A car alignment is actually an elaborate process that brings the car's suspension into its proper configuration, positioning and adjusting components so that wheels are aligned with one another and the road surface. The alignment should be performed by an experienced mechanic, who uses an alignment machine.
Newer alignment machines feature clamplike devices that are attached to the wheels of the car (which is raised up in the air) and that link to a computer that helps make precise measurements. The mechanic will also take this opportunity to make sure that no suspension components are excessively worn or broken.
An alignment essentially requires squaring a car's wheels and axles with each other so that they're moving in the same direction. The mechanic adjusts the various suspension angles -- known as toe, thrust, camber and caster -- that influence tire movement and position. The technician will also ensure that the steering wheel is centered.
Each car's manufacturer designates standard angles for the alignment, specified in degrees. If you're a driver of a high-performance car or sports car, your mechanic may be able to align your suspension to improve handling and tire performance, but such an alignment still may lead to uneven tire wear.
The type of alignment you receive will depend on your car's suspension. A four-wheel alignment is reserved for all-wheel drive vehicles or front-wheel drive vehicles with independent or adjustable rear suspensions. In this case, both axles have to be properly aligned so that all four wheels align in a rectangle, parallel to one another and perpendicular to the ground.
If you don't have a four-wheel or all-wheel drive vehicle, your car will likely only require a front-end alignment, in which only the front-axle components are adjusted, or a thrust-angle alignment. Thrust angle refers to the angle that a car's rear wheels point relative to the car's center. In such an alignment, the rear wheels and axle are realigned so as to be parallel with the front axle and perpendicular to the center line of the car.
After the alignment is complete, it's appropriate to ask for a printout -- which many mechanics now provide -- that shows before and after images of the suspension alignment.