The new SLK 55 AMG: Top marks in all disciplines
Nov 18, 2011
Chassis and braking system: Driving dynamics at the highest level
  • Specific AMG sports suspension with aluminium hub carriers
  • Direct-Steer system enhances agility and comfort
  • AMG high-performance braking system and Torque Vectoring Brake
  • 3-stage ESP® with customised control strategy
  • Optional AMG Handling package available
To ensure optimum wheel control, the SLK 55 AMG features three-link front suspension and multi-link independent rear suspension. Forged aluminium hub carriers reduce the unsprung masses, which benefits both the road feel and response of the spring assemblies. The AMG sports suspension, specifically tuned for high performance, comprises independent suspension struts with stiffer spring/damper tuning. In combination with all-round stabilisers with a larger diameter, more rigid torque strut bearings on the front axle as well as a more negative camber on the rear axle, the SLK 55 AMG impresses with neutral understeer/oversteer characteristics, high cornering speeds and a low body roll in fast S-shaped bends.
Yet the top-of-the-range SLK model from AMG boasts not only a highly dynamic driving style but also comfortable cruising thanks to the comfort on long journeys which is characteristic of a Mercedes. The AMG light-alloy wheels measuring 8 x 18 (front) and 9 x 18 (rear) are fitted with 235/40 R 18 and 255/35 R 18-sized wide-base tyres.
Innovative: Torque Vectoring Brake and Direct-Steer system
To increase agility and lateral dynamics even further, the SLK 55 AMG comes fitted with the Torque Vectoring Brake and Direct-Steer system as standard. The Torque Vectoring Brake is able to detect a tendency to understeer and generates a defined rotational movement of the vehicle about the vertical axis. This is made possible thanks to targeted braking intervention, within fractions of a second, by the Electronic Stability Program ESP® on the inside rear wheel when cornering. This results in the SLK 55 AMG steering into the bend precisely and under full control, without any loss of handling dynamics. This system is complemented perfectly by the AMG Direct-Steer system: compared with standard steering, it increases handling and agility, enhances safety at higher speeds, such as on motorways, thanks to a greater steering effort being required, and at the same time also reduces the physical effort required when parking.
The ratio is indirect when the steering is centred, which ensures good straight-line stability and therefore a high level of safety. In contrast to other variable steering systems, the ratio of the Direct-Steer system increases rapidly after a steering angle of 5 degrees, becoming extremely direct from a steering angle of just 100 degrees. Only relatively small steering movements are then needed to make course corrections. The increase in driving dynamics is also aided by an increased yaw rate (steering response) at low to medium speeds, as this augments the effect of the steering movement. At high speeds this increase in yaw rate is small, which means that the car responds safely and predictably to steering movements.
Despite its remarkable effect, the key component of the Direct-Steer system is a tried-and-tested steering rack. Its secret lies in the teeth cut into it. In the mid-area these are slightly wave-shaped, with varying flank profiles. To both sides the teeth are spaced at varying distances apart. The change in steering ratio is therefore produced by purely mechanical means. With this ingenious solution, Mercedes engineers have been able to dispense with the elaborate actuators and complex sensor systems used by other variable steering systems. The advantages of the Direct-Steer system therefore include very low susceptibility to faults and low weight. Moreover, the system always responds predictably and in the same way at each steering angle, while other variable steering systems sometimes require rapid adaptation by the driver in rapidly changing situations.
Power steering pump reduces consumption
A newly developed power steering pump helps to reduce fuel consumption. The power assistance for the steering only requires energy when the driver is actually steering. In addition, the AMG Direct-Steer system has a parameter function adapted to match the characteristics of the AMG sports suspension. This results in optimum response from the central position, outstanding road feel and dynamic handling in all driving situations.
3-stage ESP® system with "SPORT Handling Mode"
A special feature exclusive to AMG is the 3-stage ESP® system. It enables individual control strategies to be selected at the touch of a button: using the ESP® button in the centre console, the driver is able to choose between "ESP ON", "SPORT Handling Mode" and "ESP OFF". The currently active mode is shown in the display of the AMG instrument cluster. In "ESP ON" mode, braking intervention on one or more wheels and a reduction in engine torque occur if the car starts to become unstable.
Briefly pressing the ESP® key activates "SPORT Handling Mode". By means of over/understeer intervention accompanied by engine torque adjustment, this mode allows even more dynamic handling manoeuvres such as the appropriate drift angles. All the functions of ESP® are available as soon as the brake pedal is depressed.
Sustained pressure on the ESP® key activates "ESP OFF". In this case there is no dynamic control intervention whatsoever, and the engine torque is no longer reduced. "ESP OFF" should only be used by highly experienced drivers on closed racetracks. In this mode too, all the functions of ESP® are available as soon as the brake pedal is depressed. In all three ESP® modes the traction logic of the acceleration skid control (ASR) is active. As soon as a drive wheel begins to spin, traction is significantly improved by specific braking intervention.
Powerful AMG high-performance braking system
The AMG high-performance brake system is characterised by outstanding responsiveness, short stopping distances and excellent fatigue strength. The ventilated and perforated brake discs on all wheels are decelerated by means of
4-piston fixed callipers (front) and 1-piston floating callipers (rear), respectively. A new addition is the electrically operated parking brake: its switch is located in the dashboard, under the rotary light switch. Pressing this engages the electric parking brake, and pulling releases it. The brake is also released automatically as soon as the engine is running, the transmission is in the D or R position, the driver has a fastened seat belt and the accelerator is operated.
Also included as standard equipment is ADAPTIVE BRAKE. It comprises ABS, the acceleration skid control system ASR and also active yaw control (GMR). In addition, it features the following functions:
  • it supports the driver when moving off uphill, by preventing the vehicle from unintentionally rolling back;
  • it also keeps the vehicle stationary without having to keep the brakes applied continuously - for example when waiting at traffic lights (HOLD function);
  • as soon as the driver abruptly steps off the accelerator, it brings the brake pads into light contact with the brake discs as a precautionary measure, so that the necessary braking pressure can be attained quicker in the possible event of emergency braking;
  • in wet conditions it applies light brake contact, without the driver even noticing, to dry the brake discs.
The ADAPTIVE BRAKE works in conjunction with the equally adaptive brake light. In emergency braking situations, it warns vehicles behind with flashing LED brake lights.
Overview of brake data:
Front axle
Rear axle
Brake disk
Diameter Thickness Brake calliper
Cast aluminium, ventilated, perforated
360 mm
36 mm
4-piston fixed calliper
Cast aluminium, ventilated, perforated
330 mm
22 mm
1-piston floating calliper
Optional AMG Handling package for even greater driving dynamics
The new AMG Handling package available for the first time as an optional extra enhances the vehicle's sportiness even further. In technical terms, it comprises an AMG Performance suspension with approximately 30 percent stiffer tuning, an AMG rear axle differential lock with setup tuned specifically to the vehicle, and also composite brake discs on the front axle. In the interior, the AMG Handling package differs from the standard appointments fitted to the SLK 55 AMG with the addition of a three-spoke AMG Performance steering wheel finished in nappa leather with Alcantara® inserts in the grip areas.
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