The new Mercedes-Benz SLS AMG - PART V


Laguna Seca, USA, Nov 02, 2009

Chassis and braking system: High-tech from motor racing for perfect racetrack performance

- Aluminium suspension with double-wishbone axles
- Performance suspension with a stiffer setup on request
- "Flow Forming" AMG light-alloy wheels of 19 and 20-inch size
- 3-stage ESP® and mechanical multi-plate differential lock
- New ceramic composite high-performance braking system available as an option

The motor sports derived technology to be found everywhere in the powertrain of the Mercedes-Benz SLS AMG is also evident in the suspension and braking system. The aluminium suspension with double-wishbone axles is designed for uncompromising lightweight construction and outstanding handling dynamics. On request the AMG high-performance braking system is also available in a newly developed, highly stress-resistant ceramic version, with composite brake discs all-round.

The commitment of Mercedes-Benz and AMGto building a highly desirable super sports car that combines consummate racetrack performance with hallmark Mercedes long-distance comfort has given rise to an ingenious suspension layout. All four wheels are located on double wishbones with a track rod, a technology that has proven itself in motor racing right through to Formula 1. With a double-wishbone axle, the wheel location and suspension functions remain separate; the spring/damper struts are supported on the lower wishbone. The double-wishbone concept with its high camber and track rigidity positively locates the wheel with minimal elastic movements, providing the driver with an optimum sense of road contact when driving at the limits.

The suspension setup of the SLS AMG ensures optimum, low body roll and a stiff basic configuration with good suspension comfort. A Performance suspension is also available on request: compared to the standard suspension, the spring rate and damping are respectively around 10 percent and 30 percent stiffer. The Performance suspension is conducive to even more agility and lateral dynamics, as well as a further reduction in body roll when driving at high speeds – for example on the racetrack.

Long wheelbase and wide track

The long wheelbase of 2680 millimetres not only results in outstanding straight-line stability but also low wheel load shifts, significantly reducing the vehicle's tendency to dive and squat when braking and accelerating. The broad track width – front 1682, rear 1653 millimetres – ensures lower shifts in the wheel loads from the inner to the outer wheel when cornering, enabling the tyres to retain more grip. The large caster angle of 11.6 degrees significantly increases negative wheel camber on the outer wheel when cornering, and also improves tyre grip – this also ensures outstanding stability when braking heavily while cornering.

Weight-optimised "Flow Forming" AMG light-alloy wheels

The weight-optimised axle design is complemented with AMG light-alloy wheels produced by the new "flow forming" process. During this production process, hot forming in the area of the rim base makes for a denser material structure, thereby improving long-term durability. This also means that lower wall thicknesses can be used. The weight saving of around 1.1 kilograms per wheel compared to conventional light-alloy wheels reduces the unsprung masses, further improving the handling dynamics and suspension comfort.

The AMG light-alloy wheels in size 9.5 x 19 inches at the front and 11.0 x 20 inches at the rear are shod with 265/35 R 19 size tyres at the front and 295/30 R 20 at the rear. Three variants are available: AMGlight-alloy wheels in a 7-spoke design or a 5-twin-spoke design, or alternatively low-weight forged wheels in a 10-spoke design. With an approx. 14-percent lower weight than the "Flow Forming" wheels, these reduce the unsprung masses even further. The weight saving per wheel is 1.8 kilograms. Tyres developed exclusively for the SLS AMG ensure top performance and excellent grip.

A tyre pressure control system which continuously monitors the pressure in all four tyres is standard equipment, with the data for each wheel shown in the display. During a journey, four wheel sensors on the insides of the light-alloy wheels send out continuous radio signals with information about the air pressure, tyre temperature and direction of rotation. A control unit evaluates the data and informs the driver in the event of a deviation from the nominal values. In this case the display shows the message "Check tyres!", or in case of a sudden pressure loss "Attention. Tyredefect!". A yellow warning lamp also lights up in the instrument cluster.

Power-assisted rack-and-pinion steering for direct feedback

With a constant mechanical steering ratio of 13.6:1, the rack-and-pinion steering of the SLS AMGprovides direct feedback and meets the high expectations for a super sports car. The servo assistance is speed-sensitive, improving the feedback to the driver as the speed increases – an indispensable factor when driving straight ahead at high speed. Perfect linear transfer of the steering angles is made possible by the constant velocity joint integrated into the steering system. The chosen geometry also provides plenty of scope for the performance-enhancing headers in the sports exhaust system.

