There is something truly fascinating about watching a large metal roof unhinge, separate, fold and stow itself. It’s satisfyingly co-ordinated, like some mechanical cardsharp cutting and shuffling a deck, and the new 3-series Convertible’s 22-second performance is no exception.

However, what strikes me about four-seater convertibles with metal roofs is that they nearly always look better with the roof up. The Mégane Coupé-Cabriolet, Eos and 307 CC are all quite svelt machines when they’re protecting their occupants from the elemental onslaught, but put the roof down and it all gets a bit ungainly. They all have rear decks longer than the HMS Ark Royal, accompanied by a slightly hunched look, a bit like they’re wearing a hoody under a jumper.

Now, I realise that if you don’t live in Arizona (the launch venue) then you will spend 90 per cent of your time with the roof up anyway. However, I would also imagine that the entire reason for buying a convertible would be to look good the ten per cent of the time when the sun is out and you can swan around with your pasty complexion on display. Otherwise you’d just buy a coupe, surely.

Thankfully, the new 3-series Convertible bucks the trend. It looks fantastic with its metal roof down. No wedgy, rising waistline. No helipad on the rear. No ludicrously long A-pillars. Just a truly stylish convertible. OK, so roof-up it’s less successful, looking a bit like it’s just got a one-piece hard-top plonked on. But we’ll ignore that minor detail.

This particular car is the 335i, which means it’s fitted with BMW’s remarkable twin-turbo 3-litre straight-six. It’s the most fantastically flexible engine, providing enough growling low-down punch to let you blow pretty much anything away without ever straying above 4000rpm. Yet find a good bit of road and it’s equally rewarding when extended all the way to the red line.

Most buyers will, I suspect, mate it with the six-speed automatic. And they’ll be very happy, because it’s impressively smooth and refined. They’ll almost certainly be pleased with the optional Active Steering, too. But they really should get a manual and be prepared to twirl the wheel a little more, because the manual ‘box is one of the sweetest you’ll ever use. It makes the 335 come alive, while the standard steering shows just what the active system is still lacking in detailed feedback.

Most of Arizona seems to be suited to the automatic version of the car, wide roads with corners designed for wallowing pick-ups the size of Berkshire not really taxing the 3-series.

But roof-down I’m treated to wonderfully unobscured views of the forests of 50-foot-tall saguaro cactuses, along with such delights as a café proclaiming to have ‘The World’s Smallest Museum’ and a town called Superior that definitely wasn’t.

Without the (optional) wind deflector in place there’s more hair ruffling than you might expect, so I should avoid travelling a long way four-up with the roof down. There’s also quite a bit of shake through the steering over small surface imperfections. So much so, in fact, that I might have given the Convertible a whole star less if I hadn’t found a very different sort of road at the end of the day…

Just as the immaculate, graded blue sky begins to turn orange at its base as though it were blotting-paper soaking up the red sand, the road turns tight and twists off through the desert. And the 3-series comes alive. Despite its 195 extra kilos and the shake through the steering, the 335 is still beautifully balanced. You can get it moving through the corner, drifting across the surface with all the sublime adjustability your hands and right foot can muster. It’s wonderfully satisfying.

I can’t see M Division wanting to adopt a folding hard-top, but with the 335 providing all the dynamism most convertible buyers will ever need, perhaps they won’t need an M3 convertible anyway.