BMW's Clever Convertible

There are still many BMW aficionados who have not accepted new chief vehicle designer Chris Bangle's style, but the recently unveiled 6-Series Convertible will go a long way to improving customer relations.

Sure, it's a fairly slinky convertible, sits on 18-inch alloys and sports dual exhausts, making for a very purposeful-looking ride with the top down, but perhaps the most intriguing exterior design aspect is that of the side fin roof, and for this Bangle deserves a pat on the back.

The two-door 6-Series Convertible is BMW's answer to Mercedes highly-regarded SL-Class roadsters, and the Beemer in question - the 645Ci Convertible - will be a good match for the Merc SL500.

Both cars pack V8 engines, are rear-wheel drive, and offer similar performance, but the Mercedes has a metal-folding roof, which the BMW does not.

This won't be a huge concern for the folks at Bavarian Motor Works, because if you take a close look at the photo with the roof up, you'll notice that towards the rear the cloth roof splits into two fins, giving the 6-Series drop top some serious style.

These fins give the tapered roof a more integrated look, acting as pseudo C-pillars if you like, paying homage to the 6-Series Coupe.

A heated glass rear windscreen is recessed between these 'fins', lending the car a very original and indeed striking appearance, and one that could be bad news for Mercedes, a company that prides itself on trend-setting.

Furthermore, the glass rear window can be fully retracted into the luggage area with the roof both open and closed.

When the roof is up and the rear window is down, the fins ventilate the air around the opening, creating a unique and virtually draught free airflow when driving.

In addition, the folding roof system of the 6-Series Convertible brings other innovations to the table, including an extra layer in the cloth roof lining made of PUR plastic.

This sits between the inner lining and the rubber-bonded outer layer that drastically reduces outside noise and better protects occupants from extreme temperatures.

The cloth roof is fully automated in operation, and can be activated up to speeds of 32km/h (20mph), but BMW won't give specifics on folding time, saying "the soft top disappears completely within a matter of seconds."

On the performance side of the equation, BMW's 645Ci appears to have the edge over the SL500, with more power and torque than the Mercedes tin-top.

While both cars have a limited top speed of 250km/h, BMW reckons the 645Ci will complete the all-important 0-100km/h sprint in 6.1 seconds, while the older SL500 will reach the same speed in 6.2 seconds.

This could be put down to the more technologically sophisticated engine found in the Beemer - it makes use of adjustable length intake manifolds plus variable valve lift (ValveTronic) and valve timing (bi-Vanos).

As such, BMW's 32-valve, DOHC 4.4-litre V8 churns out 245kW @ 5500rpm, while Mercedes' 24-valve, SOHC V8 mill - bigger by some 600cc - outputs 225kW @ 5600rpm.

Total mass may also be a factor in the 0-100km/h times, as the 645Ci tips the scales at 1815kg, while the Merc records an 1845kg kerb weight.

Where the SL500's larger mill comes into play however, is in terms of torque - it makes 10Nm more than the Beemer, which is 450Nm @ 3600rpm, compared to the Merc's 460 Newton metres.

Aiding in the transfer of power from the convertible's crankshaft to the rear hoops are three gearbox options, all of them offering six ratios. There's a traditional manual transmission, a six-speed automatic with Steptronic, and lastly an SMG transmission with gearshift lever and steering wheel-mounted paddles.

Despite losing torsional rigidity to its hard top cousin, BMW wanted to endow the 645Ci with at least a modicum of on-road agility, and Active Roll Stabilisation (ARS) is one way to do this, by reducing body roll and pitch.

There's also a Sport Package available for the new 6-Series Convertible that brings with it Active Steering, which works in tandem with DSC (Dynamic Stability Control) and yaw rate control.

The Sport Package also includes 19-inch alloys with super sticky rubber, tighter suspension and sports seats, while a sportier steering wheel rounds out the upgrade.

On top of its impressive drivetrain and next-generation 'finned' roof, BMW promises that rear seat occupants will be taken care of too, something that few modern convertibles truly offer.

With the obligatory leather upholstery, rear seat passengers are treated to good levels of headroom, thanks to roof's design, and they won't have to step over seatbelts either, as these items are integrated into the front seats.

As well as seating four in relative comfort, the 645Ci has a fair sized boot and can swallow two golf bags plus a medium suitcase, according to BMW. If true, this would make the new 6-Series Convertible one of the roomier drop tops on the market - and judging by the somewhat incongruous boot 'hump', it's not hard to imagine.

Other standard features of the appealing 645Ci include items such as a DVD-based satellite navigation system. This, along with an 8-speaker stereo and other features, is controlled by BMW's hi-tech, but counter-intuitive and much-maligned iDrive interface.

Optional extras include the HUD, or heads up display as jet fighter pilots call them. The novel idea promotes safety above all else, by projecting all pertinent telemetry, such as road speed, engine revolutions and navigation advice, onto the windscreen, thus enabling drivers to stay focussed on the road, and not the dashboard.

The Mercedes SL500 finally has some serious competition in the form of BMW's intriguing new 645Ci Convertible, and when you factor in the innovative roof, powerful 245kW V8 motor and edgy new look, you can bet Mercedes will be quick to update its SL-Class in order to keep it looking fresh in the face of this promising new competitor.

After the new 6-Series Convertible is officially unveiled in Detroit in early January 2004, it is likely to join the 645Ci Coupe in Australia from May 2004, though final pricing and specifications were not available at the time of writing.

BMW also expects that the combined production availability of the 6-Series is likely to be limited to roughly 180 units for the Australian market.

But obstacles such as these certainly won't hurt the 6-Series in Australia, perhaps even lending it a hand by cranking up the exclusivity factor, and, at the end of the day, Chris Bangle will probably see a drop in offensive emails too. Should be one to watch.