New BMW Z4 and Z4 M Roadster Unveiled

Press Release

Chassis and Suspension of the new Z4 M Roadster

Driving Pleasure at the Limit

 

With the BMW Z4 Roadster already offering its driver the right kind of sus­pension perfectly set up for sports motoring and raising driving pleasure to the very limit, the BMW Z4 M Roadster goes even further. Quite simply be­cause the guiding principle for every M Car is that the suspension must be even faster than the engine.

All BMW and BMW M Cars are required to comply with one benchmark in living out this guiding principle: their lap times on the Northern Circuit of the legendary Nürburgring arguably the most dynamic race track in the world when it comes to driving dynamics of the highest standard. Indeed, this is where the term “purist driving dynamics� first originated.

How a car “feels�, what feedback it gives the driver through its suspension, steering, brakes, and seats – this interplay of all the car’s components under all driving conditions comes out most clearly on the 20.8-kilometre-long North­ern Circuit. And it is precisely here that the Z4 M Roadster significantly outperforms even the fastest lap times of the BMW M3, clearly proving that this car offers the best overall package in terms of driving dynamics versus the competition.

Optimum Features for a Perfect Suspension.

The chassis and suspension of the Z4 M Roadster is a consistent develop­ment of the suspension already featured on the BMW Z4 – which as such already offers driving qualities acknowledged as the benchmark in the road­ster segment. With all essential components of the Z4’s suspension based on the BMW 3 Series, the Z4 M Roadster originates in its suspension tech­nology from the BMW M3, for example on the rear axle with its M limited-slip differential. And the brake system even comes from the BMW M3 CSL super­sports. In practice, this means that the Z4 M Roadster has all the DNA of BMW’s legendary driving machines with their overwhelming success in motorsport.

The Z4 M Roadster retains the basic geometry of the BMW Z4 Roadster, with front track measuring 1475 millimetres or 58.1´´ and rear track of 1,496 millimetres or 58.9´´. Compared with the “basic� model, the suspension on the Z4 M Roadster is lowered by 10 millimetres or 0.39´´, while wheel guid­ance with its more negative camber meets the highest requirements in driv­ing dynamics and copes with even higher loads.

Well-balanced axle load distribution of almost 50:50, a low centre of gravity as well as rear-wheel drive avoiding even the slightest drive forces on the steering offer optimum conditions for smooth and harmonious motoring, supreme traction and performance, as well as exceptionally high speeds in bends. The very wide track of the car relative to the size of the body, as well as anti-roll bars on both axles, both serve to enhance driving stability, the BMW Z4 M Roadster most probably being the world’s most agile and dy­nam­ic open two-seater in its class.

Specially Developed Front Axle.

The single-joint front axle with its bolted McPherson spring struts is a special development created specifically for the Z4 M Roadster. To reduce unsprung masses to a minimum, the track control arms are made of forged aluminium.

Very stiff, weight-optimised connection of the chassis components to the body of the car ensures a significant improvement of steering and driving pre­cision. The front axle subframe, in turn, accommodates the steering transmission, anti-roll bar, track control arms and tie-bars. Shaped like a large letter “U�, the front subframe is reinforced by a thrust panel made of three-millimetre-thick aluminium and serving to give the entire subframe structure maximum lateral stiffness. This ensures a particularly precise re­sponse, improves the car’s agility to an even higher standard, and feeds dy­namic wheel forces into the body of the car with maximum efficiency. This effectively compensates the forces generated under high lateral accelera­tion, improving both driving dynamics and driving behaviour to an even high­er level.

Featuring separate mounts for the springs and dampers, the front axle sup­ports guarantee precise wheel guidance and efficiently filter out any un­smoothness on the road. The particular geometric configuration chosen serves to reduce wheel angle spread and allows a larger castor angle giving the Z4 M Roadster its superior agility and reliable feedback to the driver, but without in any way neglecting the need for adequate motoring comfort.

Extremely Secure and Stable Rear Axle.

The central arm rear axle featuring twin-sleeve gas pressure dampers and an anti-roll bar is guided by two track control arms and one longitudinal arm. The upper track control arm is made of aluminium, the longitudinal arm is mounted on a central support within the body of the car. A V-bar extending from the rear axle to the floor structure of the body provides an additional stiffening effect. In all, this elaborate structure ensures very safe handling and prevents uncontrolled steering behaviour.

