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Suspension: Top-class technology for on and off the road

• New front and rear axle designs

• AIRMATIC air suspension for 291-millimetre ground clearance

• Adaptive Damping System for exemplary on-road performance

Whether taking bends at speed, on long motorway journeys or on difficult terrain, the suspension of the new M-Class is equal to any challenge. Mercedes engineers have newly developed the axles, steering, brakes and suspension, and adapted them to match the varied operating requirements of the Off-Roader. The result is a technical masterpiece which meets the highest demands in terms of both handling dynamics and ride comfort. Individual customer wishes can now also be met with respect to suspension technology: available options include an AIRMATIC package with the Adaptive Damping System (ADS) and the Off-Road Pro engineering package with differential locks, low-range ratios, an underride guard and AIRMATIC with extended functions for even greater ground clearance.

The front wheels are located by a newly developed double-wishbone suspension whose upper wishbone is located in a high position. In conjunction with the robust subframe, engine, transmission, steering and axle, this suspension principle has enabled Mercedes engineers to achieve an ideal compromise between a high load-bearing capacity, good ride comfort and exemplary handling characteristics. The upper wishbone is of forged aluminium, while the lower wishbone and steering knuckle are of nodular cast iron. Four rubber bearings isolate the subframe from the vehicle body and make a major contribution to the vibration comfort of the new M-Class.

This front suspension with its high control arms is equipped with spring struts whose longer spring travel and more effective rubber bearings provide better ride comfort than the preceding series. The spring struts contain cylindrical coil springs, single-tube gas-pressure shock absorbers and large head bearings. The torsion bar stabiliser is attached to the spring strut by a linkage.

Speed-sensitive power steering as standard

The steering gear of the new M-Class is positioned in front of the wheel centre, and therefore where it can support the slight but easily controlled understeer of the Off-Roader on bends. The servo-assisted rack-and-pinion steering has a variable ratio which operates a little more directly in the central position than in the outer positions. Additional comfort is provided by the speed-sensitive power steering, which continuously reduces the steering effort below 100 km/h as a function of vehicle speed. This is made possible by an electronically controlled valve: the lower the speed, the higher the servo effect. Accordingly only half the steering effort is required when parking the vehicle than when driving on the motorway, where the speed-sensitive power steering provides good road contact. This comfort feature is standard equipment in the new Mercedes Off-Roader.

Mercedes-Benz has developed a four-spoke steering wheel with a diameter of 385 millimetres for the M-Class whose die-cast magnesium structure is designed to deform specifically during a frontal collision, thereby reducing the risk of injury to the driver. The steering wheel is an important part of the operating and display concept with its conveniently placed, illuminated keys, as it allows various functions such as the radio, car telephone or the central display in the instrument cluster to be operated by slight thumb pressure.

The newly developed steering column, which is able to collapse telescopically by up to 100 millimetres during a frontal collision, can be individually adjusted for height and reach. Electric adjustment is also available as an option.

Newly developed four-link technology at the rear axle

Like the front axle, the rear axle is mounted on a subframe which is effectively isolated from the bodyshell by two rubber bearings and two hydro-mounts. Mercedes engineers have developed a four-link suspension design which basically consists of the following elements:

• Lower wishbone: This axle component is made from nodular cast iron.

• Upper steering arm: This is an assembly of sheet steel camber arms and forged steel rods.

• Track rods: These are located behind the wheel centre and are of welded tubular construction.

The rear axle coil springs and single-tube shock absorbers are positioned in line. A torsion bar stabiliser is also used.

AIRMATIC air suspension in on-road and off-road configurations

The AIRMATIC air suspension system (optional) developed by Mercedes-Benz proves its versatility in the new M-Class. It not only makes a significant improvement to ride comfort, but also offers additional functions for off-road driving.

Mercedes customers are offered a choice: the AIRMATIC package provides an air suspension configured for on-road operation which automatically lowers the suspension by 15 millimetres at higher speeds. For off-road driving this system enables the ground clearance to be increased by 80 millimetres at the touch of a button. The second AIRMATIC variant, which is part of the Off-Road Pro engineering package, enables the vehicle level to be raised in three stages by operating a button: by 30, 80 and 110 millimetres. This gives the new M-Class its maximum ground clearance of 291 millimetres.

It is possible to raise or lower the suspension both when idling or on the move. If the M-Class is moving, the system operates on a speed-dependent basis and automatically lowers the suspension by 15 millimetres at both axles when 140 km/h is reached, in order to reduce the wind resistance and improve handling stability. When the speed falls below 40 km/h the suspension is raised to its normal level again. Other features of the air suspension system include an automatic all-round level control function, which ensures that the suspension travel remains constant even when the vehicle is heavily laden.

