Press Release
Chassis
Providing agility and poise to complement performance
Harnessing the power
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Strong lightweight chassis achieves a new peak in BMW's advanced lightweight engineering
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Renowned M differential lock offers reassuring safety net
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Latest DSC system offers MDynamic Mode
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Exclusive 19' M wheel design featuring high performance brakes
So, we have heard that the new BMW M6 features an award-winning technologically advanced new V10 engine as well as a unique high-performance transmission system. But these would be wasted if the car's chassis cannot instantly transfer the generated power to the wheels and the road at the extremes of dynamic driving.
One of the guiding principles when designing an M car has always been that the suspension must be 'faster' than the engine. With such performance under the bonnet of the M6 the engineers at BMW M GmbH had a considerable challenge, but one to which they rose admirably.
The recipe had a good stock as its base. The 'standard' 6 Series chassis presents high torsional rigidity of the bodyshell, well-balanced 50:50 front/rear weight distribution, long wheelbase, wide track, aluminium suspension components front and rear and, of course, rear wheel drive.
Combine the experience garnered from developing the M5 chassis, with a shortened wheelbase and lowered centre of gravity, and it is no surprise that the result is an engineering feast. To be served piping hot.
Front and rear suspension
The familiar BMW double joint strut front axle is made largely of aluminium to reduce unsprung weight.
The use of aluminium and reinforcement of the front axle subframe with a special thrust plate delivers maximum lateral stiffness, poised handling and a smooth ride. Separate bearings on the subframe for suspension and dampers contribute to accurate wheel guidance.
The aluminium subframe also features NACA air intakes (used in aeroplanes and racing cars to reduce drag) to direct cooling air to the gearbox without adversely affecting under body aerodynamics.
The rear axle, which is also made almost entirely of aluminium, is a development of the integral axle of the 6 Series. It was adapted for the needs of the M6's higher demands by fitting additional supports, links and joints to optimise the elastokinematics. For example, rigid links have replaced rubber joints to ensure even more accurate guidance and centring of the wheels.
As on the M5, the M6's final drive has been substantially modified to keep weight down and convey the huge power potential to the rear wheels. Cooling fins on the aluminium differential case have enabled the engineers to reduce rear axle temperatures by 15°C. 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 central bearing.
The drive shafts are lightweight and have a torsionally stiff tubular design to keep moving masses as low as possible.
Steering
The power-assisted steering is controlled by M Servotronic mapping. This means that the assistance is related to both road- and engine-speed, thereby resolving the problem of obtaining a balance between the need for light steering at parking speeds and more 'feel' at speed.
The M6 offers two different M Servotronic maps set to the chosen EDC (Electronic Damper Control) mode. In the sporty EDC mode steering is very direct giving the driver an immediate precise response. The comfort mode has a higher ratio for an easier, more comfortable steering reaction.
A gripping tale: The variable M differential lock
Like the M3 and M5, the M6 features a differential with a variable, torque-sensing differential lock developed by M GmbH. This provides the car with a high level of driving stability and optimal traction, especially when driving out of bends.
Unlike a normal limited slip differential with a 25 or 50 per cent locking capability, the variable M differential lock can, in extreme conditions, provide up to 100 per cent locking. This means that when one of the rear wheels loses traction on a more slippery part of the road, or when the inside wheel spins on very tight bends, the M6's differential will ensure that the drive shafts send the required amount of drive to the wheel that can transmit it to the road.
The system works by either driven rear wheel threatening to lose traction. With one driven wheel running at a different, faster speed, pressure is built up in an integrated shear pump. This pressure is transferred to a multiple-disc clutch, via a piston, where drive forces are directed to the wheel with better grip, as determined by the difference in rotational speed of the wheels. When the difference in rotational speed decreases the locking action diminishes.
The advantages of the variable M differential lock are:
· 0-100 per cent drive force can be delivered to either driven wheel.
· On snow, gravel or ice a conventional torque-sensing differential does not offer enough flexibility. The variable M differential provides a substantial advantage when the driven wheels are subject to greatly varying coefficients of friction.
· When combined with a finely tuned DSC system and the near 50/50 weight distribution, this differential lock helps the M6 to excel in very slippery conditions.
· The system delivers rewarding handling on roads with average to high frictional coefficients.
Only on M: DSC with MDynamic Mode
A new generation of Dynamic Stability Control was developed exclusively for 2005's new M models.