Both the suspension and damping components are firm and sporting in their response. The reduction of body movement amplitudes and sway angles to a minimum gives the driver a safe feeling at the wheel even at race speed. The Z4 M Roadster therefore retains its supreme yaw stability even after load changes in a bend or when applying the brakes on winding roads even at high speeds, without the DSC stability control system being required to intervene. Roll comfort and acoustics are surprisingly good for a roadster with such active driving qualities.

Cutting-Edge Steering Precision.

Unlike the BMW Z4 Roadster, the Z4 M Roadster features hydraulic, not electric, power steering supporting the rack-and-pinion steering system. This allows even higher steering speeds and thus offers benefits when driving to the extreme. And at the same time hydraulic power steering, in combination with M-specific front axle kinematics, ensures optimum feedback to the driver.

Compound High-Performance Brakes to Control M Power.

It goes without saying that an extremely fast car requires extremely good brakes. Precisely this is why the new Z4 M Roadster comes with particularly strong and powerful brakes originally developed for the BMW M3 CSL: a floating compound high-performance brake system. The inner-vented fric­tion ring on the grey-cast iron brake discs is connected in floating arrange­ment with the aluminium brake cover via cast-in stainless steel pins. This significantly reduces thermal tension acting on the brake discs, increasing the service life of the discs accordingly. Perforation of the friction ring serves additionally to reduce the weight of the brake discs by another 0.7 kilograms on each front wheel and 0.8 kilos on each wheel at the rear.

The use of large grey-cast-iron brake discs (diameter/thickness at the front: is 345/28 millimetres (13.6/11.0´´), at the rear 328/20 millimetres (12.9/0.8´´)) allows truly outstanding deceleration and stopping power: Supported by a 10-inch booster, the brake system is able to bring the BMW Z4 M Roadster to a standstill within just 34 metres or 112 feet from a speed of 100 km/h. Clearly, therefore, this supreme roadster stands out impressively even in the segment of top-class sports cars also through its brake performance.

Exclusive Wheel Design.

High-performance 225/45 ZR18 tyres measuring 18 inches in diameter come on 8-inch-wide wheels at the front, together with 255/40 ZR18 tyres fitted on 9-inch-wide wheels at the rear. Both the tyre compounds and dimensions are perfectly suited for conveying a high level of lateral and longitudinal forces to the road both when dry and wet, giving the driver clear feedback on the car’s current driving dynamics.

The special design of the light-alloy rims chosen exclusively for the BMW Z4 M Roadster boasts the double-spoke styling characteristic of BMW M Cars. Indeed, this styling comes directly from the striking design language of the roadster itself, with taut surfaces interacting with precise lines. Through their lightweight look and almost unobstructed visibility to the extra-large disc brakes, the light-alloy rims again accentuate the high-performance qualities of the Z4 M Roadster.

Forget the Risk of a Puncture.

The wheel rims also offer important “inner� values, the special extended hump (EH) geometry of the rims preventing the tyres from slipping into the wheel bed under loss of pressure and maintaining the safe stopping prin­ciple boasted by all M Cars.

Tyre Pressure Warning System Featured as Standard.

Now enhanced to an even higher standard, TPC Tyre Pressure Control per­manently monitors the wheels while moving and triggers an alarm whenever pressure drops to less than 50 per cent of the level required. Even with pres­sure reduced to such a low level, the tyre still remains safely on the wheel thanks to the extended hump rim, enabling the driver to slow down to a halt without the slightest problem.

He is then able to seal holes up to 6 millimetres in diameter by means of the MMS M Mobility System, a mini-compressor and rapid sealant, subse­quent­ly driving to the next workshop without having to change the wheel. With this system making a replacement or emergency wheel unnecessary, the weight saving achieved in this way is more than 20 kilos or 44 lb.

DSC Dynamic Stability Control for Safe Driving Pleasure to the Very Extreme.

Again reflecting BMW’s clear and consistent philosophy, the Z4 M Roadster does not require driving control systems to enhance the – already outstand­ing – suspension, but rather to master critical situations when driving to the limit. This is because, quite simply, M suspension already provides very sig­nificant safety reserves to begin with.

The BMW Z4 M Roadster features the latest generation of DSC Dynamic Stability Control. This very special control system developed by BMW is in­creasingly becoming the key unit integrating the car’s entire electronic con­trol equipment.

DSC with Useful Additional Functions.

