A classic symptom of toe misalignment is a feathered wear pattern across both front tires. The direction of the feathering tells you if the tires are toed-in or toed-out (rough edges towards the inside signal toe-in while rough edges to the outside indicate toe-out).
WORN PARTS AFFECT TOE ALIGNMENT
Worn or loose steering linkage parts shoud always be replaced. After the parts have been installed, an alignment will be needed.
Something else to keep
in mind about toe is that rear toe is just as important on front toe-
especially if a vehicle has an independent rear suspension or rear toe
adjustments. This includes most front-wheel and minivans as well as some
rear-wheel drive cars. Rear toe misalignment can cause toe wear on
both the front and rear tires by creating a steering pull to one side.
Unlike front toe which is self-centering because of the steering linkage,
a difference in rear toe angles side-to-side creates something called
a "thrust angle".
The result is the same as rear axle misalignment that causes the vehicle
to pull or lead to one side.
The next most important wheel alignment angle is camber. Camber refers to the tilt of the wheels as viewed from the front or the rear. Camber is the inward (negative) or outward (positive) tilt of the wheels. It is usually measured in degrees.
If camber is out of specs, a tire will wear unevenly on one shoulder and the vehicle may pull toward the side with the most camber.
Keep in mind that camber applies to both front and rear wheels, though only vehicles with independent rear suspensions typically have rear camber alignment specifications. Most rear-wheel drive cars and trucks with solid axles do not have rear camber specifications because there's no way to change it (even so, a bent rear axle can cause a camber problem!).
Excessive camber can be caused by bent or worn parts. If any of these parts are replaced, camber must be checked and adjusted as needed after the parts have been installed.
The third most important wheel alignment angle is caster, which is the forward (negative) or rearward (positive) tilt of the steering axix as viewed from the side. Caster is usually measured in degrees, and only applies to the front wheels because they are the only ones that steer (usually).
Caster is an angle that doesn't affect tire wear directly. It's greatest effect is on steering stability, steering effort and steering return. So it is often the most ignored angle.
If theres is too much difference in caster side-to-side, it can cause a vehicle to drift or pull to one side. Some alignment specs call for a slight difference in caster to compensate for road crown. As a rule, caster should usually be within half a degree side-to-side.
The same kind of problems that can cause camber misalignment can cause caster misalignment: bent or worn parts. So if any parts are replaced, caster should be checked and readjusted as necessary after the parts have been installed.
CHECKING WHEEL ALIGNMENT
The only way to make sure the wheels aree properly aligned is to check the wheel alignment angles periodically. Once set properly, wheel alignment should not change much unless parts become worn or damaged. Likewise, it makes no sense to attempt to realign the wheels until worn or damaged parts have been replaced. Worn parts will not hold an accurate alignment because they have too much play. There's also the danger that a component failure could result in the collapse of the suspension and/or loss of steering control.
Alignment Plus recommends an annual alignment check, or, have the wheel alignment checked whever the tires are replaced. Even new vehicles can benefit from an alignment check if the wheels were not properly adjusted at the factory. Some factory specifications allow a very wide range of settings, which may result in less than ideal tire wear and handling characteristics.
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