BMW 635d Sport Convertible

What is it?

A BMW 6-series that very few people will buy, though lots of people ought to; a genuinely powerful diesel convertible with impressive economy, excellent refinement, and a great deal else to recommend it.

BMW has slotted the stonking twin-turbo 3.0-litre straight six from the 3-series and 5-series into its boulevard-cruising 6-series Convertible. Even though the engine provides over 280bhp, BMW claims 40.9mpg, so 600 miles between fill-ups should be possible.

What’s it like?

Pretty much the perfect long-distance open-top GT – as long as you don’t mind the looks. The huge surge of torque (428lb ft at 1750rpm) wafts the 635d along with ease and the six-cylinder diesel has got to be one of the most sonorous oil-burners around.

The rest – apart from a few mild mid-life cosmetic tweaks – is standard 6-series fayre. That means solid, secure handling, but not much in the way of sporting agility.

Should I buy one?

If you like the looks and the idea of a 6-series and you pay for your own fuel, yes, without question. However, the Coupe version, which is over £5k cheaper, will probably be the bigger seller. That's because many image-conscious 6-series convertible buyers will automatically be put off by the idea of a diesel engine, no matter how good it is or how much sense it makes.

More fool them we say because, whether it's in the coupe or the cabrio, this incredible oil-burner makes the 635d the best 6-series of the lot.

Matt Rigby