Alignment

Tires should be checked monthly for signs of irregular wear in both tread and shoulder areas. Irregular wear indicates the need for a wheel alignment or suspension repairs. Also, when a replacement set of tires is fitted to a car, a wheel alignment is mandatory. Cars with four wheel independent suspension systems or cars with four wheel steering require four wheel alignment.

The three elements involved in wheel alignment are angles referred to as caster, camber and toe. Each affects the vehicle's performance.

Caster is the angle between a vertical line and a line drawn through the center of the ball joints (steering axis) when the vehicle is viewed from the side.

Positive Caster

Negative Caster

Caster is called positive when the steering axis tilts toward the rear of the vehicle at the upper steering pivot. Positive caster helps in maintaining directional control of a vehicle, tends to return the vehicle to a straight ahead position when cornering, and helps compensate for the crown on a road. Most cars are engineered with positive caster.

Improper caster can cause hard steering, increased road shock, reduced straight line stability and cause the vehicle pull to one side or the other.

Camber is the angle between a perpendicular line and a line drawn through the centerline of the tire when the vehicle is viewed from the front.

Negative and Positive Camber

Camber is called positive when the tops of the tires tilt away from each other. Camber helps distribute the vehicle's weight across the tire contact patch during cornering for reduced tread wear and is used to fine tune a vehicle's handling characteristics.

Incorrect camber causes uneven tire wear, poor steering and vehicle stability, and vehicle pull.

Toe refers to the angle between a line through the center of a vehicle and lines drawn through the centerlines of the tires when the vehicle is viewed from above.

Toe-In and Toe-Out

When the tires are closer together at the front than at the rear, the condition is called toe-in. When the tires are closer together at the rear than at the front, the condition is toe-out.

The toe adjustment is the most critical to tire wear. Incorrect toe results in rapid and uneven wear.

When a manufacturer designs a car, engineers select these elements (angles) and establish them as specifications for the best overall vehicle handling performance. Failure to properly align a car's wheels can result in excessive tire wear, excessive fuel consumption and unsafe handling.

Source: Dunlop Tire Corporation

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