If the tires are worn unevenly, if the vehicle is not stable on the highway or if the handling seems uneven in spirited driving, wheel alignment should be checked. If an alignment problem is suspected, first check tire inflation and look for other possible causes such as worn suspension and steering components, accident damage or unmatched tires. Repairs may be necessary before the wheels can be properly aligned. Wheel alignment requires sophisticated equipment and can only be performed at a properly equipped shop.
Wheel alignment is defined by three different adjustments in three planes. Looking at the vehicle from the side, caster angle describes the steering axis rather than a wheel angle. The steering knuckle is attached to the strut at the top and the control arm at the bottom. The wheel pivots around the line between these points to steer the vehicle. When the upper point is tilted back, this is described as positive caster. Having a positive caster tends to make the wheels self-centering, increasing directional stability. Excessive positive caster makes the wheels hard to steer, while an uneven caster will cause a pull to one side.
Looking at the wheels from the front of the vehicle, camber adjustment is the tilt of the wheel. When the wheel is tilted in at the top, this is negative camber. In a turn, a slight amount of negative camber helps maximize contact of the outside tire with the road. Too much negative camber makes the vehicle unstable in a straight line.
Looking down at the wheels from above the vehicle, toe alignment is the distance between the front of the wheels relative to the distance between the back of the wheels. If the wheels are closer at the front, they are said to be toed-in or to have a negative toe. A small amount of negative toe enhances directional stability and provides a smoother ride on the highway. On most front wheel drive vehicles, standard toe adjustment is either zero or slightly positive. When power is applied to the front wheels, they tend to toe-in naturally.