BMW M5 Forum and M6 Forums banner

1 - 1 of 1 Posts

49,477 Posts
Discussion Starter #1
One of the guiding principles when designing an M vehicle is:
“The suspension must always be faster than the engine.” Due to the new M5 engine’s high-revving concept, this self-commitment means that suspension designers at BMW M GmbH are faced with an extremely fastidious task.

Basis of the M5 suspension is the all-aluminium suspension of the
basic 5 Series, the kinematics of which were adapted to the more powerful M5. The extremely stiff body construction used for the 5 Series and the
large proportion of light aluminium axle components and ancillary parts are ideal preconditions for achieving optimum driving pleasure. These features
are supplemented by a well-balanced, almost 50:50 weight distribution
on the front and rear axles and, of course, the typical BMW rear-wheel drive that keeps the steering entirely free from drive forces.

The basic geometry of the 5 Series suspension was maintained. The track is 1,580 mm at the front and 1,566 mm at the rear, the wheel base measuring 2,889 mm. Having a substantially negative camber, the wheel guidance does full justice to the higher demands placed on driving dynamics and increased loads.

In the interest of sportiness: suspension assisting systems.

The M5’s Electronic Damper Control (EDC) allows the driver to adjust the suspension’s characteristics from sporty to comfortable by utilising a choice of three different modes – comfort, normal and sport. The driver operates
EDC via the MDrive button on the steering wheel or by means of a push button adjacent to the SMG selector lever.

The M5’s suspension also features optimised DSC Driving Stability Control. Weight-optimised rack-and-pinion steering with two Servotronic control maps was especially adapted for use in the M5.

Intelligent lightweight construction: low masses – high degree
of stiffness.

Like on the basic model, the double-joint spring-strut front axle is made entirely of aluminium, with the exception of a few components subject to heavy loads such as the track rod, wheel bearings or pivot pins. The front axle subframe accommodates the steering transmission, anti-roll bar, transverse control arm and tension rods. It is U-shaped and reinforced by a special thrust plate. As opposed to the basic model, this thrust plate features two so-called

NACA air intakes well-known from motor sport or aviation. Thanks to these intakes, cooling air is directed, inter alia, to the gearbox without adversely affecting the aerodynamics of the underbody. The aluminium thrust plate facilitates maximum lateral stiffness of the front axle subframe. This in turn results in particularly precise response behaviour. The bearings on the
front axle subframe ensure accurate wheel guidance due to employment of separate bearings for suspension and dampers.

Servotronic with two control maps.

Servotronic controls the power assisted steering independently via
control maps, depending on the road speed and engine speed. This solves the fundamental problem of obtaining a balance between a high level of assistance for best possible parking comfort and the low level of assistance required for dynamic driving at high speeds. The driver is then in less danger
of “tearing” at the steering wheel while suddenly swerving to avoid an obstacle.
The M5 features two different Servotronic mappings, both corresponding
with the currently prevailing EDC mode, i.e. either a very sporty or a more comfortable mode. In the sporty mode steering is very direct and the driver receives an immediate, precise response during the high lateral acceleration that occurs when taking fast bends. The comfort mode gives preference
to motoring comfort. Both mappings provide the driver with even steering behaviour and optimum response.

Rear axle: optimised for the M5.

The rear axle, which is made almost entirely of aluminium, is essentially based on the integral axle featured on the 7 and 5 Series. This design, which is outstanding in terms of road holding and comfort, was adapted to the M5’s distinctively higher standards through the utilisation of special elastokinematics and reinforcements in all relevant areas such as supports, links and joints. For example, rubber link joints have been replaced by rigid elements. This guarantees an even more accurate guidance and centring of the wheels. The M5’s final drive has been entirely reconceived with a view to keeping masses low and conveying power efficiently. By means of cooling fins on the aluminium differential cover, the engineers managed to reduce peak temperatures produced in the rear axle by 15 degrees Celsius compared to a conventional design. This results in substantially reduced thermal load on components. The final drive is connected to the seven-speed SMG gearbox via a two-piece cardan shaft featuring a Hardy disc at the front, a constant-velocity joint at the rear and a centre bearing. The output shafts feature a lightweight, torsionally stiff tubular design in order to keep movable masses as low as possible.

Variable M differential lock.

Like the M3, the sportiest member of the family until now, the M5 features
a rear axle differential with variable, torque-sensing differential lock developed by the M GmbH. This M differential lock provides the vehicle with both
a high level of driving stability and optimum traction, especially when driving out of bends.

