BMW 640i Convertible

It’s always tempting to go for the flagship model when choosing a high-performance car. But what if you look further down the range? We’ve already driven BMW’s new 6-Series Convertible in 401bhp 4.4-litre V8 650i trim – so now we see how the 640i stacks up.

Its turbocharged 3.0-litre straight six-cylinder engine offers 320bhp and 450Nm of torque from only 1,300rpm. And that means strong performance. The benchmark 0-62mph sprint takes 5.7 seconds – seven-tenths down on the 650i – while top speed is electronically limited to 155mph. 

Under full throttle, there’s a distinctive straight-six howl, and the unit provides deep reserves of punch for overtaking. But the whole experience is smooth and refined, thanks in part to the superb eight-speed auto box.

It costs around £8,000 less, and is also cheaper to run. The 640i features EfficientDynamics technology, with stop-start and active aerodynamics helping it return 35.8mpg combined and emit 185g/km of CO2. In contrast, the 650i posts 26.4mpg and 249g/km. Adaptive dampers and four-wheel steering ensure it feels much more nimble than a car of this size should. And while the ride is firm, it remains compliant, even on 19-inch alloys. The electrically operated fabric roof folds in 19 seconds (or rises into place in 24 seconds) – a process that can be carried out at up to 25mph.

Plus, refinement is good top up or down, especially with the optional wind deflector. 

Inside, the dashboard remains angled towards the driver and many of the car’s functions are controlled via the iDrive dial. The seats provide a wide range of adjustment and owners can choose from an array of options, including a full-colour head-up display system for the first time. 

The rear seats are suitable only for children, and the boot could have a wider and more practical opening. However,it’s a desirable machine, and the best in the range so far.

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