Rolling stock

At first glance it is one of the few constants in automotive design. Call them rolling stock, rims or just wheels, they may have changed in size, width and spoke design and materials over the years, but the basic circular shape has remained.

But with the arrival of electric vehicles and the greater emphasis on aerodynamics as a contributing factor in vehicle range, even the wheel needs to be optimised – or reinvented.

Andreas Valencia Pollex is a wheel designer at Audi whose task has been to reinvent the wheel for e-mobility. No small brief to be sure, but one that he and his team have taken to with relish.

Audi Magazine: Electromobility has brought special demands in terms of design and aerodynamics. On the one hand, it allows new approaches to design, while on the other, wheels are getting bigger because they have to carry more weight. But, large wheels present challenges in terms of aerodynamics. As an Audi designer, how do you manage this balancing act?

First and foremost, a wheel is a safety-relevant component. All the forces generated by a car are transferred to the road via the wheel/tyre configuration. Yet unlike a chassis component, the wheel is visible to the outside. We wheel designers are thus creating something that has to meet the technical requirements while at the same time satisfying design aspects. The energy balance of an electric vehicle is crucial so the focus has shifted accordingly. Previously, wheels really only had to deliver on strength requirements.

What is it that makes an ideal aero wheel?

The perfect interaction of vehicle body, tyre and alloy wheel – and the position of the wheel in the wheel housing. To ensure perfect aerodynamics, we need to achieve a certain flatness so that the air hitting the front of the car is diverted around the vehicle body without causing strong turbulence along the sides. The paradox here is that creating flatness on a wheel always involves quite a lot of work. A closed surface means using more material and, in the case of aluminium, that results in a certain weight increase. That’s why we have used plastic to create the closed surfaces on the wheels for the Audi e-tron GT quattro. This keeps the wheel weight down.

Why don’t you just put a flat cover on the wheel?

Our customers who buy a beautiful premium vehicle expect absolute functionality but also uncompromising aesthetics. On wheels, extreme flatness is not yet accepted as being beautiful. Our aim is to develop an aesthetic that conveys the innovation of electromobility while meeting our customers’ expectations. From a purely technical viewpoint, it’s not possible to use entirely closed wheels. If the brakes are deprived of air, the brake fluid would eventually boil and cause a safety issue. A certain amount of ventilation is essential. In aerodynamic terms, we have nevertheless succeeded in balancing the geometry of this wheel for the Audi e-tron GT quattro so that it makes no difference whether the air sweeps across all the angles and openings or whether the surface is entirely closed.

Don’t the openings cause an air vortex?

No. Together with our aerodynamicists, we have found the exact sweet spot that lets air through to the brake while steering the airflow as if the surface were closed. At the speed at which it flows through the wheel, the air can only react as dictated by physics. In aerodynamic terms, the Audi e-tron GT quattro wheel represents the absolute state of the art.

Is the frame of the aero wheel still made from aluminium? Is plastic only used for the cover components?

That’s right. If you look at the wheel from the inside, you’ll see five straight spokes which ensure maximum stability. Aluminium remains an essential material for wheels. Its technical properties, such as plasticity and strength, don’t change. Aluminium is also resistant to the tremendous heat generated by the brake on the inside of the wheel. Having said that, a classically designed five-spoke wheel would be virtually ineffective aerodynamically. And creating a flat aluminium part would have made the wheel too heavy. During the development process, we found we could use plastic inserts to close the surface. This makes the wheel particularly light. The properties of the various plastics are very interesting in terms of identifying which plastic will withstand brake heat at which point on the wheel.

How did you approach designing this wheel?

The top priority was to achieve a progressive design. We started by sketching a wheel with a certain flatness to prevent major errors creeping in right from the outset. But the wheel’s final design was the result of perfect collaboration with colleagues in manufacturing, production and aerodynamics. One example is this key two-part plastic component that creates flatness and looks like a wing. The two parts are clipped together and then screwed to the wheel at a different geometry. We really wanted it to be a bicolour component. Initially, the light-coloured part was made from aluminium but that turned out to be too heavy. So we had to use a plastic, which we precision-coated. We weren’t trying to recreate high-sheen aluminium. The intricate interplay of all disciplines is the only way to achieve the precision needed to create this component with the progressive design and durable construction that can withstand all driving conditions in any weather.

Where is the Audi DNA in this wheel design?

Basically, the Audi DNA can be found in every part of the wheel. Each and every detail radiates design quality – the clarity, the precise choice of angles, the balance of the lines that come together in an arc. If you have an eye for design, you’ll appreciate this quality. And if you don’t know a whole lot about design, you’ll still find it soothing on the eye because everything about the wheel is appealing. That’s Audi DNA. That’s design quality. At the time we designed the wheel, the goal was to make the Audi e-tron GT quattro look as progressive, electric, modern and sharp as possible. You’ll find all that in this wheel.