What is it?
It’s the latest offering from Alpina, the slighly left-field family firm from Bavaria that somehow manages to fettle BMWs without annoying the German colossus. Indeed, the D4 Convertible is built, along with every other Alpina, on the main BMW production line - and that means that it has to slot into a niche that doesn’t really tread on the toes of the mainstream company’s products. Talk about walking a tightrope; Alpina’s 70-odd engineers must surely be matched by a similarly strong, and equally intelligent batch of product planners.
Anyway, it will probably not shock you to read that the D4 Convertible gets the same retuned version of BMW’s N57 straight-six twin-turbodiesel as the D3 saloon and estate and the D4 coupé. It’s not short of heft, then, with 345bhp and 516lb ft of torque - enough for a 0-62mph dash in 5.0sec and a top speed of 171mph. Perhaps more important, that wall of torque is available between just 1500rpm and 3000rpm, giving the D4 potentially great real-world flexibility.
For this you pay a smidge under £55k - which is around 10 grand more than BMW's 435d Convertible.