M differential lock for more driving fun and enhanced safety.

A differential lock produces locking power when required. This principle takes effect when one of the two driven wheels is about to spin – on a slippery surface for instance. Furthermore, the differential lock is well-appreciated by sports-minded drivers, as it helps enhance the positive qualities of rear-wheel drive when the vehicle is being driven in a sporty manner and on roads with an average to high coefficients of friction.

Providing excellent winter driving characteristics.

In the case of ‘standard’ torque-sensing differential locks, the overall transferable drive forces correspond to the forces the wheel with the lower coefficient of friction can convey. However, if the frictional coefficient
is very low, for example on snow, gravel or ice, the advantages in traction obtained by this conventional differential lock concept are limited.
The variable M differential lock is able to provide a substantial advantage in traction even in extremely demanding driving situations – for instance
when the driven wheels are subject to greatly varying coefficients of friction. Therefore, combined with the finely tuned DSC system and the well-balanced distribution of axle load, the variable M differential lock helps the M5 in delivering excellent winter driving characteristics.

Forward progress maintained in any situation.

A further advantage of the variable M differential lock is the fact that an increasing locking power is immediately generated as the differential speed between the driven wheels increases. This prevents the wheel – e.g. the
wheel nearest to the inside of a bend while driving over a pass at high speeds for instance – from losing drive forces. Forward progress is maintained
at all times.

100 percent locking power.

The variable M differential lock functions according to the following principle: the differential speed that builds up between the driven wheels when a driven wheel threatens to lose traction or runs on a very slippery surface immediately generates pressure in an integrated shear pump. This pressure is transferred to a multiple-disc clutch by means of a piston, by which drive forces are conveyed to the wheel with the better grip, according to the difference in wheel rotational speed. In extreme cases, the entire drive forces may be transmitted to the wheel with a better frictional coefficient. If the difference in rotational speed between the two wheels decreases, the pump pressure also inevitably decreases, with locking action diminishing accordingly. This self-regulating pump system is maintenance-free and filled with high viscosity silicone oil.
The driver benefits from the fact that he can drive off far better in his M5 on surfaces on which the drive wheels are provided with greatly varying frictional coefficients, as he then has more traction at his disposal. Moreover, the variable M differential lock also noticeably enhances handling and driving stability – an additional advantage in terms of safety and driving pleasure.

Featured only in the M5: DSC with a choice of two driving
dynamics programs.

A new generation of Dynamic Stability Control (DSC) was developed exclusively for the M5: the DSC system can be deactivated via a switch on the centre console. Its driving dynamics programs are pre-selected using the so-called MDrive menu and can be called up by pressing the MDrive button on the steering wheel. Whilst the first stage of DSC essentially corresponds to that of the 5 Series, the second stage – the M Dynamic Mode – will appeal to the particularly sport-orientated driver.

M Dynamic Mode – awesome driving dynamics.

M Dynamic Mode (MDM) is a unique feature in the achievement of driving dynamics and an awesome experience for the driver with racing ambitions. Until now a similar feature was found only in the M3 CSL high-end racing machine and was known as M Track Mode. This subfunction of Dynamic Stability Control adapted for deployment in motor sport allows the M5 driver to push the car to the absolute limit of longitudinal and lateral acceleration
at the touch of a button located on the steering wheel. Those who choose to use this option can challenge the laws of physics. In this mode DSC is
not activated until the absolute limits have been reached, thereby permitting a sideslip angle the driver can just about cope with by means of moderate countersteering. The M Dynamic Mode should, understandably, be reserved for use on the cordoned-off racing track. The driver is informed of the M Dynamic function by a warning lamp on the instrument panel. Finally, the driver is able to completely deactivate the DSC function. He is also informed of this by means of a warning lamp.

A significant increase in safety with DSC.

DSC is a safety feature which cuts in when reaching the boundaries of physics. Through effective intervention in the engine control system and brakes on each individual wheel, the system enhances motoring safety,
for example on slippery surfaces, when swerving abruptly or when stability
is threatened in bends.

Power button activates engine characteristics “on demand”.

Frequently, the driver does not require the M5’s full power output and maximum agility, for example in town traffic. For this reason, when the car is started, the markedly comfortable P400 power mode with 400 bhp is automatically activated. However, simply by pressing the Power button situated on the selector lever cover, the driver has at his disposal the full power of ten cylinders. This converts the accelerator pedal kinematics to a spontaneous characteristic, the P500 mode facilitating sporty driving pleasure and the P500 sports mode providing the driver with an uncompromising motor sport experience.

