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Alignment

Alignment is a term that covers a large number of potential problems. Alignment refers to the relation of each of the wheels and tires to the road.

The tires of an aligned vehicle offer the least amount of resistence to its forward motion, provide the best steering/turning control, and cause the least amount of wear to the tires. To begin, the wheels must be balanced, correctly oriented vertically called Camber, horizontally called Toe, and directionally stable called Caster, as well as being firmly supported by components like wheel bearings, tie-rod ends, balljoints that are not excessively worn or damaged.

Toe

Toe-in/out or Camber misalignment places most of the work on one side of the tire and is typically the cause of one-sided wear.

Toe In
This condition occurs when the front edge of the tires are closer together than the rear edges. Toe-in counteracts the tendency of the front wheels (of a rear wheel drive car) to toe-out under power. When a car is driven at highway speeds, toe-in is opened up from the force of the road surface and the wheels roll straight.

Toe Out
This condition occurs when the rear edge of the tires are closer together than the front edges. Some toe-out is necessary for all cars when turning, because the inner wheel must turn at a sharper angle than the outer wheel.

Camber

Camber is the tilt of the top of a wheel inward (negative camber) or outward (positive camber). Proper Camber, along with correct Caster, assures that the tread is as flat against the road as possible under all driving conditions.

Negative Camber
Excessive negative Camber causes wear on the inside edge of the tire.

Positive Camber
Excessive positive Camber causes wear on the outside edge of the tire.

Caster

This is the forward (negative) or rearward (positive) tilt of the spindle steering axis on a car or the kingpin on a truck. Correct caster on a vehicle is never perfectly vertical but is always set on a slight angle. A bicycle provides a good example of caster. The front fork on which the front wheel is mounted is almost always tilted back, giving the front wheel positive caster. This allows the rider to ride with no hands. If you turn the wheel around the directional ability is diminished, if you let go now you may suffer a crash.

The basic purpose of caster is to maintain directional control, give more on-center "feel" to steering, and return the vehicle to a straight ahead position when coming out of a turn. Insufficient caster causes wander, road shock, and a light feeling in the steering. Excessive positive caster can cause hard steering, shimmy, and tire wear in extreme cases. Unequal caster causes the vehicle to pull or lead toward the side having the least positive caster.

When caster is out of manufacturer's specification range, tire wear may occur as a result of incorrect camber on turns. Loose or worn steering or suspension parts that would produce an incorrect caster angle would also affect camber and toe, which would also cause tire wear.

The Mechanics Insight is a monthly newsletter that includes comment on the nature and business of the auto world, and also includes minor diagnosis for various subjects to the subscribers of the newsletter, but will not be included on theWeb page.

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