As on all BMWs, the M5 and M6 DSC system offers two-stage programming. However, the driver of an M5 or M6 is able to explore the limits of traction a little further than other BMW owners
The first DSC programme corresponds to that of the typical DSC system found on the 'normal' 5 or 6 Series. This provides a safety net should the physical limits of traction threaten to be exceeded. Engine speed is retarded or brakes applied to inside wheels if traction is being lost, ensuring that the car will be brought back under control.
The second level DSC - the new MDynamic Mode (MDM) - is similar to a 5 or 6 Series Dynamic Traction Control system (DTC), but offers the M driver the opportunity to push the car to its absolute limits.
MDM, a drifter's delight
MDM is engaged via the M button on the steering wheel. In this mode DSC is not activated until the absolute limits of adhesion have been reached. This means that the M6 can reach almost any slip angle the driver wants before cutting in to save the day. Understandably, it should not be used on the public road.
The driver is informed of MDynamic Mode by the illumination of a light on the driver's instrument cluster marked 'MDM'.
The DSC system on the M5 and M6 can be switched off completely, which also activates another warning light.
EDC - from sportingly firm to comfortable
The M6's Electronic Damper Control (EDC) allows the driver to adjust the suspension's characteristics from sportingly firm to a softer and more comfortable setting. Three settings are available - Comfort, Normal and Sport - and can be set in iDrive via the MDrive Manager and activated through subsequent use of the MDrive button on the steering wheel, or by activating the EDC switch next to the gear lever.
EDC is a continuous and infinitely variable electronic damper control. In 'Normal' mode the damping is automatically adjusted to achieve the optimum balance between 'Comfort' and 'Sport'. In 'Sport' mode the damping is firmer and employs higher damping forces, thereby reducing lift. In 'Comfort' mode EDC produces lower damping forces in favour of greater ride comfort.
EDC facilitates an improvement in body control (roll and sway) that provides a greater element of safety.
Brakes
The penultimate mechanical element in the M6 performance equation is the brakes, which take the same system as on the M5, but apply them to a lighter and faster car to ensure a reliable and predictable braking performance.
Drilled, compound brake discs are standard equipment all round. At the front the discs are 374mm x 36mm while at the rear 370mm x 24mm units are fitted. The perforations in the discs are the result of stringent testing and motorsport experience.
Low weight, aluminium twin-piston sliding callipers substantially reduce unsprung weight and make a further contribution towards agility, safety and motoring comfort.
Whether it is wet or dry the M6 provides powerful and dependable braking properties. When the brakes are applied at 62mph the M6 is stationary in less than 36 metres. From 124mph the braking distance is less than 140 metres.
The brakes, too, feature an on-board diagnostic system for pad wear. A sensor measures wear at specific points and transmits the values to the DSC system. The system then evaluates driving style and pad condition to determine how many miles to go before the pads need changing. The information is used by the Condition-Based Servicing module to determine adequate service intervals and to inform the driver in plenty of time before a trip to the dealer is required.
Wheels and tyres
The final link between the M6 and the road is the wheel and tyre combination. To accommodate the huge brake discs the M6 is equipped with 19-inch diameter cast alloy wheels unique to the car. These are 8.5 inches wide at the front and 9.5 inches at the rear. The visually delicate five contoured double-spoke styling is a design form that reflects the wheel's lightweight engineering. The wheels being, in fact, approximately 1.8 kilogrammes lighter than conventional 19-inch aluminium wheels.
These stunning wheels are shod with tyres specially developed for the 2005 M cars. The compound and dimensions were designed for precise transfer of lateral and longitudinal forces in both wet and dry and offer an amazingly high degree of comfort. They are also 'tuned' to provide valuable driver feedback so that one can 'feel' the limits approaching.
The tyre sizes are 255/40 ZR19 at the front and 285/35 ZR19 at the rear.
Tyre Pressure Warning System
Since there is no spare wheel and tyre, the M6 is equipped with a Tyre Pressure Warning System (TPWS) and a second generation M Mobility System (MMS).
The warning system provides visual and acoustic warnings as soon as a tyre's pressure falls below a certain critical value. Due to the geometry of the rims, even a completely deflated tyre will not jump off the rim, so the M6 can be brought safely to a halt.
The MMS has become a tried and trusted tradition on M models since the M Roadster in the late 1990's. It uses a sealant that can seal holes of up to six millimetres in length thereby enabling the car to be taken to the nearest garage. The system can repair almost any type of puncture without having to change the wheel on the spot.
Consequently there is no need for a spare that results in a weight saving of more than 20kgs and brings the attendant benefit of power to weight ratio and driving dynamics, along with added storage space.
