Revealed: BMW's new ruthless Grand Tourer

BMW's first genuine cabriolet in half-a-century is far more responsive and sporty than Tom Stewart imagined a car of this type had any right to be

Sometimes the mind plays tricks on you. Like me, I guess you'd have supposed that big, prestige 2+2 soft-tops in similar vein to this new 645Ci Convertible would have featured in BMW's past model line-ups. Without giving it too much thought, I'd have bet money on it.

But before you slap a tenner on the table, the Zs 1, 3, 4 and 8 don't count because they're all two-seater roadsters. None of the 3-Series convertibles qualify either, despite some being reasonably luxurious 2+2s. The 3-Series, M3 included, lacks genuine upmarket positioning. And looking back, there was never an 8-Series convertible, nor any open 6 Series or 3.0 CS/CSi/CSL coupés, nor even any drop-top 2800 or 2000 CS Coupés, and that takes us all the way back to the mid-Sixties.

No, this is a niche market served most loyally in recent decades by the likes of Aston Martin, Bentley, Mercedes-Benz and Rolls-Royce, not forgetting Triumph's inspired Stag of course, as well as a legion of big convertibles hailing from Detroit. And, strictly speaking, Jaguar and Porsche also remain pretenders because their so-called 2+2s would better be described as 2+(0.5+0.5)s.

We have to travel right back to the late Fifties before we find a big, classy cabrio bearing the blue-and-white propellor logo. Very limited numbers of two- and four-seater convertible versions of the V8-powered 503 were sold but, before you make a lunge for my tenner, I have to tell you that these weren't actually built by BMW, but by nearby coachbuilder Baur.

So, somewhat surprisingly, the 645Ci Convertible is BMW's first foray into the prestige 2+2 sector in modern times and, with just one reservation, it's surely a winner. First and foremost, BMW hails the new 6-Series both as a luxurious Grand Tourer as well as being able to provide an enthusiastic driver's adrenal glands with a good workout; it's for the owner to decide which of these dispositions he or she prefers.

Now while this might sound like marketing claptrap I can assure you this is one claim I believe to be true. With a 333bhp, 4.4-litre V8 (already in service in the 5 and 7 Series), you'd rightly expect the car to be a svelte gentlemen's express. I haven't yet had the privilege of a long trip in this car, but deliver I'm sure it shall.

What did raise an eyebrow in surprise was just how responsive and sporty the 645Ci is to drive. Steering response, with or without the optional Active Steering system, is far closer to racer than limo, while even a light foot on the drive-by-wire throttle has the car surging forward with startling immediacy, and that's without resorting to any improved-response Sport mode assistance. This throttle requires more than a half-measure of self control. Fortunately there are brakes to match.

While some soft-top versions of more torsionally rigid hardtop coupés can be a bit wobbly, this isn't the case here. BMW developed the 6 convertible at the same time as, not after, the 6 coupé (they go on sale simultaneously this month) and under the skin there are significant structural differences to maintain the open car's body and chassis rigidity, not the least of many is a lighter, high-aluminium content front end and massive alloy reinforcement just aft of the passenger compartment.

Together with six hydraulic pumps to power the roof (a 20-second operation either way) and pop-up rear roll-over bars this does all add a bit of weight, but BMW asserts that the Convertible is still 20 per cent lighter than the norm, and from the driver's seat it's effectively indistinguishable from the hardtop.

That said, I didn't go hammering over rough Belgian pavé -- my drive, though fast, was smooth -- but I can't pretend the Convertible's cloth top is quite as quiet as the coupé's metal roof. At speed you can hear the wind as it whooshes faintly overhead, but at least with the top lowered you can better hear the big V8's beefy exhaust note. And should it be necessary, the roof can be raised or lowered while driving at up to 20mph.

At the touch of another button the rear glass screen can also be lowered. With the roof up this provides extra interior airflow, while with the glass up it acts as a wind deflector for rear seat passengers when the roof is down. And these passengers, incidentally, needn't necessarily be children; adults will also be perfectly comfortable in the rear. An additional deflector for front seat occupants is stowed in the decently proportioned boot.

Which leads to my one reservation: the boot lid. Although the audio, communication and navigation aerials are ingeniously sandwiched between its two duroplastic layers, the lid is an awkward-looking thing which appears to have been designed for a different car.

Much comment has already been passed about chief designer Chris Bangle's controversial work and I'll not add to it here, except to say in his defence that the huge number of Bangle BMWs sold worldwide comfortably outnumbers the 9,300 or so who have so far signed the "Stop Chris Bangle" online petition.

This may be BMW's first prestige 2+2 convertible in 50 years, and you may not think it quite the prettiest available for £55,355, but the 645Ci Convertible is sportier than you might imagine and ruthlessly virtuous in every other respect.