AUDI is expecting big things from its smallest four-seater convertible, the A3 Cabriolet.

On sale now from $49,900 and available in two TFSI turbocharged direct-injection four-cylinder petrol guises, the German-built two-door ragtop is gunning for the similarly priced BMW 120i Convertible.

It is also pitched against rivals as disparate as the Mini Cabrio, Volkswagen Eos and Saab 9-3 Convertible, although Audi claims the in-house VW appeals to a different type of customer.

The A3 Cabrio is based on the second-generation Audi A3 unveiled in 2003 – itself derived from the current VW Golf V platform – so shares many components with a host of other VW group vehicles such as the Skoda Octavia and Audi TT MkII.

Both A3 Cabrios are front-wheel drive for now, and use the basic MacPherson strut front and four-link independent rear suspension that forms the backbone of the Golf V understructure.

But it is what’s on top of the car that is the Cabrio’s party piece.

Like BMW’s baby ragtop, Audi has elected to eject the fashionable folding hard-top for more traditional folding fabric sheathing a movable metal frame, in the interests of lightness, maximised boot space and overall simplicity.

It employs a new ‘Z-fold’ design, whereby the soft top concertinas into a compact space. Uniquely, when folded down, the front of the roof (header) a made of a hard board that rests flush with the car body and is hydraulically locked into place to form a sturdy cover, in lieu of a tonneau or box cover.

When folded down, the soft top is positioned within a steel metal compartment featuring a slanted floor, thus minimising boot space intrusion.

Two roof-powering mechanisms are being offered.

The basic system is a semi-automatic that requires the car’s occupants to latch and unlatch it via a central handle located on the windscreen header rail once the motors have whirred it into position.

Alternatively, as part of a $1300 ‘Acoustic Top’ option that also includes three (instead of two) layers for better soundproofing and thermal insulation, there is a full-automatic roof with an electric ‘latching’ motor.

Thanks to a high-pressure pump and two hydraulic cylinders, Audi says the roof opens in a class-leading nine seconds and closes in 11, while the Acoustic Top can be activated at speeds of up to 30km/h or remotely via the key.

For $650, there is a simple wind deflector that sits over the rear seats, rendering them useless for people with heads, and folds neatly into the boot when not needed. The windscreen is at the same angle as that of the regular A3, creating a more ‘open’ feeling (and letting in more air turbulence at speed) than most folding hard-top convertibles, according to Audi.

Audi’s tests in Germany show that, at 140km/h, an A3 Cabrio with the Acoustic Top erected is just one decibel louder than the equivalent hatchback, at 71 dB.

All four windows can be lowered via a single button, and the rear one is a heated glass item.

Interestingly, at 218mm long, the A3 Cabrio’s roof length exceeds the larger A4 Cabriolet’s by 19mm. It is also available in three colours – black, blue and red.

Audi likes to boast about class-leading luggage space, aided by a standard split-fold rear seat, which provides a capacity of between 260 and 674 litres whether the soft-top hood is open or closed.

Meanwhile, over at the front of the car, lives a turbocharged twin-cam 16-valve variable valve timing-equipped direct-injection four-cylinder petrol engine in either 1.8 or 2.0-litre capacities.

The former is the lightweight 1798cc unit that debuted in other A3 (as well as Skoda Octavia) variants last year, delivering 118kW of power between 5000 and 6200rpm and 250Nm of torque from 1500 to 4200rpm.

Audi’s famous DSG six-speed twin-clutch transmission (now known as S-Tronic) is the only gearbox on offer with this engine, but the larger, 1984cc 2.0-litre unit – known from a wide variety of VW Group cars but most famously the current Golf GTI – is available with both S-Tronic and a six-speed manual shifter. Its power and torque outputs are 147kW between 5100 to 6000rpm and 280Nm between 1800 and 5000rpm respectively.

Both engines return 7.6L/100km, while the 1.8’s 180 grams per kilometre of carbon dioxide emissions is just 1g/km less than the 2.0 S Tronic and 2g/km better than the 2.0 manual.

If you’re game for a 0-100km/h sprint, the smaller unit trails the 2.0’s claimed 7.3-second dash by 0.7 seconds, while the 218km/h top speed is 13km/h shy of its big brother.

The engines must haul around a car that is up to (at least) 100kg heavier than its hatchback counterpart despite sitting on the same 2578mm wheelbase, due to a high amount of re-engineering necessary to maintain strength, rigidity and safety levels.

To this end, 54 percent of the Cabrio’s body is composed of high-strength and ultra-high strength steels, integrated as reinforcing in the A-pillars, side sills, floor, doors and rear wall.

Audi has also braced the sub-floor and front and rear-ends, while a box-shaped steel structure separates the passenger and luggage compartments. High-strength steel tubing is bolted into this structure to form rollover hoops for greater occupant protection, aided by the beefed-up pillars.

Located in the backs of the front seats are sensors that respond to a rapid change in air pressure, activating the head-thorax side airbags.

These, along with dual front and side airbags, electronic traction/stability control, daytime running lights and an anti-lock braking system (ABS) with electronic brake-force distribution (EBD), electronic differential lock (EDL) and Brake Assist, form part of the standard safety equipment levels in the A3 Cabrio.

Steering is via an electro-mechanical speed-dependent rack-and-pinion unit, while brake discs are either 15-inch (1.8) or 16-inch (2.0) in diameter, with the fronts being ventilated.

The 1.8 TFSI is available in Attraction-only equipment grade for now, while the 2.0 TFSI opens with the better-equipped Ambition specification, which adds items such as 15mm-lowered ‘sports’ suspension, 17-inch 225/45 alloy wheels and tyres instead of the former’s 16-inch 205/55 pairing, front foglights, more salubrious cabin trimmings, the aforementioned wind deflector, ‘sports’ front seats, higher-end audio, a more comprehensive trip computer.

The 2.0 TFSI is also available with a ‘Comfort Package’ consisting of leather trim, rear parking radar and a mobile phone preparation with Bluetooth.

Options include high-intensity discharge (HID) headlights with adaptive headlight and cornering light technology, plus LED daytime driving lights that define the latest Audis, as well as a removable ski-bag, anti-theft alarm and satellite-navigation, among other items.

More engine variants are expected to top and tail the A3 Cabrio range – from a 1.6-litre or even the 1.4-litre TSI turbocharged and supercharged four-cylinder petrol units, to the 2.0-litre turbo-diesel.

Audi expects to sell around 300 A3 Cabrios this year, with about half already accounted for.