BMW M5 – Body and chassis: Perfect for fast laps – and long hauls







Published by Gerald Ferreira Date: February 1, 2012
Categories: BMW, BMW M5

  • Lightweight chassis tuned on the Nürburgring.
  • Active M Differential delivers optimised traction; adjustable configuration for Dynamic Damper Control and M Servotronic.
  • Body with outstanding torsional rigidity and stiff axle mounts using special struts and panels.

The new BMW M5 is a high-performance sports car whose exceptional dynamic potential is geared squarely to the demands of track use, yet which also sets a new benchmark in everyday driving with its supreme touring comfort. Chassis technology geared to the demands of racing, with stronger yet also more lightweight axle links and wheel carriers, enables precise handling even in extremely dynamic driving situations.

The torsionally stiff body – with axle mounts using high-strength panels – and the high-performance braking system with hallmark M compound construction are designed to withstand the extreme loads of committed, sporty driving. The precise interplay of powertrain, chassis and body has been fine-tuned down to the last detail during extensive testing at the Nürburgring’s Nordschleife circuit, and ensures peerless longitudinal and lateral acceleration, handling and braking.

Among the chassis systems fitted as standard on the new BMW M5 are Dynamic Damper Control, M-specific Servotronic steering and DSC (Dynamic Stability Control) with M Dynamic Mode. Like the engine responses and the transmission’s shift program, the characteristics of these systems can be adjusted according to need. This allows the driver to further sharpen the sporting character of their new BMW M5 or give it a more comfort-oriented set-up – ideal for relaxed long-distance journeys in the spacious and luxurious surroundings of a top-class premium sedan.

Innovation for unbeatable traction in dynamic driving situations: the Active M Differential.

BMW M cars are equipped with a specially developed differential for the rear axle to allow the driver to enjoy the benefits of rear-wheel drive to the full – in the form of the sharpest possible driving dynamics. A variable locking function splits engine power between the right and left rear wheel to generate maximum traction. Another innovation in this area that is fitted in the new BMW M5 ensures even more precise distribution of drive according to the situation at hand; the Active M Differential optimises stability with the help of an electronically controlled multi-plate limited-slip differential, which intervenes at an early stage to prevent wheel spin.

BMW-M5 2012

The rear axle’s multi-plate limited-slip differential works with extremely high precision and speed. Its control unit is connected with the DSC (Dynamic Stability Control) system via FlexRay high-speed data transfer technology and constantly cross-checks the data collected by its sensors with the feedback from DSC. It then uses this information to calculate the locking force required to deliver optimum traction and stability. The data recorded by DSC sensors is also passed on if the stability control system is switched off. The locking force within the differential can be set between 0 and 100 per cent. The Anti-lock Braking System retains full functionality in all situations.

In addition to its own data and that provided by DSC, the Active M Differential’s control unit also takes into account the position of the accelerator pedal, the rotational speed of the wheels and the car’s yaw rate. Every driving situation is therefore precisely analysed and an impending loss of traction on one side of the car identified at an early stage. The degree of lock is adjusted as required within a fraction of a second, enabling wheel spin to be prevented on slippery surfaces, in instances where the right and left rear wheel have widely differing friction coefficients, in tight bends and when changing direction extremely dynamically. Optimising traction in this way also provides unbeatable driving stability in challenging conditions and allows impressively dynamic acceleration out of corners. Plus, the Active M Differential also counteracts – to great effect – a loss of traction during double lane changes at high speed and a tendency to understeer under sudden load alterations during dynamic cornering.

M-specific chassis: lightweight, torsionally stiff and extremely durable.

Like its integral rear axle, whose subframes are bolted rigidly to the body and attached to the longitudinal members by additional braces, the double-wishbone front axle of the new BMW M5 boasts special kinematics and newly developed components made from forged aluminium. The use of this lightweight metal for the control arms and support elements gives the components a reinforced geometry and reduces weight. Like its track width and wheel camber, the lowered suspension of the new BMW M5 is also geared to its high-performance character.

Using large panels to fix the chassis to the front and rear axles optimises torsional rigidity and ensures that the dynamic forces are channelled evenly through the body. For example, the forces exerted on the anti-roll bars on one side of the car when clipping a kerb on the track are transferred evenly over the entire front section of the car.

