Hot on the heels of the latest BMW M3 Saloon and M4 Coupé, both of which were revealed at Detroit at the start of the year, details of the M4 Convertible are now released, the fifth-generation high-performance open-top car of its kind from the company’s M division.
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Powered by the same 431hp in-line six-cylinder engine as the M3 Saloon and M4 Coupé, the Convertible offers the option of a six-speed manual or seven-speed M Double Clutch transmission. The M4 Convertible exhibits all the hallmarks of a car created by BMW’s high-performance specialists – lightweight engineering, carefully honed aerodynamics, advanced race-derived chassis tuning and electronic driver assistance technologies and a sporty elegant profile, open or closed.
The heart of the M4 Convertible: a high-performance TwinPower Turbo engine
The BMW M4 Convertible derives its firepower from a high-revving six-cylinder TwinPower Turbo engine which benefits from technologies developed on the race track. This 2,979cc in-line six-cylinder powerhouse, developed by BMW M, features two mono-scroll turbochargers, high-precision direct injection, VALVETRONIC fully variable valve timing and Double-VANOS variable camshaft control. This technical prowess allows the M4 Convertible to switch seamlessly from an undemanding everyday road car to one which feels totally at home on the race track.
Huge reserves of torque peaking at 550Nm are available from just 1,850rpm – exactly the point at which maximum power of 431hp is attained. This is then maintained until 7,300rpm. Maximum engine revolutions are 7,600rpm. All of this means the M4 Convertible delivers a seemingly never-ending surge from little more than engine tickover to the electronically restricted top speed of 155mph. The zero to 62mph sprint is achieved in 4.6 seconds with the six-speed manual gearbox, or 4.4 seconds with the seven-speed M Double Clutch Transmission.
Such impressive performance calls for advanced, race-derived technologies, including special cooling systems. An indirect intercooler maximises charge pressure and engine output, while the main radiator is supplemented by other coolers located in the sides of the engine bay for the high and low-temperature water circuits as well as for the engine and transmission oil (with the M DCT gearbox). An additional electric coolant pump helps to cool the turbocharger bearing mounts when the car comes to rest.
The lightweight magnesium sump has a special cover to minimise the movement of oil during high-G cornering, and an additional pump and sophisticated oil return system maintain stable oil circulation under hard acceleration and braking.
The iconic quad exhaust system contains electronically controlled flaps which minimise back-pressure and ensure that the M4 Convertible has an unmistakable BMW M sound.
The £2,645 optional seven-speed M Double Clutch Transmission effectively combines two gearboxes, each with its own clutch. Shifts are therefore completed with no interference to the power delivery, enhancing both performance and efficiency. Gear shifting can be fully automatic or via the selector lever or steering column-mounted paddles. Drivelogic allows the driver to choose more sporting or more comfort-oriented shifting programmes while in automatic mode, and the seven-speed M DCT transmission also incorporates Launch Control to ensure the fastest-possible acceleration from standstill.
Lightweight engineering aids performance, agility and efficiency
BMW’s M cars do not achieve their exceptional performance simply through brute power. Advanced weight-saving technologies and carefully honed aerodynamics also play a major part while assisting agility and efficiency.
The M4 Convertible is around 60kg lighter than the outgoing M3 Convertible, despite being more lavishly equipped. A low kerb weight of 1,750kg, has been achieved through extensive use of aluminium for the bonnet, front wings and many of the chassis components, while carbon-fibre reinforced plastic (CFRP) is used for the propeller shaft and strut brace in the engine compartment. CFRP is light but extremely strong: the single-piece propeller shaft is 40 percent lighter than the steel one in the M3 Convertible, reducing rotating masses and improving powertrain response. The engine compartment strut brace weighs just 1.5kg, yet aids more superior body control than with an aluminium strut.
The M4 Convertible has a number of special aerodynamic measures to achieve the downforce required of a high-performance car while adding to the comfort of its four occupants and overall efficiency during everyday road use. The dynamically shaped front apron, a smooth underbody and special airflow channelling through the front end all help to counter lift at speed. Meanwhile, the Aero Curtains and M side gills with integral Air Breathers behind the front wheels are instrumental in reducing drag. Even the twin-stalk door mirrors help the M4 Convertible cut through the air better.
As a result, the M4 Convertible’s high performance is balanced by its low fuel consumption and CO2 emissions. In manual form the new model is capable of 31mpg with CO2 emissions of 213g/km, while with the quick-shifting seven-speed M Double Clutch Transmission these improve to 32.5mpg and 203g/km CO2.