Originally, DSC served “only� to apply the brakes specifically on individual wheels in order to enhance driving safety on slippery surfaces –  for example in abrupt manoeuvres or with the car threatening to become unstable in bends. Today DSC offers a far wider range of functions in terms of sporting performance, safety and comfort. Integrated ASC stability control, for exam­ple, limits slip on the drive wheels by taking back the throttle, applying the brakes selectively on a drive wheel about to spin, and therefore re-stabilis­ing the car as required.

A further function of DSC is CBC Cornering Brake Control with its asym­metric brake pressure monitor preventing the car from swerving when applying the brakes slightly upon entering a bend.

In addition, the latest generation of DSC Dynamic Stability Control offers a whole series of other very useful functions such as ongoing Brake Pad Wear Control serving also to calculate the distance the car is still able to cover on the current brake pads and thus helping the driver to organise his next stop for service in good time. Yet a further function is DBC Dynamic Brake Con­trol maximising brake pressure when applying the brakes in an emergency.

DSC with On/Off Function.

The DSC logic control system has been specifically upgraded and extended for the BMW Z4 M Roadster. Spontaneous response of the engine and the short axle transmission ratio, for example, require extremely fast and sensi­tive supervision of both the engine and the brakes. The first necessity is to ensure adequate yaw resistance also on slippery surfaces, while the second requirement is not to excessively reduce the car’s drive power through the variable M differential lock, by no means curtailing the proverbial sheer driving pleasure the driver obviously wishes to enjoy in a BMW and a BMW M Car in particular. And should the driver decide to do without DSC in a spe­cific situation, he is able to completely deactivate the system at the touch of a button.

Differential Lock Replacing DTC.

Instead of DTC Dynamic Traction Control, a sub-function of DSC otherwise featured in the BMW Roadster, the driver of the Z4 M Roadster enjoys the qualities of the variable, speed-sensing M differential lock carried over from the M3 and adjusting the car’s driving behaviour to the even higher level of driving dynamics. This superior system gives the roadster both a high stand­ard of driving stability and optimum traction particularly when accelerating out of a bend.

The most important difference between the M differential lock and DTC is that DTC allows an increase in slip on the rear wheels “only� up to a medium level of lateral dynamics of approximately 70 km/h and/or 0.4 g lateral ac­ce­le­ration. By contrast, the M limited-slip differential builds up a specific lock­ing force on demand, helping the experienced driver who prefers a very sporting style of motoring and providing assistance on roads with an aver­age to high frictional coefficient and thus further enhancing the positive qualities of rear-wheel drive.

M Differential Lock with Enhanced Traction.

On a “normal� torque-sensing limited-slip differential the sum total of all drive forces the car can convey to the road depends on the forces transmitted by the wheel with the lowest frictional coefficient. Should the frictional coefficient on that wheel be very low, for example on snow, such a conventional lock concept provides only very limited traction benefits due to the reduced drive momentum. By contrast, the variable M differential lock offers decisive be­ne­fits in terms of traction even in the most demanding driving situations, that is with extreme differences in the frictional coefficient acting on the drive wheels.

Ample Drive Power in Every Situation.

A further advantage of the M differential lock is that it immediately builds up growing locking action with an increasing difference in speed between the drive wheels. This means that a wheel “relieved� of its usual load, that is the inner wheel in a bend on a fast mountain pass, can no longer completely “interrupt� the flow of drive power – instead, the drive power and momentum required are consistently maintained at all times.

Locking Action up to 100 Per Cent.

The variable M differential lock follows a clear principle: The difference in speed between the drive wheels when one wheel is relieved of load and drive forces or runs on a very slippery surface spontaneously builds up pressure in an integrated shear pump. This pressure is transferred via a piston to a multiple-plate cutch serving, regardless of the difference in wheel rotation, to convey a certain drive force to the wheel with better grip.

Under extreme conditions all the drive force and torque is conveyed to the wheel with the better frictional coefficient. Once the difference in speed bet­ween the two wheels drops again, pump pressure automatically also de­creases and the wheel’s locking action is reduced accordingly.

This self-controlling pump system does not require any maintenance and is filled with highly viscous silicon fluid.

The big advantage for the driver is that he is able to set off much better even on a surface with very different frictional coefficients on the two drive wheels, since he now benefits from more traction. A further point is that the variable M differential lock significantly improves the car’s handling and driv­ing stability, ensuring additional safety and driving pleasure.