Fitted as standard: electronically controlled dampers with three settings.

The new BMW M5 is equipped as standard with electronically controlled dampers. Dynamic Damper Control uses electrohydraulic damping force adjustment to provide a set-up suited to the driving situation or the wishes of the driver. The bespoke dampers feature electronically controlled valves integrated into the pistons that react to the vertical movements of the wheels in fractions of a second. The progressive set-up of the rear suspension ensures flexible responses, while also allowing high loads. Indeed, the type of bumps and ruts encountered every day on the road are smoothed out by small adjustments, while under heavier loads and greater suspension travel the spring rate increases disproportionately.

At the touch of a button, the driver can choose from three settings to determine the vehicle’s damping characteristics. In “Comfort” mode the dampers respond adaptively to the condition of the road surface and the driver’s style. “Sport” mode activates a noticeably stiffer damper set-up, while “Sport Plus” allows further stiffening of the suspension to achieve maximum longitudinal and lateral acceleration in ultra-dynamic driving situations on level race tracks.

M-specific Servotronic steering, DSC stability control including M Dynamic Mode.

The hydraulic rack-and-pinion steering with variable ratio is another M-specific feature, combining precise directional stability with a need for less steering effort when manoeuvring. Sharply turned-in wheels prompt a lower steering ratio, reducing the number of steering movements required of the driver.

The speed-sensitive Servotronic power assistance in bespoke M configuration has three settings, which can be selected at the touch of a button. “Comfort” mode reduces the amount of steering effort required when parking and manoeuvring, but ensures hallmark BMW precision when steering at higher speeds. “Sport” mode delivers more direct signals through the steering wheel at all speeds. And “Sport Plus” takes steering feedback to an even higher level and demands greater energy from the driver at the wheel.

In addition to applying brake impulses and reducing engine output to stabilise the car, the DSC system in the new BMW M5 also employs the services of the Anti-lock Braking System (ABS), Cornering Brake Control (CBC) and Dynamic Brake Control (DBC), as well as a Brake Assistant, Brake Drying function and Start-Off Assistant. M Dynamic Mode (MDM) can be activated to override the basic setting by pressing the DSC button on the centre console. This mode generates the familiar M self-steering response by raising the intervention thresholds of DSC. “DSC Off” mode can also be activated at the touch of a button.

Taken to another new level: the compound high-performance braking system.

The high-performance braking system of the new BMW M5 guarantees outstanding stopping power. The further development of the remarkable compound construction has resulted in further optimised braking performance – resisting fade even under heavy loads – and an enviable degree of feel. To this end, the size of the grey-cast iron friction rings has been increased and the weight of the aluminium brake-disc bowls further reduced. The inner-vented and perforated brake discs have a diameter of 400 millimetres at the front and 396 mm at the rear. The six-piston fixed-calliper brakes are radially bolted to the pivot bearing. The single-piston floating-calliper brakes at the rear wheels are also used for the electric parking brake.

The M-specific light-alloy wheels for the new BMW M5 come in 19-inch format as standard and are fitted with 265/40 R19 tyres at the front and 295/35 R19 items at the rear. 20-inch forged M light-alloy wheels with 265/35 R20 and 295/30 R19 tyres at the front and rear respectively can be ordered as an option. The wheels’ low spoke count means that the brake callipers – painted dark blue metallic and complete with the M logo – are clearly visible.

Extensive safety equipment, extremely impressive power-to-weight ratio.

Hallmark M handling and occupant protection both benefit from the extraordinary strength of the BMW M5 body structure. Incredibly durable load-bearing structures and large, precisely defined deformation zones keep the forces released in a collision away from the extremely rigid passenger compartment. The safety equipment fitted as standard in the new BMW M5 includes front and side airbags, side curtain head airbags for both rows of seats, three-point inertia reel seat belts on all seats, front belt force limiters and belt tensioners, and ISOFIX child seat attachments in the rear.

An intelligent mix of materials containing a high proportion of high-tensile and ultra-high-tensile steels, as well as aluminium, help to minimise the car’s weight. Like the bonnet and front side sections, the doors of the new

BMW M5 are also made from aluminium. With a power-to-weight ratio of 3.3 kg, the high-performance Sedan represents a substantial step forwards from its predecessor in this area as well.

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