See Figures 1 and 2
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.
See Figure 3
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. On all vehicles covered by this information, caster is fixed by body geometry and it is not adjustable.
See Figure 4