BMW Australia has introduced a longer, wider and lower new open-top flagship in the second-generation 6 Series Convertible, which this time round beats the redesigned 6 Series Coupe to market by almost a year.

Due to make its global production debut at the Shanghai motor show tomorrow (April 19), the third-generation 6 Series Coupe is due on sale here around the same time as the all-new M5 super-sedan – which will emerge in concept form at Shanghai – in the first quarter of 2012.

Of course, there will also be eventual replacements for the outgoing M6 Coupe and Convertible, as well as the addition next year of the first 6 Series sedan, based on the recent Gran Coupe concept.

From May 29, however, the first all-new 6 Series Convertible since the original went on sale here simultaneously with the coupe in May 2004 will be available in just one model specification, though with a choice of engines.

Priced $3200 higher than the model it replaces at $248,300 plus on-road costs, the twin-turbo V8-powered 650i Convertible comes loaded with a host of ConnectedDrive and EfficientDynamics technologies.

It will receive vital showroom assistance from Australia’s first six-cylinder 6 Series – and the first sub-$200,000 6 series – when the 640i arrives later than expected in August following a production delay, powered by a turbocharged petrol engine and priced at $194,300.

As we reported in March, the sharper new entry level pricing makes BMW’s new soft-top more competitive with key rivals like the Mercedes-Benz SL350 ($242,780), Porsche 911 Cabriolet (from $245,300), Jaguar XK Convertible ($247,415) and even Aston Martin’s V8 Vantage Roadster ($274,698).

The availability of two concurrent engine options for the first time in a 6 Series should also provide BMW’s top-shelf two-door with the weapons it needs to reverse its seven-year-old predecessor’s worrying sales slide.

As with all sportscars, the 6 Series has suffered a significant decline in popularity since it was launched, despite regular upgrades in February 2006, December 2007 and November 2009.

BMW has shifted just two 6 Series models in Australia this year compared with 15 in the same period in 2010, when sales were 35 per cent down on 2009 numbers, but that was still enough for a four per cent share of Australia’s top-shelf $200,000-plus sportscar segment.

In 2009, a total of 63 sales for the year gave the 6 Series a 7.7 per cent segment share, which was still well down on the dominant 911, as well as Maserati (all models), Ferrari (all models), the SL and XK.

However, BMW Group Australia managing director Phil Horton said he expected the new two-variant 6 Series Convertible range to outsell its predecessor by conquesting buyers from other brands.

“The 6 Series Convertible is the jewel in the crown of BMW’s open-top performance car offering, and with both models having such high standard specification, it is a particularly compelling value package for Australian customers,” he said.

“We expect this second-generation 6 Series Convertible to lure customers from other exotic marques on the grounds of its blending elegant design and unrivalled performance.”

Like the new 6 Series Coupe, the wheelbase and body of the new 2+2-seater convertible – first seen in production form at the 2010 Los Angeles motor show in November – are some 75mm longer than before, while width is up about 40mm and height reduces by 5mm.

The range-topping 650i’s 4.4-litre ‘TwinPower Turbo’ direct-injection V8 generates 300kW of power and peak torque of 600Nm between 1750 and 4500rpm – enough for it to sprint to 100km/h in a claimed five seconds and return fuel consumption of 10.7L/100km and CO2 emissions of 249g/km on the EU combined cycle.

The 640i’s direct-injection twin-scroll turbocharged 3.0-litre straight six, meantime, offers 235kW and 450Nm (between 1300-4500rpm) and can accelerate to 100km/h in 5.7 seconds. It consumes 7.9L/100km and emits 185g/km.

Both variants come standard with an eight-speed automatic transmission with steering wheel shift paddles, plus idle-stop, active air-vent and brake energy regeneration systems.

Both models also come standard with 19-inch V-Spoke alloy wheels, adaptive headlights, Comfort Access keyless entry/starting, USB/Bluetooth with audio streaming, internet connectivity, adjustable lumbar support, seat heating, Professional navigation, a rear-view camera, front and rear parking sensors, sports seats and BMW’s latest full-colour head-up display.

Also standard is High-Beam Assist, bi-Xenon headlights, cruise control with brake function, LED fog lights and daytime driving lights, Dynamic Driving Control, an alarm, ambient lighting, Dakota leather trim, iDrive infotainment system with 10.2-inch colour screen, a HiFi sound system and interior and exterior metallic paint.

In addition, the 650i adds Adaptive Drive (which combines Dynamic Damper Control and the Dynamic Drive active roll stability system), ‘Comfort’ seats, Surround View, a TV function, a Professional HiFi sound system with 80GB hard-drive and front seat ventilation.

While the four-mode Adaptive Drive system will also be an option on the 640i, both models can be had with Parking Assistant, which automatically identifies parking spaces before parking the vehicle hands-free.

Another BMW first will be the DAB+ digital radio tuner available for both models, while BMW says the 6 Series will be the first in its segment to offer internet functionality and in-car email display via Bluetooth.

The 6 Series Convertible will be available with three soft-top colours – black, beige and a glossy new Anthracite Silver hue – two non-metallic exterior paint colours and seven metallics, including the new Vermillion Red, Havanna and Orion Silver paints.

Complementing the black and ivory white interior colours is the choice of standard Dakota leather trim in black, ivory white or cinnamon brown, and the option of double-stitched Exclusive Nappa leather trim, which also comes in Vermillion Red and also features ‘SunReflective’ technology.

Rounding out the interior cosmetic options are three trim choices – standard brushed aluminium and two wood variants – and ceramic highlights for the gearshifter, climate controls and i-Drive controller surround.

A further option is the choice of active seats instead of the standard new pews, which feature an integrated belt system, ‘easy-entry’ rear-seat access, power adjustment for height, slide, backrest angle and head restraint angle, plus memory positions for both front occupants.

Sports seats are standard on the 640i and a no-cost option in the 650i, in which Comfort seats (optional in the 640i) offer revised head restraints, power lumbar and thigh support, and adjustable backrest width and angle.

While a removable wind deflector is again optional, this time the 6 Series Convertible’s windows (including the rear windows, which fully retract for the first time) can be lifted or lowered via remote control from up to 30 metres away, while the soft-top itself can also be operated within 1.5 metres.

Technical highlights include a flat-screen instrument panel with high-resolution 9.2-inch info display and black-panel technology from the latest 7 Series, electric power steering and a fully automatic multi-layer soft-top that features seam-free lining and can be lowered in 19 seconds and raised in 24 – both at speeds of up to 40km/h.

Naturally, there are also a host of technical options, led by lane-change and lane departure warning systems, which employ two radar sensors at the rear of the car to monitor traffic in adjacent lanes from the blind-spot rearward to a distance of 60 metres.

BMW says the mean body strength of the 6 Series Convertible, which also comes with “world-first” integration of its owner’s manual within the iDrive system, is increased by 29 per cent, while static torsional stiffness is up by 50 per cent.

Weight-saving measures include the fitment of an aluminium bonnet and frameless doors (the latter saving 14kg alone), thermoplastic front quarter panels and Sheet Moulding Compound (SMC) fibreglass composite boot lid and soft-top compartment cover.

Like its upcoming F13-series coupe sibling, the new F12 6 Series Convertible is built at BMW’s Dingolfing plant in Bavaria, alongside the 7 Series limousine and 5 Series Gran Turismo, sedan and wagon.