Suspensions usually have a clear task: the body should float on them as much as possible – and swing little. Manufacturers solve this with various technical approaches. How does car suspension work? Our guide will outline how to understand car suspension systems.
Understand car suspension systems: the types
To understand car suspension systems, it’s handy to first look at the different types — and there are many. Steel springs, adaptive dampers or air springs: When browsing car brochures, one reads very different terms in connection with suspension/chassis. The choice, it’s great. But what is behind the different systems?
Driving sensation and handling of a car are largely determined by the chassis. Among other things, springs and dampers are responsible for this.
In most cars, steel springs and conventional shock absorbers with a fixed damping are installed in the wheel boxes, which compensate for the dynamic wheel load fluctuations. Steel spring suspensions include coiled spring springs made of spring steel. The spring length determines the vehicle height, the spring hardness determines the comfort and the driving behavior. They are compact – and cheap.
Adaptive dampers for different driving situations
Adaptive dampers, on the other hand, offer a wide spread for different driving situations thanks to adjustable damper valves. “They can be selected in several basic chassis settings, such as a comfort and a sports setting,” says Karsten Schebsdat, Head of Driving Dynamics, Steering and Control Systems at Volkswagen.
In general, VW installs a steel chassis in its cars, only the models of the Touareg off-road vehicle optionally rely on air springs in combination with controlled dampers.
Air springs require a control unit
In the case of air springs, the spring volume can be adjusted and thus the stand height and stiffness. The basic stiffness can be softer with air springs, the driving comfort is higher. However, air springs require a control unit and an air compressor.
“An air suspension is more complex, requires more effort, more space and costs more. We therefore do not offer them for compact and small cars, but in the upper class,” says Schebsdat.
Choice of axles
Not the only choice when buying a car. In the Golf, Volkswagen uses a more complex four-wheel drive axle with an output of 96 kW/130 hp instead of a simple composite steering axle. “This improves driving stability, steering precision and driving comfort,” Schebsdat says.
Motorists also feel the difference between conventional chassis with steel springs and simply controlled dampers and a chassis with electrically adjustable damping directly. In the VW chassis called the DCC, drivers switch between the steps at the touch of a button. The chassis should become more comfortable or even tighter, more precise and more direct, depending on your choice. For many VW models, however, the DCC chassis is a special feature.
The differences between steel and air
Rüdiger Rutz, responsible for testing various SUV models at Mercedes-Benz, sees fundamental differences between the different types of chassis. “The biggest one is between the classic steel spring and the air suspension,” he says.
Regardless of the type, they carry the body work of the vehicle. However, the air suspension reacts variably to the payload, keeps the vehicle level constant and thus improves the driving behaviour. In the case of steel springs, the driving behaviour changes with higher payload, because the vehicle is more absorbed.
“That doesn’t mean that steel springs are bad. A well-made steel suspension offers sufficient comfort, sportiness and safety, depending on the type of vehicle and the tuning,” says Rutz. “Only with a high load can it reach its limits and is therefore less variable.” The advantage of the conventional steel spring lies in its price: it is significantly cheaper than the other variants.
More comfort thanks to air suspension
One advantage of air suspension is that it automatically balances the vehicle level during loading. At Mercedes, therefore, station wagons such as the E-Class are equipped with a standard air suspension on the rear axle. For SUVs, it pumps up the body in the terrain for more ground clearance and lowers it when driving on the highway for better wind slip-up and lower consumption.
Rutz says: “The air suspension is more variable for different driving situations and also offers a more comfortable and softer basic setting than a steel suspension”.
Systems such as Mercedes’ E-Active Body Control can read the road in a way and adjust the chassis to the unevenness in advance. Drivers are supposed to glide across the road with their cars more smoothly. The downside: The system costs extra.
The compromise: steel adjustment suspension
A compromise between the two variants is the steel adjustment suspension. Steel springs are combined with an adjustable damper to allow a wider range between comfort and sport than with a conventional chassis. Depending on the choice of the driving program, the damper characteristic curve changes at the push of a button.
Drivers can adjust adjustable or adaptive dampers or the suspension adapts itself to the conditions. Adaptive suspensions have advantages in terms of comfort in normal driving situations and are significantly cheaper than air suspensions. Adaptive dampers are standard equipment at Mercedes, for example.
Active or semi-active chassis
Christoph Elbers, head of passenger car chassis technology at automotive supplier ZF, distinguishes between two types of adaptive chassis. According to its data, the semi-active switches back and forth between different damper characteristics more quickly and changes the corresponding damping force – and automatically, depending on the driving situation and control strategy.
With the active, adaptive chassis, the dampers can be additionally supported, so that in curves, for example, the inner-curve dampers absorb pressure, while the outer ones build up more pressure. “That’s how a car drives through the bend like a flying carpet,” says Elbers.
“Motorists can feel the difference between the different chassis, but usually this happens subconsciously. Then, if they just don’t feel the pothole on the road in their backs or their car drives through the bend without much inclination,” says Elbers. They don’t notice a big difference until they drive the same vehicle with a different chassis.