Suspension: Agile and comfortable

Feb 2, 2018
Stuttgart/Amsterdam

There is a choice of suspension systems for the A-Class, depending on engine variant and driver preference. 16-inch wheels are standard equipment. DYNAMIC SELECT is standard equipment, and at the touch of a button also provides an individual driving experience in conjunction with active damping control (optional).

Like all its predecessors, the new A-Class has a McPherson front suspension. Wheel control is taken care of by one transverse control arm below the wheel centre, the McPherson strut and one tie rod. The transverse control arm in the new A-Class is a forged aluminium component. This reduces both weight and unsprung masses. The steering knuckles are made of cast aluminium.

The wheel-locating McPherson struts feature transverse force-optimised coil springs and twin-tube gas-pressure shock absorbers with auxiliary springs. The support bushing is a three-way design, with the forces applied by the damper, spring and auxiliary spring isolated from each other. Here too, attention was paid to low weight with a hollow piston rod, aluminium head bearing and a perforated spring plate. The tubular stabiliser is connected to the suspension struts by a newly developed, weight and friction optimised torsion bar linkage of hybrid polyamide construction.

When defining the axle geometry, particular attention was paid to keeping torque steer to a minimum and eliminating jolts as far as possible. The form and arrangement of the rubber bushings determines the great agility of the vehicle, also allowing a high level of ride comfort and driving safety.

Steering: also supports automated driving

The gearing of the electro-mechanical rack-and-pinion steering is located behind the wheel centre, and servo assistance is speed-sensitive as standard. The steering assistance function (in conjunction with the Driving Assistance package) is a new feature. The driver's steering movements to stabilise the vehicle are assisted by additional steering torque generated by the electric servo unit. 

These include:

  • countersteering in case of oversteer
  • steering corrections when braking on varying road surfaces (μ-split braking)
  • reducing the steering effects of front-wheel drive
  • compensation for crosswinds and road camber.

In combination with Active Distance Assist DISTRONIC, transverse control takes place to add active lane-keeping to the intelligent cruise control.

Rear axle: four control arms, high proportion of aluminium

The more powerful A-Class versions such as the A 250 and all 4MATIC models have a sophisticated four-link rear suspension. The three transverse arms and one trailing arm at each rear wheel are configured for maximum driving stability, comfort and longitudinal/lateral dynamics. The rear axle is mounted on a subframe isolated from the bodyshell by rubber bushings so that fewer vibrations are transferred from the suspension to the body.

The wheel carrier and spring control arm are made of aluminium – low unsprung masses allow a particularly sensitive "feel" for the road surface. All in all, the proportion of aluminium in the suspension components is one of the highest in any suspension system in this vehicle class. Newly developed shift rails made of polyamide connect the torsion bar stabiliser with the rear axle.

The entry-level A 200 and A 180 d models have a torsion beam rear suspension. Its U-section rotates in a targeted manner in one-sided compression and rebound, and acts as a stabiliser bar. The torsion-beam rear axle is secured to the body with two bearings and uses the same attachment points to the body-in-white as the multi-link axle's trailing arm.

Single-tube shock absorbers and separate coil springs are used for both the four-link and the torsion-beam rear axle. Here too, effective noise insulation of the coil spring between the body and rear axle is achieved with two elastomer insulators. The connection between the shock absorber and the body is via an aluminium bearing, which by way of its soft gimbal-type mount contributes to a reduction in friction in the damper and therefore to an improvement in response.

Three suspension variants: choice of setups

As standard the new A-Class is equipped with a comfort suspension with steel springs and DYNAMIC SELECT. The comfort suspension lowered by 15 millimetres has specially configured springs and dampers for more sporty characteristics.

The suspension with active damping control enables the driver to choose the preferred damping characteristics. A valve in each of the four shock absorbers is electronically actuated to control the oil flow. The damping characteristics are changed by regulation of the oil flow.

Several different sensors constantly monitor the suspension status, driving situation and driving style of the driver, and adjust the damping at each wheel. Information is also added by the engine, transmission, braking system, steering and driving assistance systems. The damping is specifically stiffened during acceleration, braking or steering manoeuvres to reduce pitching and body roll, and to improve wheel loads and tyre adhesion.

Brakes: ADAPTIVE BRAKE as standard

The new A-Class has a hydraulic dual-circuit braking system in X-configuration with the brake control function ADAPTIVE BRAKE as standard. The dimensions take vehicle-specific circumstances such as axle load distribution, weight and performance into account. The electric parking brake is standard equipment. The rear axle features a combined floating brake calliper with an electric parking brake function.

ADAPTIVE BRAKE puts technology from the top-of-the-line model Mercedes-Benz models into the A-Class. Thanks to electronic control, the hydraulic dual-circuit braking system allows assistance functions that improve safety and comfort. This includes priming of the braking system in critical situations: if the driver's foot moves abruptly from the accelerator to the brake pedal before an emergency stop, the braking system increases the pressure in the brake lines and brings the pads into contact with the brake discs so that maximum braking power is available as soon as the driver hits the brake pedal. This priming of the brakes allows the system to assist the standard Brake Assist.

ADAPTIVE BRAKE also brings safety benefits in wet conditions. The system briefly applies the brakes at regular intervals to wipe the film of water from the brake discs, ensuring that the brakes are able to perform at their peak. This automatic brake drying function is always activated when the windscreen wiper of the A-Class has been switched on for a certain time, and the finely metered braking impulses go unnoticed by the driver.

After braking to a standstill, briefly pressing the brake pedal a little further is all that is required to activate the HOLD function. The car is then held by the brakes, even if the driver's foot is taken off the brake pedal. In this way ADAPTIVE BRAKE prevents unintentional moving-off at traffic lights or in stop-and-go traffic, or rolling backwards on uphill gradients. The HOLD function is deactivated automatically when the car moves off.

The range of wheels and tyres begins at 16 inches. It comprises steel wheels in size 16 and 17 inches and light-alloy wheels in size 16 to 19 inches. The overall outer diameter of the wheels/tyres is 660 mm rather than the previous 645 mm.

Loading