Chassis explained

Technology has its traditions, too

Fundamental principles of chassis technology date back to the age of the stagecoach. At that time, the chassis proper – that is the wheels, steering and suspension – was separate from the body of the carriage (the “carrosserie”). In the age of the automobile, demands on chassis technology have multiplied. In addition to passenger comfort, the chassis is still responsible for bringing the driving torque to bear on the road surface, supporting the vehicle mass, keeping the vehicle on the desired bearing, and compensating for external disturbance variables such as bumps or wind. Car chassis therefore bear a central responsibility for driving comfort, dynamics and safety – what ultimately makes driving a car an enjoyable and safe experience.

An eye of the needle

Contact patch - an eye of the needle

All forces are directed through four surfaces, each around the size of a beer mat – the area of each wheel that touches the road surface. This is the so-called “contact patch.” Making the best possible use of these very limited contact surfaces is a prime task of the chassis. If one or more wheels lose road contact even briefly, no steering, braking or driving forces can be transferred through it. Static and dynamic forces work through the contact patch superimposed in all three spatial planes: Vertical dynamics work upwards from below, or vice versa, and are felt when driving over a rough surface. Lateral dynamics work laterally across the vehicle, for instance when cornering. Longitudinal dynamics work from front to rear, and vice versa, for instance during acceleration and braking.

To enable the most comfortable, safest and dynamic drive possible in all conceivable driving situations despite these forces, various elements are included in the chassis – that whole ensemble, so complex to the lay eye, of longitudinal and transverse control arms, wheel carriers, rubber mounts, ball joints and stabilizers. Beside this wheel suspension proper, important parts are also played by the shock absorbers, springs and tires. Also worth mentioning at this point: All of this is purely mechanical. No electronic aids are part of the equation yet. That is because driving qualities and active driving safety can be further improved by regulating systems in steering (power steering and active steering) and braking systems (ABS and ESP), variable dampers (such as CDC), regulated suspension struts or stabilizers, and traction slip regulation.

Visions of a simple chassis

What the layman might unlovingly refer to as “the rods” is really an ensemble that is tuned for all driving situations. The rule of thumb is the more “rods” (that is, suspension arms, supports and stabilizers) are active, the more precisely the various, sometimes contradictory demands of the situation can be met – but also the more space the chassis will take up and, under certain circumstances, the heavier it will be. So today, engineers are pursuing a different path: that of functional integration. Moreover, they are seeking out new materials. Lightweight construction in the chassis also means designing a less complex chassis structure. But nevertheless chassis construction will always be complicated. The question is only how visible that complexity is from outside. In any case, one thing is certain: the stagecoach is history.