The new Mercedes-Benz SL 63 AMG: Chassis and braking system - Driving dynamics at the highest level

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High-performance drive and power transmission systems call for high-tech suspension and braking systems. In this area too the SL 63 AMG is able to fulfil all of the expectations which are made of it. The characteristic qualities already valued by customers in the preceding model – dynamic handling and high levels of agility, combined with the comfort on long journeys typical of Mercedes – have been optimised and refined even further by Mercedes-AMG in the new edition of the high-performance Roadster.

As with the body, the experts from Affalterbach also turned to aluminium for the AMG sports suspension too. The steering knuckles and spring links on the 4-link front axles are therefore also made of aluminium, as are virtually all of the suspension parts on the multi-link independent rear suspension. The integral support frame for the front-axle halves, steering gear and engine is also produced in aluminium. The result: the weight savings achieved compared with regular components made of steel help to reduce the unsprung masses, which in turn results in measurable and noticeable benefits in terms of the response of the spring and damper elements as well as the agility. Another significant highlight is that the SL 63 AMG has more negative camber on both axles as well as fully revised elastokinematics for a more direct driving sensation and higher lateral acceleration. Also contributing to this same effect is the track width, which is significantly wider than that of the preceding model (front axle is 52 mm wider, rear axle 50 mm wider).

Active Body Control optimised for even greater performance

Driving dynamics also feature as part of AMG's new design. The sports suspension based on Active Body Control (ABC) has come under the spotlight. During the development and testing phase, active suspension control was specially optimised in terms of cornering performance. Basically the ABC suspension all but entirely eliminates the body movements that occur when moving off, cornering on uneven road surfaces and braking. Bends are negotiated with far less roll; the body roll caused by fast evasive manoeuvring is effectively suppressed. The control elements of this system are the damper struts, in which a hydraulic servo cylinder is arranged in series with the steel spring. By retracting and extending, this cylinder actively adjusts the length of the spring and therefore the spring force of the damper strut. As a result, conventional torsion-bar stabilisers can be dispensed with on the front and rear axles.

High-performance control electronics in permanent dialogue with the engine and transmission control unit ensure that the forces of the four damper struts are adapted practically instantly. A new feature is the visual ABC display in the COMAND system menu: driver and front passenger can monitor the individual actions of the active suspension control on each of the wheels in real time.

Briefly pressing the suspension button designated with a shock absorber symbol in the AMG DRIVE UNIT changes the characteristics of the AMG sports suspension: the roll angle through fast corners is reduced further, the shock absorbers and springs also respond firmer to promote agility. In Sport mode, ABC automatically lowers the body continuously by up to 8 millimetres at speeds of between 65 and 100 km/h. In Comfort mode, lowering takes place between 140 and 170 km/h. The positive effects include reduced wind resistance and a lowering of the vehicle's centre of gravity. If more ground clearance is needed when driving on poor road surfaces or over ramps, the level of the vehicle can be raised by a maximum of 55 millimetres at speeds up to 30 km/h. 

Active Body Control also available as performance suspension

As an option, the AMG performance suspension is also available for the SL 63 AMG from the AMG Performance Studio. Damper characteristics can be made stiffer by up to 30 percent in both modes. This provides for even less body movement and is recommended when striving for high-speed laps on a closed-off racing circuit, for example.

Another notable feature of Active Body Control is the variable roll moment distribution between the front and rear axles, which the system carries out automatically according to the driving situation and speed. The computer uses various acceleration sensors to obtain information on the current driving situation and compares this data with those from the pressure sensors in the spring struts and the level sensors on the control arms. The system then computes the control signals that the servo-hydraulic valves at the front and rear axle transform into precisely metered flows of oil. In addition, the SL 63 AMG is fitted with hydraulic all-round self-levelling which helps to ensure a constant vehicle level irrespective of the load being carried.

AMG speed-sensitive sports steering with variable power assistance

One new development is the electromechanical AMG speed-sensitive sports steering: with its constant and direct ratio of 14:1, it enables a sporty response from the central position and supports the vehicle's largely linear understeer/ oversteer characteristics. The result is light-footed, agile cornering behaviour and clear feedback at critical limits.

And that is not all: for the first time, the top-of-the-range AMG model features power assistance which adapts according to the suspension mode. In "Comfort" mode, the AMG speed-sensitive sports steering responds comfortably, with a higher degree of steering assistance. In "Sport" mode on the other hand, the driver feels less steering assistance – which translates into an improved sense of road feel. This benefits both response and steering precision, particularly at high speeds and when adopting a sporty driving style.

New steering helps to save fuel

In addition to more precise steering and a more comfortable feel at the wheel, the new electric power steering offers a range of additional advantages. It makes an important contribution to efficiency, since the steering assist function only requires power when the driver actually steers. Compared with the previous model with regular hydraulic power steering, this enables savings of up to 0.3 litre/7 g CO2 per 100 km (NEDC combined) to be achieved.

Power assistance is also available when the engine is stationary, for example – whereby an algorithm ensures that the combustion engine is not prompted to start up in ECO start/stop mode when the driver is merely moving the steering wheel while the vehicle is at a standstill. The new steering system has also enabled implementation of the "Active Park Assist" automatic parking function and relieves the strain on the driver on road surfaces which slope away towards the kerb.

In the new steering system the steering gear and the supporting servo-motor form a single compact unit and are mounted on the integral support frame made of aluminium and positioned in front of the wheel's centre line. The high-performance control unit processes a variety of parameters captured by the ESP® control unit – including vehicle speed, steering angle, steering angle speed, lateral acceleration and also understeer/oversteer characteristics – and in a split second calculates the forces which the driver needs to input into the steering in different driving situations – from parking to high-speed motorway driving. Active damping enhances the feeling of safety when driving straight ahead at high speed.

