If wheels are properly aligned, the steering wheel will tend to stay in a straight-ahead position on straight, level roads. Similarly, little effort should be needed to turn the vehicle into curves.
Caster is the angle between the steering axis centerline, and a vertical line through the center of the wheel. Backward tilt from the vertical line is positive caster. Forward tilt is negative caster.
Viewed from vehicle front, camber is the angle of tilt of the wheel from the vertical. A wheel leaning away from the vehicle at the top has positive camber. Leaning towards the vehicle, it has negative camber.
The effect of scrub radius is to provide a turning moment which attempts to turn the wheel away from the central position, when the vehicle is in motion.
As the wheel assembly swivels, it turns around the steering axis, on a line drawn through the upper and lower pivot points of the suspension assembly. Seen from the front of the car, it tilts inward.
Toe angles ensure that wheels are in line with the direction of travel. In the straight-ahead position, the wheels may have toe-in or toe-out, depending on manufacturer's specifications.
The thrust angle refers to all four wheels and their relationship to each other and to an imaginary centerline that runs from each pair of wheels down the center of the vehicle. The term 'thrust line' refers to the direction in which the rear wheels are pointing.
