It is amazing how easy it is to make a car as inherently cool as the new Mini Cooper Convertible appear utterly ridiculous. You don’t need Carlos Fandango wide wheels, an outsize plastic body kit or zebra-print seats, you just need me.

Large, balding men capable of convincing only themselves that they’re not yet middle-aged look pretty stupid in many cars and rather sad in few more besides. But if you really want a laugh, the sight of me cruising around the south of France in a convertible Mini trying to look as cool as the car would have you smirking quicker than most.

Now I accept that this says rather more about me than it does about a soft-top model from a brand that has been defining youthful transport for 45 years. Nor is it Mini’s fault that, among motoring writers, those fitting the above description outnumber the bright, young and predominately female clientele at whom the car is aimed, by hundreds to one.

Yet its essential rightness is not difficult to see. Widening further the appeal of one of the world’s most coveted small cars by removing its roof was not one of the tougher decisions big business has made of late. The Mini is in such demand that the Oxford factory is at full stretch, churning out 180,000 each year, and now its BMW parent is looking at either expanding the site or building another (not necessarily in the UK) to cope with demand for this and a second Mini model line due towards the end of the decade.

Of the convertibles, 7,000 will be sold in the UK alone between July and the end of the year, of which 4,500 have already been ordered, despite the fact that before last week nobody outside the factory had actually driven one. Its success is as guaranteed as Michael Schumacher’s seventh world championship.

Whether that makes it any good is another matter. Unlike many of those who will buy this car, I can still remember the 1990 Ford Escort pulling off the neat trick of being both the least desirable and bestselling new car in the land. Happily, the Convertible’s merits largely justify the faith placed in it by its legion of adoring fans, even if — as we shall see — a certain something has been lost in the translation.

All three Mini variants — One, Cooper and Cooper S — will be available as drop tops, priced between £13,325 and £17,575, although there are no plans to produce the car in diesel form. We were given access only to the £14,625 mid-range Cooper (a £2,525 rise on the cost of the hard-roofed Cooper) which, like all others, features an electric folding roof.

At the press of a button, the canvas top peels back a foot or so to provide an instant sunroof, but as there is considerable wind buffeting in this mode and it takes only another 10 seconds to fully convert the car, you’re better off pressing the button again and waiting for the roof to detach from the windscreen and fold neatly behind the rear seats. It’s a better solution than the odd-looking arrangement at the back of a Beetle.

Boot space varies between limited and minute according to whether the roof is up or down, but the biggest problem is access through the tiny aperture afforded by the narrow lid. Then again, four centimetres of the already hardly generous rear legroom have been removed to make space for underfloor strengthening, so it’s unlikely you’ll be carrying anyone in the back over long distances. This probably means you will use the rear seat as a luggage overflow.

Like all modern convertibles, the Mini is heavier than its hatchback sister, and if this seems curious, given that fabric weighs less than steel, it is the aforementioned reinforcements that account for its extra 100kg (220lb). Try twisting a shoebox with the lid both on and off and you’ll see why an unsuitably shored-up convertible can soon shake itself to pieces on the road.

And I would have expected BMW’s engineers to have done a better job of it than they have. On typical French country roads I could feel the car’s structure vibrating and the windows creaking much more than I had expected. When the roof is raised, however, the bracing effect of its solid side rails eliminates the problem almost entirely.

One related drawback that was clearly not destined to go away was the Cooper’s breathless performance. It often felt painfully slow, slower even than its 9.8sec 0-62mph time suggests. To me the Cooper badge promises a certain level of performance, and in this one at least, it is a promise left unfulfilled.

So it’s just as well that the Convertible is such a delight in other ways. Its handling appears to have survived the transition relatively unscathed and there’s certainly no comparable convertible I’d rather drive hard, even if its sluggish performance does inevitably take some edge off your enjoyment.

And it’s great simply to potter about in. The cabin is no less than a masterpiece, conferring a class and sense of quality down to the smallest switch that no rival can approach.

The ride is well controlled and comfortable, the new gearbox both slick and quick, and the number of kerbside looks it attracts is simply astonishing.

You just have to hope, in my case, optimistically, that they’re being offered for the right reason.

Overall it seems to me that the Mini has lost more than its roof in its transformation from hatchback to convertible. To an extent this should not be a surprise — convertibles are well-known engineering nightmares and BMW is to be applauded for the design of the roof and the look of the car.

But I was disappointed by its lack of structural stiffness and wonder how little performance can be offered before the once overtly sporting Cooper brand becomes devalued. What remains brilliant about the car is largely that which was bequeathed to it by the breathtakingly clear vision of the original Mini concept. And the scale of that particular achievement can be measured by the fact that, despite my mild disappointment with the Convertible, I’d still choose it over any other direct rival.

Nor do I begrudge it the good fortune of landing itself in such an otherwise underachieving class.

What I would do, though, is somehow find the extra £2,970 to pay for the Cooper S version. With 170bhp instead of 115bhp and a 0-62mph time of just 7.4sec, it seems likely to offer the drive to match its looks, something the Cooper Convertible fails to achieve. It won’t be on sale until August, but I have the distinct feeling that — of them all — it’s going to be the one worth waiting for.