3-stage ESP® system with "SPORT Handling" mode

As previously, the SL 63 AMG offers 3-stage ESP® as standard: the Electronic Stability Program supports three individual control strategies at the push of a button. The ESP® button in the AMG DRIVE UNIT allows the driver to choose between "ESP ON", "SPORT Handling" mode, and "ESP OFF" – with the currently active mode shown in the display of the AMG instrument cluster. In "ESP ON", the onset of handling instability leads to braking intervention at one or more of the wheels, accompanied by a reduction in engine torque.

Briefly pressing the ESP® button activates "SPORT Handling" mode. In this mode the braking intervention to counter oversteer or understeer, as well as the accompanying reduction in engine torque, allows a higher dynamic threshold and, for instance, corresponding drift angles – the driver benefits from significantly enhanced driving enjoyment. As soon as the driver operates the brake pedal, all of the normal ESP® functions are restored. Prolonged pressing of the ESP® button activates "ESP OFF". With this, the engine torque is no longer reduced to control the driving dynamics – and driving enjoyment is therefore increased even further. "ESP OFF" should only be used by experienced drivers on dedicated racetracks. In this mode too, all of the functions of ESP® are made available by operating the brake pedal.

The system's traction logic is active in all three ESP® modes. If one of the drive wheels starts to spin, specific brake pressure is applied to virtually create the effect of a mechanical differential lock. This means that the engine power is transferred to the road even more effectively. Traction can be improved further with the AMG rear axle locking differential available as an option from the AMG Performance Studio.

Newly developed AMG high-performance composite braking system

Along with the steering, the braking system is also a new development. The AMG high-performance composite braking system is characterised by high deceleration performance, a precise actuation point and excellent fade-resistance. Ventilated and perforated brake discs are fitted to both the front and rear axles. Because of the special stresses they face, the front discs feature composite technology that has been tried and tested in motor racing to help offset the temperature peaks more effectively. The front discs, measuring 390 x 36 mm, are decelerated using 6-piston aluminium fixed callipers, while the rear, measuring 360 x 26mm, use single-piston aluminium floating callipers. Grey-painted brake callipers with white AMG lettering are part of the standard equipment.

AMG ceramic composite high-performance brakes are available as an option and are recognisable thanks to the "AMG Carbon Ceramic" logo on the brake callipers. Thanks to the special materials and production technology used to manufacture the discs from carbon-fibre-reinforced ceramic in a vacuum at 1700 degrees Celsius, the ceramic discs are much harder. This not only increases the service life many times over compared with a grey cast iron disc, but also their resistance to extreme loads and heat. The result is extremely short stopping distances, an exact pressure point and much higher fade resistance even under extreme operating conditions. The larger ceramic discs – front: 402 x 39 millimetres; rear: 360 x 32 millimetres – feature a composite design all round and are connected with a floating radial mount to an aluminium bowl.

Compared with the conventional composite brake discs, the ceramic brake discs are around 40 percent lighter. The further reduction in unsprung masses not only boosts driving dynamics and agility but also improves steering response as well as ride comfort and contact characteristics. Six-piston fixed callipers are fitted on the front axle, and single-piston callipers are used on the rear.

Braking system data for the Mercedes-Benz SL 63 AMG at a glance:

Numerous functions of the high-performance braking system with ADAPTIVE BRAKE help to enhance comfort and safety. Take the practical HOLD function: if the SL 63 AMG has come to a stop, the driver simply needs to press the brake pedal a little bit firmer. The vehicle is now held by the brake – even if the driver takes their foot off the brake pedal. This prevents the vehicle from unintentionally rolling forward in stop-and-go traffic or inadvertently rolling back on an uphill slope. The HOLD function is automatically disengaged once the vehicle is driven forward. Another useful feature comes in the shape of the Hill-Start Assist. If the sensor technology detects that the driver wants to move off on an incline, the brake pressure is automatically maintained constant for a short period. This means the SL will not roll back and the driver has sufficient time to switch from the brake to the accelerator pedal without having to use the parking brake.

If the driver suddenly switches from the accelerator to the brake pedal prior to emergency braking, the braking system increases the pressure in the brake lines and applies the pads to the brake discs, so that they can grip instantly with full force when the brake pedal is pressed. The system supports the standard-fit Brake Assist by means of this 'priming'. Further standard features include the brake-drying function, which uses brief braking impulses to ensure the film of water on the brake discs is removed in the wet, thus considerably improving the responsiveness of the brakes.

Three light-alloy wheel variants to choose from

Three different AMG light-alloy wheels are available for the SL 63 AMG. As standard the Roadster comes with titanium grey-painted 5-twin spoke AMG light-alloy wheels with a high-sheen finish. The front axle is fitted with 255/35 R 19 tyres on 9.0 x 19 rims, while the rear has 285/30 R 19 tyres on 10 x 19 rims.

The weight-optimised AMG forged wheels from the AMG Performance Studio help to reduce the unsprung masses. Two different versions are available as an optional extra: multi-spoke AMG forged wheels in the format 9.0 x 19 (front) and 10 x 20 (rear) with 255/35 R 19 tyres on the front and 285/30 R 20 tyres on the rear – painted either in titanium grey and polished or painted in matt black with a high-sheen rim flange.

* Official photos and details courtesy of Mercedes-AMG GmbH *

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