Installing the steering gear on the subframe in front of the engine allows a particularly low engine position. The subframe is of high-strength steel, and is rigidly bolted to the side members. It not only optimises steering precision, but is also a key component in the front-end crash structure.

AMG high-performance braking system with composite technology

High deceleration performance, precise pedal feedback, perfect fade-resistance and superior safety reserves are the key attributes of the AMGhigh-performance braking system. Ventilated, grooved and perforated brake discs all-round in size 390 x 36 millimetres at the front and 360 x 26 millimetres at the rear ensure excellent deceleration performance. Brake discs in race-tested composite technology are installed at the front axle, with the grey cast iron discs radially and axially floating, and fixed to an aluminium bowl via stainless steel connections. This sophisticated technology ensures highly efficient heat conduction, and therefore outstanding fade-resistance even with a highly dynamic style of driving.

The use of aluminium also saves weight, and in the case of the brakes this has particular advantages in terms of agility and suspension responsiveness because of the considerable reduction in unsprung masses. Six-piston fixed callipers at the front and four-piston fixed callipers at the rear allow a generous brake lining surface area of 2 x 120 sq. cm and 2 x 58 sq. cm. The AMG high-performance braking system achieves a braking output of 816 kW/1109 hp during emergency braking from 250 km/h to standstill.

High-performance ceramic composite braking system as an option

A high-performance ceramic composite braking system is available as an option. This is instantly recognisable by the specially painted brake callipers with "AMGCarbon Ceramic" lettering. Thanks to the special materials and production technology used to manufacture the discs from carbon-fibre reinforced ceramics 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 the 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 – are of composite construction and are connected to an aluminium bowl by a floating radial mounting. At 823 kW/ 1120 hp during emergency braking from 250 km/h, their braking performance is even higher than that of the AMG composite braking system.

The ceramic brake discs are 40 percent lighter in weight than the conventional, gray cast iron brake discs. The further reduction in unsprung masses not only improves handling dynamics and agility, but also ride comfort and tyre grip. The lower rotating masses at the front axle also ensure a more direct steering response – which is particularly noticeable when taking motorway bends at high speed. The ceramic discs are also corrosion-proof, and therefore unaffected by deicing salt and brine. Six-piston fixed callipers with a brake lining area of 2 x 154 sq. cm. are installed at the front, with four-piston fixed callipers and a lining area of 2 x 73 sq. cm. at the rear.

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

Both AMG high-performance braking systems feature precisely configured cooling ducts: the airflow entering the apertures in the front apron is conducted directly to the front brake callipers, helping to lower peak temperatures in the brake fluid – for example when driving at very high speeds on a racetrack.

Efficient anti-locking system and 3-stage ESP®

The specification of the braking system includes an anti-locking system with demand-controlled brake distribution. When braking on bends, a yawing moment is produced which counteracts and stabilises the vehicle's tendency to turn on its own axis. The braking system uses the data supplied by the ESP® sensors in order to identify such situations reliably.

The Electronic Stability Program is designed as a sophisticated 3-stage ESP® with a sports function – a speciality exclusive to AMG. Perfectly configured to match the outstanding driving dynamics of the SLS, 3-stage ESP® has three different settings. Using the ESP® key in the AMG DRIVE UNIT, the driver is able to choose between "ESP ON", "ESP SPORT" and "ESP OFF" – the currently active mode is shown in the display of the AMG instrument cluster. In "ESP ON" mode, there is braking intervention at one or more wheels and a reduction in engine torque if the car starts to become unstable.

Briefly pressing the ESP® key activates "ESP SPORT". 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 terms of driving
dynamics, the engine torque is also no longer reduced in this case. "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. Acceleration skid is controlled in all three ESP® modes. As soon as a drive wheel begins to spin, traction is significantly improved by specific braking
intervention and interaction with the standard, mechanical multi-plate differential lock. This enable the engine power to be transferred to the road even more efficiently when driving in particularly dynamic style.

Hill-holder function improves comfort and safety

Numerous functions of the high-performance braking system also improve comfort and safety, for example the hill-holder function. When the sensor system detects that the driver wishes to move off on a gradient, the hill holder function is activated automatically and maintains a constant brake pressure for a short time to prevent the car from rolling backwards. This gives the driver enough time to move his foot from the brake to the accelerator without first engaging the parking brake.

If the driver suddenly takes his foot off the accelerator 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 Brake Assist by means of this 'priming'. Further standard features include the brake-drying function, which uses brief braking impulses to ensure that the film of water on the brake discs is removed in the wet, thus considerably improving the responsiveness of the brakes.

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