EDC: from sportingly firm to comfortable.

The M5’s Electronic Damper Control (EDC) allows the driver to adjust the suspension’s characteristics from sportingly firm to comfortable by making a choice between three modes – comfort, normal and sport. The driver
operates EDC via the MDrive button on the steering wheel or by pressing the push button located adjacent to the SMG selector lever.
EDC is a continuous and infinitely variable electronic damping control with
a wide range of adjustments. In “normal” mode the damping force is automatically adjusted as required. This system is synonymous with optimum motoring comfort and safety. Additionally, the driver can pre-select the damping characteristic using the “comfort” or “sport” mode. In sport mode, the suspension reacts to road surface conditions by employing higher damping forces, thereby reducing the lifting effect, which noticeably improve the limpet-like grip. In the comfort mode EDC produces lower damping forces in favour of greater motoring comfort.

EDC increases motoring safety.

In bends and when braking and accelerating, motoring safety is enhanced
in all modes due to a higher level of damping force. This also facilitates an improvement in the vehicle’s body roll and swaying characteristics.
The vehicle’s consistently excellent vibrational properties, irrespective of
load and throughout its entire life cycle, are a further advantage.

High-performance brakes also employed in motor racing.

To complement its immense power output, the M5 features an amply dimensioned high-performance braking system with perforated, extremely weight-optimised compound brake discs derived from motor sport. As in motor racing, stringent testing has also determined the optimum arrangement and shape of the perforation for excellent braking properties in both wet and dry conditions. The wheels sport 374 x 36 mm brake discs at the front and 370 x 24 mm brake discs at the rear.

The M5 comes to an “immediate” halt whenever required.

The weight and stiffness-optimised aluminium twin-piston sliding callipers (analogous to the BMW 7 Series) also substantially reduce unsprung weight, thereby contributing towards maximising agility, safety and motoring comfort. As a result, the M5 achieves stopping distances normally only accomplished by sports cars of the highest calibre. When the brakes are applied at 62 mph, the car comes to a halt after just 36 metres, from 124 mph the braking distance is less than140 metres.

Diagnostic system for brake pad wear.

The M5 features a diagnostic system for brake pad wear. A wear sensor monitors brake pad wear at specific measuring points and transmits these values to the DSC control unit. The system then calculates, depending
on the driving behaviour, the current condition of the brake pads and – having this information at hand – forecasts the residual mileage before the brake pads have to be changed. This information is utilised by the Condition Based Servicing (CBS) to calculate adequate proposals for service intervals in order to minimise maintenance work.

The wheels – visually and technically a feast for the eye.

The car has large-diameter brake discs, so the wheels had to be given larger dimensions accordingly. However, the 8½ and 9½ inch wide and 18 inch high cast-aluminium rims supplied as standard also visually emphasize the M5’s dynamic appearance, as they complement the well-balanced body proportions.

Special tyres designed exclusively for the M5.

The M5’s tyres are not supplied off the peg. The car boasts 255/40 ZR 19 tyres at the front and even 285/35 ZR 19 tyres at the rear. They were developed exclusively for the M5 and have undergone stringent testing.
The rubber compound and the dimensions were designed for precise transfer of lateral and longitudinal forces in both dry and wet road conditions and offer a relatively high degree of motoring comfort. The tyres also possess the respective feedback properties required to provide the driver with an optimum motoring experience reaching the threshold of what is physically possible.

Tyre defect indicator (TDI) system renders spare tyre unnecessary.

The M5 is equipped as standard with a tyre pressure warning system comprising the Tyre Defect Indicator (TDI) as well as the second-generation M Mobility System (MMS). This control system warns the driver visually and acoustically in the event of a sudden or gradual pressure loss in one or more tyres as soon as tyre pressure falls below a certain critical value. Due to so-called hump geometry of the rims, even a completely deflated tyre will not jump off of the rim, therefore the driver is still able to safely bring the car to a halt. Following this, MMS is used to seal holes of up to six millimetres in the outer part of the tyre, so that the car can still easily be driven to the next garage. This system facilitates the repair of practically any tyre puncture, without having to change the wheel on the spot. Consequently, there is no need for a spare wheel. Compared with a complete spare wheel, this results in a saving in weight of more than 20 kg, thereby facilitating an improvement in the power-to-weight ratio and driving dynamics.
1 - 1 of 1 Posts