Audi A6 Sportback e-tron's astonishing Cd value

THE new Audi A6 Sportback e-tron has set a new aerodynamic record for the brand, becoming the most slippery production model yet with an astonishing coefficient of drag (Cd) number of just 0.21.

The figure means the A6 Sportback e-tron leads the entire Volkswagen Group in terms of aerodynamic efficiency, the A6 Avant e-tron also performing exceptionally well with a Cd value of 0.24 – placing it at the top of its body segment.

According to Audi aerodynamicists Andreas Lauterback and Mattero Ghelfi, and wheel designer Andreas Valencia Pollex, “meticulous attention to detail” helped to bring about the result. Countless hours in the wind tunnel and some 2800 simulations helped fine tune the A6 Sportback e-tron toward its impressive number.

“From the very start of the project, we placed a high value on efficiency and range and pursued very ambitious goals, regarding the A6 e-tron,” explained Mr Lauterback.

“To be honest, in the beginning, we weren’t sure if we would be able to achieve the values we were aiming for. Getting to that last thousandth of a Cd value is the hardest part, but in the end, we exceeded our goals.”

Well-designed proportions, a slim greenhouse and sloping roofline contributed to the overall score, the collaboration between designers and aerodynamicists adding elements such as flush-fitting air curtains at the front of the vehicle, a smooth underfloor, rear diffuser, and unique aero bezels at the rear wheel arches.

The vehicle’s wheels – a major contributor to aerodynamic turbulence, and therefore drag – also received particular attention, with all three designs (one 19-inch and two 20-inch options) becoming what designer Andreas Valencia Pollex describes as “intelligent aero wheels”.

“Formerly, wheels basically only had to meet stability requirements,” he said.

“Today, we develop and design intelligent aero wheels that are as efficient as possible because the wheels, and even the tyres, have a major impact on the range of an electric car.

“To achieve perfect aerodynamics, the rims had to be somewhat flat so that the air that hits the front of the car is directed sideways around the body without much turbulence. We want the wind to flow along a wall rather than a collection of geometric shapes.”

Audi – or more accurately Auto Union – has a long and fabled history in aerodynamics.

In 1938, Auto Union driver Bernd Rosemeyer set a public road class speed record of 432km/h in a streamlined model developed to cheat air resistance. The 1967 NSU Ro 80 had an aerodynamic, wedge-shaped body with a Cd value of 0.35, while the third generation Audi 100 (C3) built in 1982 had a Cd value of just 0.30.

Right on its heels, the third-generation Audi 80 (B3) continued this success story with a drag value of 0.29.