In relation to the car, a wheel can move in three directions and also rotate in three directions. Of the movements, only one is desired: the vertical. And of the twists we only want to be able to steer, that is to say only rotate about the vertical axis. That sounds complicated, but is it?
The wheel can act in three directions: parallel to the direction of travel, transverse to the direction of travel and vertical. In the same directions, there are also twists, twists due to the forces, or moments. The only linear movement that is desired is the vertical, we are talking about spring and spring. In the other two directions, we want the wheel to remain in a fixed position relative to the car. This means that longitudinal drive, braking and rolling resistance forces must be coped with. In the transverse direction, these are forces that occur because we round a bend, drive on an oblique plane or perhaps suffer from crosswind. To keep the wheel in place, the suspension must be able to provide counterforce in all three directions. This requires, among other things, a smart arrangement of wishbones that must allow springing in.
If all forces and counter forces all intervene at the same point, the story would end here. However, that is not the case. To start with, the pivot points of the pivots are not exactly in the middle of the tire. The longitudinal forces therefore provide a moment around those pivot points. This moment is counteracted by the tie rods. Because these forces in the track rods are equal to the left and right when driving straight ahead, this does not bother us further. The moments as a result of braking and driving can be absorbed by the wishbones, while the moments caused by the transverse forces at the front can be partly absorbed by the knuckles, but also partly eliminated by the trailing angle (caster) of the knuckles. tie rods.
Naturally, there is a wide variety of suspension structures. But whether it’s a McPherson strut, a multi-link construction, a torsion or rigid axle, they all have to resist the same forces and moments.