Steering a motor vehicle is possible because of a complex arrangement of pivots and linkages which are supported by the vehicle frame, or uni-body, and connect to the wheels. Steering motion to the wheels is controlled by the wheels turning about fixed pivots anchored to the vehicle frame. The relationship of the wheels to the frame, or uni-body is determined by the suspension system. The steering system is dependent on the front and rear suspensions and vehicle frame to function correctly. Actually, all of these groups are interdependent in that a change in one can affect the others and the steering characteristics of the vehicle. We refer to them together as the "Chassis System". Auto manufacturers attempt to put the wheels of the vehicle in the best possible position to permit free- rolling movement with a minimum amount of scuff, or tire wear.

Wheel alignment service is most often referred to as “Front End Alignment”. A request for this service is usually the result of unusual tire wear or a handling problem. Problems with alignment occur more often on the front axle; as the steering axle usually has more pivots. It is also subjected to more stress because of its turning abilities and the added weight of the engine, which the suspension must support. The rear suspension may be a solid axle, stamped axle or independent suspension. The rear usually has less load and stress applied to it than the front, therefore service requirements are less.

An alignment specialist knows that he must think of alignment as a system rather than a front end adjustment. Because the frame, steering and suspension systems are interdependent, they all will affect handling and must be checked before any adjustments are made. Some amount of adjustment is often necessary because of road conditions, spring fatigue or varying loads. Worn parts should be replaced prior to alignment.

 
A vehicle’s chassis is made up of three parts: 

The suspension system, which is responsible for keeping the wheels firmly in contact with the road, while letting them move to cushion bumps or road shock.

The steering system, which keeps the wheels and tires pointed in the right direction and works with the suspension system to steer the wheels with precise control.

The frame, which, as the name implies, serves as the framework that holds the vehicle together.

How they work together: The steering and suspension systems have different functions. Steering is performed by the driver to direct the vehicle, while the suspension is a structural arrangement at each of the four wheels to support the vehicle and provide a smooth, comfortable ride.

The suspension system includes springs, shock absorbers, control arms, bushings and ball joints, which keep the wheels in correct position while allowing up-and-down movement. The steering system is made up of a steering wheel, steering column, gear box (or rack and pinion) and tie rods, which connect the steering wheel to the road wheels. Steering and suspension systems vary in appearance and design, due to space, weight, cost and design considerations. 

Points where one part of the system connects to another are known as pivots. All steering and suspension systems have pivot points — from the vehicle frame to the tires — that work together and depend on each other, like the links in a chain. They are affected by the same forces and wear factors. A change in one component can affect others, and wear in one component can cause problems further down the chain, causing problems in one or both systems.