Visually, the Cabriolet is recognisable at first glance as a member of the RS 4 family. The rhombus-pattern single-frame grille, the additional air outlets and the new RS 4 wheels lend the open-top four-seater a highly dynamic flavour.

Inside, the seats are the main feature distinguishing the RS 4 Cabriolet from the Avant and saloon. Whereas the other two body versions are equipped with RS bucket seats, the Cabriolet comes with sports seats as standard, though RS bucket seats can be ordered as an option. The most important information units in the Cabriolet are combined beneath a domed cover.

The electro-hydraulic hood can be opened entirely automatically in 21 seconds. The roof can be operated at up to speeds of 30 km/h. This makes it possible to open or close the roof when out and about in town, for instance, or before parking the car. The glass rear window is heated. This guarantees a clear view to the rear in all weather. The acoustic hood, a standard feature of the RS 4 Cabriolet, sets new standards for soft tops. New fabrics of a higher material density and an additional cushioned mat around the C-post keep the noise level inside the car with the hood almost on a par with the saloon.

As with the saloon and Avant, the ride height of the Cabriolet has been lowered by 30 millimetres compared with the A4 Cabriolet. This emphasises the car's sporty appearance.

Even if the Audi Cabriolet's weight has been rigorously trimmed down, in common with all other RS 4 models no corners have been cut with either its equipment or its standards of safety.

The further improved crash strength of the latest A4 Cabriolet generation has likewise benefited the open-top RS 4. The front and side airbags are standard features, as are the rollover bars that extend behind the rear seats in the event of the car overturning.

The 420 bhp V8 revs up to a speed of 8,250 rpm. With its displacement of 4,163 cm3, this outstanding engine breaks through the magic barrier for a production saloon of 100 bhp per litre. The highly compact power unit reaches its peak torque of 430 Nm at 5,500 rpm. At least 90 percent of the maximum torque is available between 2,250 and 7,600 rpm. The result is excellent pulling power at all times, enabling the driver to drive in a relaxed style without frequent gear changes.

Audi's RS 4 saloon employs groundbreaking FSI technology. The petrol direct-injection unit delivers enhanced power output based on more efficient combustion of the fuel/air mixture. The engine is also more responsive. The performance of the RS 4 clearly demonstrates this progress: it reaches the 100 km/h mark in 4.8 seconds (Avant 4.9 seconds, Cabriolet 4.9 seconds), and 200 km/h in 16.6 seconds (16.9 seconds; 17.5 seconds). On all three versions, the speed is governed electronically when the needle reaches 250 km/h.

Audi has deployed the high-revving engine principle for the first time in the RS 4. The advantages of this principle are superior power output at high engine speeds, a smooth power flow and eager responsiveness all across the revs range. Further fortes are the car's outstanding agility and fast-revving response as well as the kind of racing-style engine sound that drivers of such cars simply expect.

As a result of these qualities, the eight-cylinder power unit provides maximum thrust and performance in virtually all driving situations. The constant flow of power from bottom-end speeds all the way up to 8,250 rpm is equally appropriate for a relaxing driving style with minimum gearshifting and for exploits worthy of the racetrack.

The V8 power unit is ultra-compact in its dimensions, fitting snugly into the engine compartment of the RS 4 without necessitating any modifications to the body. The camshaft and ancillaries, with the exception of the alternator, are all driven by a chain for easy maintenance. An all-new development, the eight-cylinder unit powering the RS 4 includes such features as modified pistons and con rods, a new crankshaft together with its bearings, and new cylinder heads.

The car's power-to-weight ratio is also impressive: 3.93 kg per bhp is a figure that only the most thoroughbred sports cars were able to offer just a few years ago. The figure for the Avant is only slightly higher.

Audi translates the engine's power into locomotion in typical style: the latest generation of quattro permanent four-wheel drive, which featured first in the RS 4 saloon and offers a asymmetric/dynamic torque split of 40 (front axle) to 60 (rear axle) in conjunction with the self-locking centre differential, is one of the main reasons why the RS 4 is still able to provide traction when other drive concepts have long since reached their limits. quattro drive is further enhanced by the DRC suspension system (Dynamic Ride Control), which significantly reduces the rolling and pitching movements of the vehicle about its transverse axis and rear axle.

The 30 millimetre lower ride height compared with an Audi A4, the wider track at the front and rear axle and the sporty spring and damper settings help the RS 4 to meet the developers' ambitious handling objectives and place it in the realm of a genuine sports car. The brakes, too, represent new dimensions in their innovation. The 18-inch format provides optimum deceleration.

Floating, perforated, ventilated brake discs measuring 365 millimetres in diameter are fitted at the front, and there are likewise perforated, ventilated brake discs at the rear with a diameter of 324 millimetres. The specifically flow-enhanced brake ventilation incorporating NACA jets on the underbody of the car ensures optimum cooling of the brakes, however high a load they are subjected to.

The latest generation of ESP has been modified specifically to suit the particular properties of this high-performance vehicle. It now intervenes later and for shorter periods. It is also possible to disable the ESP in two stages. In the first stage only the traction control (ASR) function is disabled; the other ESP functions remain fully active. In the second stage the ESP is completely deactivated, including the traction control. All electronic control then ceases.

The servotronic steering has been specially tuned to the requirements of a sports car. With its direct response and short travel, it is outstandingly well suited to the overall character of all RS 4 versions.

Audi has likewise adapted the six-speed gearbox to the handling requirements of a sports car. With its precision navigating through the shift gate and its short travel, it enhances driving pleasure and prompts the driver to change gear more often than the universally free-revving engine actually needs.