All wheels of a vehicle must be correctly positioned, with the vehicle and with each other, for the vehicle to drive and steer properly.
A driver should not need to keep manipulating the steering wheel to maintain the vehicle in a straight-ahead position on straight, level roads.
Similarly, little effort should be needed to turn the vehicle into curves, or to let it return to the straight-ahead position, when the curve has been negotiated.
Wheels are installed on the suspension units at certain angles, to provide for these factors. These angles, taken together, are called wheel alignment.
The factors that affect wheel alignment are