Just as BMW had reached a corporate image plateau in 2002-something odd happened. The launch of the 7-series gave the world its first glance of the new BMW vision of Chris Bangle, famous for the Fiat Coupe. This was possibly the most controversial point in the design history of BMW, and has caused a huge backlash amongst once loyal fans. There's even an online petition for him to be fired.

And now BMW has just revealed details of the 6-series Convertible that will appear at the NAIAS, Detroit in January. The 6-series is the fourth production BMW to be adorned with Bangle's new look, and similarly to the Aston Martin DB9 the convertible was developed alongside its hard-top sister, helping to achieve the near 50:50 weight distribution. Aesthetically the styling is as controversial as ever, with Bangle's trademark 'splines' and 'flame-surfaces'. The convertible is more handsome than the coupé with a sleeker side profile, and with the hood down, a lighter, slightly more delicate stance.

The Convertible shares its 4.4-litre V8 engine with the 645Ci coupé, which produces 333 bhp, 332 lb.ft of torque and is capable of propelling the car to 62 mph in 6.1 seconds (6.2 for the automatic). Not an unimpressive figure considering the car weighs 1815 kg. Top-speed is restricted to 155 mph, which is achievable in both 5th and 6th gears. Removal of the restrictor would seem to be a worthwhile exercise (Ahem, if you live near an autobahn - Ed)! Optimal performance is achieved with the help of variable valve timing (BI-VANOS), valve lift control (Valvetronic) and a variable intake manifold.

Three six-speed gearbox variants are available, the standard choice being the manual. Optional choices are either the six-speed automatic with steptronic, or the Sequential Manual Gearbox (SMG), with 'up' and 'down' shift buttons mounted on the leather sports-steering wheel.

The 6-series features Active Steering and Dynamic Stability Control (DSC) to enhance the car's safety and stability. The Active Steering is assisted by an electric motor at low-speeds for improved manoeuvrability, with assistance decreasing as the car gains speed. The system makes use of the DSC to create subtle steering corrections to help prevent oversteer under hard cornering. Whether or not this is successful will only be possible to tell having driven the car - in many older cars this sort of technology feels horribly intrusive, but recently manufacturers have begun to carry it off very successfully. It's possible to raise the DSC limits using the Dynamic Traction Control (DTC), and for the more extreme drivers, DSC can be fully disengaged anyhow. More technical wizardry can be found with BMW's Dynamic drive – a system of stepper motors that build up counter forces on the anti roll bars to decrease roll under heavy cornering.

The roof is reminiscent of a Ferrari hood, and contains a noise and heat-insulating layer to offer as much isolation from the outside world as is possible in a soft-top. It is operated electrically from a button on the dashboard, stowing away in about 20 seconds. It can be raised or lowered while the car is moving at speeds of up to 20 mph, and when down is concealed under a solid cover, standing very slightly proud of the boot-level.

The car has been carefully designed to minimise wind ingress with the roof lowered, and BMW claim that even well in excess of 100 mph the front passengers experience little turbulence. The rear heated window is glass, and retracts electrically into the bulkhead. It can be operated independently of the roof, offering increased ventilation with the roof up, or acting as a wind deflector when the car's in open-top mode. The boot has a 350 litre capacity of which 50 litres is removed when the roof is lowered.

Ample room is available for back-seat passengers: the roof is thinner than a metal top, and offers reasonable headroom. The two front-seats have Easy Access to reduce contortions while climbing into the back, and the front seatbelts are integrated into the seats to further simplify matters.

As with the coupé, the Convertible has toys aplenty. The optional Head-up Display projects information such as current speed, navigation instructions and feedback from the Check/Control system directly into the driver's line of vision, seemingly on the road ahead. Other gadgets include DVD satnav, Adaptive Headlamps, voice activated iDrive and Brake Force Display (under hard braking an extra cluster of lights illuminates to alert drivers following the car).

The 645Ci Convertible will be priced at £55,355 on-the-road for the manual and £56,705 for the automatic. It goes on sale in the UK from March 2004 alongside the coupé.

Adam Jefferson - 18 Dec 2003