2007 BMW M6

Servotronic steering with two effort levels

Like the ’06 7, 6 and 5 Series, the M6’s rack-and-pinion steering system has Servotronic vehicle-speed-sensitive power assist.

Also, the steering ratio – the number of degrees the steering wheel must be turned to steer the front wheels by 1 degree – is variable; the ratio gradually becomes “quicker” (greater steering angle relative to steering-wheel turns) as the steering wheel is turned away from its center position. This is not BMW’s Active Steering, which varies the steering ratio more widely and does so in response to vehicle speed; instead, BMW M chose to tailor the 6 Series’ “standard” steering system to the attributes of this ultimate sports coupe.

But variable ratio and Servotronic assist aren’t all that’s special. The M6 also offers the driver a choice of two levels of assist: Comfort, with typical BMW assist, and Sport, with less assist for sportier feel. Within these two settings, Servotronic varies the assist according to vehicle speed.

Immensely powerful, fade-resistant compound, cross-drilled brakes
To match its colossal performance, the M6 gets immensely dimensioned ventilated disc brakes. At the front, they are 374 mm/14.7 in. in diameter and 36 mm/1.42 in. thick, compared with the 650i’s already generous 348 x 30 mm. At the rear, they’re 370 mm/14.6 in. in diameter and 24 mm/0.94 in. thick (650i: 345 x 24). But the M6 goes further, with compound brakes.

This most elaborate of BMW brake concepts, also appearing on the M3 with Competition Package and the M5, shares 2-piece rotors with the 6 Series: an aluminum “hat” inner portion to reduce unsprung weight, and a cast-iron outer portion as the actual friction surface). But whereas on those models the hat and outer portion are riveted together, here the hat and outer portion are connected by steel pins on which the aluminum and cast-iron portions, because of their differing expansion rates, can move relative to each other.

The 6 Series’ aluminum/cast-iron rotors cut unsprung weight, and reduce rotor deformation under hard-braking, high-heat conditions by about 20%. This construction is more elaborate and costlier. It saves an equal weight proportion, and totally eliminates deformation. This means virtually no tendency of the brakes to vibrate when red-hot, and virtually no likelihood of the rotors cracking even under the extreme temperatures that might be encountered in driving on a racetrack.

Additionally, the M6 brake rotors – again, as on the M3 Coupe with Competition Package and the M5 – are cross-drilled to enhance heat dissipation beyond that provided by the rotors’ internal ventilation; this further enhances fade resistance. It also reduces weight – unsprung weight – by a full 1.5 kg/3.3 lb. per rotor. The front calipers have dual pistons, another M6 upgrade; front and rear calipers – highly visible through the wheels – are finished in glossy black.

Thus the M6 incorporates BMW’s most capable braking system. It is one of the many reasons why the M6 is a truly track-ready car.

Wheels and tires: ultimate grip and style

In its wheel-tire equipment, the M6 takes the 6 Series platform to its ultimate level of performance and style. The wheels, in a very open, discreetly aggressive M Double Spoke design, are sized 19 x 8.5 front/19 x 9.5 rear and carry 255/40ZR-19 front / 285/35ZR-19 high-performance tires , specially developed for the M5 and M6. Though both are designated M Double Spoke, the actual wheel designs differ: the M5 has 10 double spokes, the M6 five.

These are not run-flat tires; there are no run-flats yet that meet BMW M parameters of speed rating and weight. The regular-production 6 Series does come with run-flats and has no provision for a spare tire, so the M6 is equipped with the M Mobility System.

If a tire is punctured – a rare event in any case – the M Mobility System provides for temporary repair and inflation of the damaged tire. Should a tire ever be completely destroyed, BMW Roadside Assistance is available for the life of the vehicle.

Specially calibrated, variable Dynamic Stability Control

DSC is standard on all BMW models; on all current M models, this electronic traction and stability system complements the M Variable Differential Lock.

DSC optimizes traction by electronic means. In cooperation with supplier Continental Teves, BMW M engineers have developed specific DSC logic that, together with the fast-responding engine, performance-oriented gearing and differential lock, achieves traction enhancement in an M-compatible way…in other words, without undue interference with M6 performance and the differential lock’s ability to get M power to the road. With M-calibrated DSC and the differential lock at work, the M6 can master virtually any traction situation.

The M6’s DSC also includes some new functions recently added to other Series:

• Brake Standby. When the driver lifts off the throttle pedal abruptly, DSC senses that sharp braking may be about to occur and applies just enough pressure to snug up the pads against the rotors. Thus by the time the driver’s foot reaches the brake pedal, the short lag from bringing the pad to the rotor is eliminated; this can reduce the stopping or deceleration distance.
• Brake Drying. Acting on input from the windshield wipers’ rain sensor, the pads are periodically brought up to the rotors – just enough to eliminate any film of water between pads and rotors, but not enough to cause any brake application.

As usual, DSC can be de-activated by the driver. Like the M5, the M6 DSC takes on a unique dimension by offering an M Dynamic Mode. Activated by the DSC console button, this mode allows more oversteer and wheelspin, useful to an expert driver on a race track. It is not recommended for use on public roads.

M Variable Differential Lock: ...

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