BMW has abandoned its traditional launch approach with the third-generation 6-series by introducing the soft-top version of the new two-door before the successor to the fixed-head coupé.

Pictured here officially for the first time, ahead of a public premiere at the Detroit motor show in January, the upmarket convertible is planned to go on sale in the UK in March, six months before the new 6-series coupé is set to reach local BMW showrooms.

See the official pics of the new BMW 6-series convertible

The new convertible is a clear evolution of the outgoing model. It carries fresh new styling first revealed on the four-door BMW GranCoupé back in April, plus increased exterior dimensions and a roomier four-seat interior.

It also gets an advanced new multi-layer cloth hood, developed in partnership with German-based roofing specialist Edscha.

The fully automatic structure, which retains the characteristic buttresses that extend back over the bootlid, is claimed to open in just 19sec and close in 24sec.

It is covered by a plastic tonneau cover when lowered to preserve the car’s elegant new lines. The glass rear screen, mounted vertically, can be opened independently of the cloth hood.

Read the full story on BMW Concept 6-series

At 4894mm in length, 1894mm in width and 1365mm in height, the new convertible is 74mm longer, 39mm wider and 9mm lower than its predecessor. It also rides on a wheelbase that has been extended by 74mm at 2855mm.

Inside, there’s a more driver-orientated dashboard and centre console than in the old model, and greater leg, head and shoulder room. Luggage capacity remains the same as before, at a nominal 350 litres when the roof is up and 300 litres in open-top guise.

The new 6-series convertible will be launched with the choice of two direct-injection petrol engines in combination with a standard eight-speed automatic gearbox.

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The base model, the 640i, gets a turbocharged 3.0-litre straight six with 320bhp and 332lb ft of torque. It is claimed to hit 62mph in 5.7sec and a maximum of 155mph, while returning 35mpg and CO2 emissions of 185g/km.

Topping the initial line-up will be the 650i. It runs a turbocharged 4.4-litre V8 with 407bhp and 443lb ft, enough for 0-62mph in 5.0sec, but delivers 26mpg and 249g/km.

Other engines will follow, including a 286bhp turbodiesel. Also planned is a successor to the M6 convertible, which eschews the 407bhp naturally aspirated 5.0-litre V10 of today’s model for a version of M division’s new twin-turbo 4.8-litre V8, rumoured to push out in excess of 550bhp.

Greg Kable