Like all BMWs, the M4 Convertible is equipped with a suite of EfficientDynamics fuel-saving technologies, including Auto Start-Stop, Optimum Shift Indicator (in manual mode only with the M DCT transmission), Brake Energy Regeneration, on-demand operation of ancillary units, a map-controlled oil pump and a final drive with optimised warm-up behaviour.
Sports-tuned chassis and electronic driver assistance systems
The race-derived know-how of BMW’s M division also comes to the fore in the tuning of the chassis and its electronic driver assistance features. The result is a car which feels equally at home on road and track.
It begins with the M-specific set-up of the double-joint spring strut suspension at the front and the aluminium five-link axle at the rear. A variable electro-mechanical rack and pinion steering system delivers the seemingly impossible combination of maximum steering precision, response, assistance and fuel efficiency. The integrated M Servotronic system moderates the degree of assistance according to speed, and the driver is able to select COMFORT, SPORT and SPORT+ modes at the touch of a button for even greater personalisation. The M4 Convertible is fitted as standard with BMW M Compound brakes for maximum stopping power, fade resistance and low weight.
The mechanical elements of the chassis are supported by advanced driver assistance systems tuned specifically for the M4 Convertible. A standard feature is the Active M Differential to enhance traction and directional stability, particularly when accelerating hard out of corners. An electronically controlled multi-plate limited slip differential linked to the DSC (Dynamic Stability Control) system assesses accelerator position, wheel rotational speed and car yaw rate to decide how much rear axle lock, up to 100 percent, to introduce.
The DSC system includes anti-lock brakes (ABS) and M Dynamic Mode. Other standard stability support features include Cornering Brake Control (CBC), Dynamic Brake Control (DBC), Brake drying and Hill-start Assistant. In the UK the M4 Convertible will also be fitted as standard with Adaptive M suspension with COMFORT, SPORT and SPORT+ modes.
An added sense of style with greater space and refinement
The dynamic lines of the M4 Convertible instantly mark it out as the high-performance flagship of the new BMW 4 Series Convertible range, while occupants are now treated to greater interior and luggage space and superior refinement.
The wheelbase and width have been increased compared with the M3 Convertible, without disturbing the balanced proportions of a long bonnet, short overhangs and set-back glasshouse – all BMW essentials. Stand-out M design touches include a powerdome in the bonnet, a sculpted front apron with three air intakes and a black double-slat kidney grille. Standard 19-inch M double-spoke light alloy wheels in the UK, flared front and rear wheel arches, M side gills and Air Breathers behind the front wheels and polished slanting quad exhaust tailpipes, make the BMW M4 Convertible a striking M car.
The three-part metal roof now provides significantly improved noise insulation – up to 2dB quieter – as a result of a new headlining which also contributes towards higher levels of winter warmth and comfort. The M4 Convertible switches from a stylish coupé, unencumbered by B-pillars, to an elegant convertible free of obstructive roll-over protection or aerials in 20 seconds. Making all-weather top-down driving a greater pleasure than ever, a wider wind deflector and new three-stage neck-warming Air Collar in the front seats are also available.
The roll-over hoops for the two rear seats are now neatly hidden behind the headrests. In the event of a sudden shower the roof can be raised at speeds of up to 8mph. An innovative new Loading-aid raises the folded roof when it is stowed in the boot to give owners access to their belongings in just 6 seconds. The luggage capacity has also increased to 370litres when the roof is closed and 220litres when it is stowed.
The interior features a number of M division highlights, led by electrically-adjustable, heated and contoured leather M seats with recessed head restraints and integrated seatbelt. The front head restraints incorporate an illuminated BMW M logo. Interior highlights also include an M steering wheel, chrome trim and three-colour M stitching. The individual rear seats offer a combination of comfort and lateral support befitting the car-for-all-conditions character of the M4 Convertible.
The BMW M4 Convertible in the UK
The BMW M4 Convertible will be offered with an extensive specification in the UK. Standard equipment, in addition to Adaptive M suspension and 19-inch M light alloy wheels, will include the BMW Professional media package, upgraded Bluetooth and USB, front and rear Park Distance Control, Folding exterior mirrors and heated front seats. The BMW M4 Convertible goes on sale in the UK on 6 September 2014, priced at £60,730 OTR.