Ever wondered why we call suspension on a car "suspension"? Here's the answer:
Although wheeled transport was probably introduced around 3500 B.C., the vehicles were mostly load carriers which did not require a high degree of comfort, and when people wanted to reduce the shaking, they thought in terms of smoothing the road surface rather than developing the carriage.
About the middle of the 16th century, people began to work on the insulation of the carriage from the road wheels. The first known system involved a chassis that looked like an upturned table, with the carriage body slung by leather straps from the tops of the legs. This was not a springing system as it only allowed the body and the wheels to move seperately. This formed the basis for springing being called the "suspension".
The first springing development was the replacement in 1665 of the table legs by big C-shaped springs, a form of insulation that can still be seen on children's prams. But this system had disadvantages in allowing forward and backward sway and giving a high centre of gravity and a high roll axis. They also used to spring only the body, leaving the heavy chassis unsprung.
By the time that powered vehicles were developing, the springs had changed to an elliptical shape and were bolted between the axle and the chassis. The primary function of suspension at this time was to allow the four wheels to keep contact at all time with an uneven road surface and any increase in the comfort of the passengers was a bonus.
The need of a compromise between a suspension system keeping the wheels on the ground, and one that provides maximum insulation from the road shock for the passengers has always been a problem and is still unsolved today(Although 'adaptive suspension' is a great help). The strength, or rate, of the springs between the wheels and the body cannot instantly be altered according to the kind of bump the wheel is about to meet.
When a wheel hits a bump, it moves upward from the surface and gains momentum in that direction. If the wheel is unsprung, all the energy is transfered to the body which moves in the same way. And the gravity which is the only force acting on this movement will eventually bring it back sharply to the ground. By putting a spring between the wheel and the chassis, much of the energy of the moving wheel is transferred to the spring instead of being transferred to the chassis which therefore moves upwards through a smaller distance than the wheel.The lighter the wheel and the other pieces connected to it, the smaller is the total energy involved because this amount of energy depends on the mass involved.
A low spring rate permits a large wheel movement and so a low chassis movement but it must be strong enough to bear the chassis properly. So although soft springs should give the greatest comfort, they won't do much good if the chassis squashes them totally. On the other hand, a stiff spring that doesn't deflect much under the chassis does not offer much comfort and gives a hard ride.
The problem with springs is that they store the energy without dissipating it and so tends to release it by moving the wheel downwards hence a vibration of the spring at its natural frequency. It is possible for the vertical accelerations of the wheel to coincide with the natural frequency of the springs and in this condition, the movement can become large enough to lift the wheel off the road and therefore losing grip and traction, this is very undesirable. To fight against this phenomenon, engineers designed a damping device sometimes known as a shock absorber (although this description has also been used for systems that combine dampers and springs together). Its function is to dissipate (generally by friction of fluid through small holes or valves within the damper), the energy stored in the springs by providing a damping force proportional to the relative velocity between the two moving systems.
Many companies have expended massive efforts and resources to develop the best systems available for car manufacturers and for aftermarket applications. Some of the better known suspension companies are Koni, KW, and Bilstein.
But the suspension is not only made of springs and dampers, the tyres and wheels can also be considered as springs as they absorb the small irregularities from the road surface.
Some notes on suspension setup:
- Toe In gives lively steering.
- Toe Out gives heavy steering.