For most drivers, the issue of the geometry of the suspension seems simple and easy. After all, it is enough to go to the workshop, to "set to convergence" and you're done. Anyway, this problem, even when it is, many consider it insignificant, downright irrelevant, because and before
regulation, the car somehow drives. Meanwhile, the geometry of the suspension is a whole set of issues, which are far more complicated than car users think.
In general, the geometry of the vehicle suspension affects the stability of the movement, steerability and the method of transferring forces between the tires and the ground. An analysis of the issue will show, that the wheels should be perpendicular to the ground, and their plane of rotation parallel to the longitudinal axis of the car. And actually, it should be, as long as the suspension and body (rama) would be absolutely stiff, the cars would only run in a straight line, even surface, and there would be no lateral or longitudinal forces between the tires and the ground. In reality, however, the car is subject to various extortions, resulting from driving dynamics, both in straight lines and in curves, and what's more, the additional inputs are generated by the road roughness. To maintain driving comfort, and also keep (in real road conditions) contact of all wheels with the surface, vehicle suspensions have considerable working strokes and are very flexible. The attachment points for the individual moving parts are not rigid, and the body itself does not have perfect stiffness. So what do designers strive for?? Regardless of the construction of a specific suspension, the following effects should be obtained:
In rectilinear motion, the most important thing is, for the least resistance to motion, as well as driving stability, that the planes of rotation of the wheels are parallel to the longitudinal axis of the vehicle. In practice, this requirement is statistical in nature – this parallelism should be achieved as often as possible, under average operating conditions, including acceleration, braking and different loads on the individual wheels.
Moving in an arc, performed at a low speed, this is what is being done, that each wheel can roll freely around its circumference, resulting from the turning radius of the entire car. It is obvious, that the steering angle of the steered wheels on one axle must be different and be compatible with the track of the axles and wheels. The correct geometry of the steering system components is responsible for these phenomena.
In high-speed arc motion, it is essential, to be modern, wide radial tire, contact with the ground invariably with the entire tread width, irrespective of the momentary changes in vehicle suspension deflection and camber. The ideal would be to maintain this condition for all four wheels of the vehicle. In practice, however, the loaded outer wheels are more important.
The geometry of the steered axle should stabilize the vehicle movement when driving straight ahead, and the self-return of the steering wheel to the neutral position at the end of a turn