For Class-leading practicality and usability, refinement, mighty powertrain
Against Bland-looking design, lifeless steering, uninvolving handling

BMW’s outgoing 6-series proved that conventionally appealing styling isn’t a prerequisite of success in a luxury grand tourer. With 14,000 examples sold in the UK since 2003, it accounted for an average of 25 per cent of registrations within its class, at times even outselling Jaguar’s seductive XK.

The arrival of the new 6-series completes a cycle of renewal for BMW stretching back three years. With the current 7-series, it released its first car based on a new platform called ‘L6’. Designed to underpin all of the car maker’s large rear-wheel-drive cars, the same platform has also spawned the 5-series Gran Turismo, the latest 5-series saloon/Touring and even the £200k Rolls-Royce Ghost.

So versatile is this platform that it can also serve under the subject of this week’s road test – the all-new 650i Convertible – as well as the 6-series coupé (which arrives in the UK this October) and the Merc-CLS-rivalling 6-series Gran Coupé four-door (which will be launched later still). So can you really take a platform first used for a full-size limo and adapt it to make a convincing open-top GT?

The 6-series convertible has put on 39mm of width (now 1895mm) and 74mm of length (4897mm) in the transition from second to third generation. Its body-in-white is predominantly high-strength steel but has been reinforced in key areas with hot-formed ultra-high-tensile steel and is 50 per cent more torsionally rigid than the previous car’s.

Measures to bolster crash safety include a reinforced floor, sills and B-pillars, an ultra-high-strength windscreen frame and automatically deployed aluminium rollover bars that pop up from behind the rearmost head restraints in the event of a roll.

The doors, bonnet and front axle spring mounts are made of cast aluminium to reduce weight. Other measures include thermoplastic front wings and a tonneau cover and bootlid made of glassfibre composite. Even after those efforts, though, BMW quotes a kerb weight of 2015kg for this eight-cylinder 2+2 – 80kg more than the car it replaces. According to our scales, our test car weighed 2085kg with a full tank of fuel. That’s substantial indeed for a car of this type, but it’s not unprecedented. The Maserati GranCabrio we road tested in 2010 weighed just as much.