DIY Network

Tires and Alignment Learn how proper wheel alignment can increase the longevity of your tires. From "Car Care & Repair" episode CCR-116

Maintaining the proper wheel alignment on your vehicle is critical for ensuring optimum handling, and it will also increase the longevity of your tires. In fact, misalignment and improper inflation are probably the two biggest causes for tires wearing out prematurely.

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Symptoms of a vehicle that's out of alignment include vibration, shimmy or a tendency for the vehicle to "wander," or pull to one side when driven at highway speeds. If you're driving on the highway and you loosen your grip from the steering wheel for just a second, an improperly aligned vehicle is likely to start edging to one side or the other rather than maintaining a straight line. Causes for misalignment include aggressive cornering, hard braking or bumping a curb. Alignment involves adjusting the wheels to certain specifications so they track in a straight line. Frequently mechanics will refer to a "front-end alignment" since the front wheels are more often the ones that become misaligned.

	Figure A
	Figure B

Driving on a vehicle that is out of alignment will cause tires to wear unevenly, usually on the outer edges (figure A). To avoid damaging your tires, and to make sure the alignment problem doesn't continue getting worse, it's important to correct the situation as soon as possible. When your mechanic performs an alignment, several factors are checked.

Camber refers to the inward or outward tilt of the wheels (illustrated with a bicycle wheel in figure B). If the tops of the wheels angle in toward the vehicle, this is referred to as negative camber. If the tops angle away from the vehicle, it is a positive camber. When properly adjusted, the camber angle keeps the outside tires flat and stable on the ground during a turn. Improperly adjusted camber will result in improper handling and tires that wear out prematurely.

Caster refers to the angle of the vertical axis of the wheel in relation to the steering connection. A higher caster angle gives greater stability at high speeds, but steering may be more difficult at lower speeds. A lower caster angle results in more ease in steering, but the vehicle may wander at higher speeds. Caster is adjusted according to factory specifications on individual vehicles to arrive at the optimum balance -- achieving stability and control at both high and low speeds. Properly adjusted caster allows the wheels to track in a straight line and prevents shimmy.

Figure C

Toe refers to the front end of the wheel. "Toe-in" is a condition in which the front ends of two wheels on the same axle are angled slightly inward so that they are closer together than the heel ends. "Toe-out" refers to the opposite condition -- the toes of two wheels are angled slightly outward, so that they are farther apart than the heels. Severe toe-in or toe-out causes uneven and excessive wear so that one side of the tread wears out more quickly than the other (figure C).

Factory specifications for camber, caster and toe are established for every vehicle and should be followed exactly. Improper alignment not only causes poor handling and premature tread wear, it also reduces fuel efficiency.

RESOURCES :

Tires, Suspension and Handling
ISBN: 1560918314
Author: John C. Dixon
(Society of Automotive Engineers