Appropriately enough, most of the differences between the standard smart roadster and the £16,695 Brabus version are cosmetic. If you're smart about smarts you'll be able to spot a Brabus at a hundred paces thanks to its revised radiator grille, front and rear spoilers, side skirts and 17" alloy wheels. Occasional branding and the use of leather and aluminium make the interior visually distinct from that of the standard model too.But the Brabus modifications aren't all for show. The celebrated German tuning company has also been put to work on the dirty bits, with the result that maximum power shoots up from 80bhp to 101bhp - a hearty figure for a production 698cc engine even when you take the turbocharger into account.Straightline performance is improved, of course, but perhaps not to quite the extent that either those figures or the more purposeful exhaust note might suggest. The official 0-62mph acceleration figure is reduced by a fairly modest 1.1 seconds to 9.8, and that's a more telling statistic than the increase in maximum speed from 109mph to 119mph.Despite all that, this is still the sportiest car in the smart range by an enormous margin, because Brabus has also got its hands on the suspension. This is very good news; here, for the first time, is a smart roadster that is actually as much fun to drive as the concept suggested it should have been all along.I first drove a roadster on the press launch event and then had one for two weeks at the turn of the year (see road test). On each occasion I was dumbfounded that such a light and low-slung car had been made to handle so badly. The most obvious problem was that the suspension was set far too high, and I imagine that's the first thing Brabus decided to change before settling down to revise the spring and damper rates.The effect is startling. Every time I turned any of the standard cars into a corner I felt that it was about to topple sideways, which is the sort of thing that doesn't half make you drive cautiously. From behind the steering wheel the Brabus feels fairly similar, so I had to build up enough nerve to make use of the more composed handling which the paperwork suggested this car must have. Once I'd done that I found the Brabus to be an absolute delight. It zips into corners, settles down very quickly and feels absolutely in control as you feed in the power.In fact, I'll tell you how good the Brabus is. You know the automatic gearbox that's fitted to all three-cylinder smarts? The one we've been complaining about ever since we first tried it because it requires so much effort to make a smooth change? It's fitted here too, but the rest of the driving experience is so enjoyable that I almost didn't mind grappling with the transmission. Not as much as usual, anyway. That's how good the Brabus is.All the cosmetic parts can be specified as options for the standard roadster, though apart from the perceived styling benefits all they will really do is make that car slower, heavier and less economical (one possible exception is the rear spoiler - apparently a smart employee has fitted that to his roadster and found that it improves the handling, though I can only report this as hearsay). You can't buy the standard car with the 101bhp engine, which is possibly just as well because it's quite alarming enough in its less powerful form.Unfortunately, it is also impossible - unless you buy two cars and switch the parts across at enormous expense - to have a standard-weight roadster with the Brabus suspension. This is a great pity because, frankly, the suspension should be available on all the roadsters. As it is, the only way you can buy a roadster that handles properly is to spend nearly £17,000 on it.I realise that smart's great strength as a brand is its unique visual appeal, so what I'm about to say may not be relevant to most customers. But. Standard roadster, no cosmetic gubbins, Brabus engine and suspension. Great car. Not being built. Lost opportunity. Pity.One final point: Brabus has also performed its magic on the roadster-coupé, which in standard form is heavier, has vastly more luggage space, accelerates more slowly, is slightly less economical, reaches a higher top speed (aerodynamic reasons, you know) and costs a bit more, though only to a small extent in each case.Smart quotes identical acceleration and economy figures for the Brabus roadster and roadster-coupé, which can't be right, but the other differences of course match those of the standard versions. The Brabus roadster-coupé is therefore the most expensive car smart builds, on sale at £16,995. Engine 698cc, 3 cylinders Power 101bhp Fuel/CO2 53.3mpg / 126g/km Acceleration 0-62mph: 9.8 seconds Top speed 122mph Price £16,695 Release date 15/05/2010