The suspension level settings at a glance:

*automatic lowering

Adaptive shock absorber control according to the driving situation

In both variants AIRMATIC works as standard together with the Adaptive Damping System (ADS), which controls the shock absorber response in line with requirements while taking the road surface, driving style and load into consideration. Selectable solenoid valves in the shock absorbers enable the rebound and compression damping to be modified according to the situation, which considerably reduces body movements. The so-called skyhook algorithm controls the damping forces at each wheel in such a way that the wheel-induced forces acting on the vehicle body are reduced. Thanks to this precise control for each individual wheel, the two front wheels can e.g. be damped more heavily than the rear wheels to reduce the tendency of the body to dive when braking. Depending on the control command, the valves are able to select one of four characteristic curves within an extremely short response time of less than 0.05 seconds:

• Stage 1: Comfortable suspension action with small body movements and low acceleration values owing to soft compression and rebound settings.

• Stage 2: Skyhook mode – soft rebound setting and a hard compression setting.

• Stage 3: Skyhook mode – soft compression setting and hard rebound setting.

• Stage 4: Hard rebound and compression setting to reduce wheel load fluctuations when cornering at speed.

When body movements are small the new M-Class operates in ADS stage 1. If body acceleration values exceed a certain level, the system changes over to the skyhook algorithm and uses its rapid-response solenoid valves to continuously switch between the second and third damping stage to compensate the rolling and pitching movements of the vehicle body. The current driving situation is identified by means of a steering angle sensor, three body-mounted acceleration sensors, the speedometer signal giving the road speed, data from the Electronic Stability Program (ESP®) and the signal from the brake pedal switch. On the basis of this information the electronic control unit calculates the most efficient damping forces and selects the relevant characteristic curves for the shock absorbers.

In addition the driver is able to influence the changeover thresholds between the four ADS stages, as well as the spring rate, by pressing a button in the centre console. There is a choice of three modes: "Auto", "Sport" and "Comfort".

The variable ADS gas-pressure shock absorbers and air spring are integrated into a spring strut at the front axle of the new M-Class. At the rear axle the ADS shock absorber is located behind the air spring. Torsion bar stabilisers are also used at both the front and rear.

Larger front and rear brake discs

The new M-Class features generously dimensioned, internally ventilated front brake discs. In the six-cylinder models these have a diameter of 330 millimetres -27 millimetres more than before. The top-of-the-line ML 500 is equipped with even larger brake discs (350 millimetres). At the rear axle Mercedes-Benz uses solid disc brakes with a diameter of 330 millimetres - 45 millimetres more than in the previous M-Class. The data for the braking system at a glance:

Sports package with 19-inch light-alloy wheels

Wide-base tyres and 17 or 18-inch light-alloy wheels underline the sporty, dynamic appearance of the new M-Class. The six-cylinder models are fitted with 17-inch light-alloy wheels in a seven-spoke design and size 235/65 R 17 wide-base tyres as standard. The ML 500 has 18-inch light-alloy wheels in the five-spoke "impeller" design and size 255/55 R 18 tyres. A different 18-inch wheel in a five-twin-spoke design with 255/55 R 18 tyres is optionally available for all the model variants. Here is a brief summary:

The wheels Mercedes-Benz offers in conjunction with the sports package are even larger and more attractive: these 19-inch light-alloy wheels in a five-spoke design are also optionally available in a chrome-plated version which creates an additional visual highlight.

ESP® with tyre pressure warning function

ABS, ASR, ESP®, Brake Assist – these well-proven dynamic safety systems developed by Mercedes-Benz are standard equipment in the new M-Class.

The Electronic Stability Program not only keeps the Off-Roader safely on course, but also monitors the tyre pressures in its latest version: the system continuously compares the wheel rotation speeds, which mainly depend on the vehicle speed, vehicle load and tyre pressures. It is therefore able to detect any significant deviations. In addition the control unit automatically monitors other dynamic parameters such as the lateral acceleration, yaw rate and wheel torque in order to diagnose any pressure loss in a tyre reliably, though this system does not measure the actual air pressure in each tyre. If a loss of pressure is detected in a tyre, a warning appears in the cockpit’s central display: "Tyre pressure, check tyres." This warning function for tyre pressure loss based on ESP® technology is standard equipment in the new M-Class.

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