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For the 2022 season, Formula 1 race cars have aerodynamically smooth wheels, with flat covers attached across the previously open face. Their goal is to reduce the aerodynamic turbulence created by the wheels so that pursuing cars have cleaner air for their wings to produce downforce. This lets the pursuing cars follow more closely, creating increased potential for overtaking.
Mercedes is applying similar technology to the wheels on its new electric SUV, the EQS SUV. The company offers optional 20- and 21-inch wheels that are optimized in the wind tunnel for minimum drag to help increase the car’s driving range and reduce wind noise. Their smooth are called "aeroblades," not the old-fashioned “hub caps.”
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The tire geometry is also optimized with careful attention to the sidewalls and the transition to the tread. We spoke to aerodynamicists Benjamin Arnold, Alexander Gensch and Alexander Wäschle about the importance of wheels for efficiency.
Design News: Why have the wheels become the focus of aerodynamic development?
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Alexander Wäschle: The wheels just get in the way of the wind. On an aircraft, they are therefore simply retracted. Of course, this is not possible with passenger cars; an alternative would be the cover.
But as long as we show the wheels as a design element, we integrate them as best we can under the wheel arches so that as little air as possible hits them directly. But that is not enough. In production vehicles, about one-third of the air resistance is still due to the wheels. It is therefore worthwhile to consistently optimize wheels aerodynamically.
Design News: It sounds like the wheels are only part of a complex system.
Benjamin Arnold: By "wheel" we mean the complete wheel because there is also great aerodynamic potential in the tires. The wheel spoilers, for example, help to optimize the wheel incident flow - these are the downward-pointing lips on the wheel arches in front of the wheels. The wheel spoilers are getting more and more sophisticated 3D geometries. The cooling air from the engine compartment of models with combustion engines that flows into the front wheel well plays just as important a role as the lateral flow over the front bumper and over the doors and side member trim on the rear wheels.
Design News: This must be complicated because there is not just one wheel/tire combination per model series, but many individual variants for the customers.
Alexander Wäschle: Precisely. Wheels not only have to roll, be aerodynamic and quiet, have low rolling resistance, and have plenty of grip. They are also a piece of jewelry and an individualization option for our customers.
Each wheel geometry makes a different contribution to the total air resistance. This means that not just one wheel has to work aerodynamically optimally in its vehicle environment, but quite different wheel designs in different inch sizes. What is more: With each wheel size comes a variety of tires from different manufacturers.
And each one has a different aerodynamic effect. This means that every tire and every wheel is relevant to certification and thus has an influence on consumption and range. As an aerodynamicist, you can really spin your wheels!
Design News: Which details in wheels and tires offer the greatest aerodynamic potential?
Benjamin Arnold: On the tire side, width is the biggest aerodynamic lever. With decreasing tire width, significant coefficient of drag reductions can be achieved. In addition, further improvements can be achieved with optimally designed tire contours.
In the aerodynamic evaluation of the wheels, we pay particular attention to compliance with the "aero ring", the spoke design and a small opening area. The aero ring defines the outer area of the rim and should be a closed ring of adequate width. And many other aerodynamic levers remain our secret, of course.
Design News: How does aerodynamic wheel/tire development work at Mercedes-Benz?
Alexander Wäschle: We have bundled all our knowledge in a cross-series "cross-sectional function wheels/tires" within aerodynamics. This allows us to reliably transfer the latest aero know-how to all model series and to be the central point of contact for all development areas involved. We scientifically develop new aero potentials and optimize and automate the aerodynamic evaluation of wheels and tires.
Design News: How close is the cooperation with other areas such as design?
Alexander Wäschle: In close cooperation with design and the wheel and tire sector, we have achieved a great deal from which the electric vehicles on our new platform benefit. With a lot of creativity, our design colleagues implement the developed aero guidelines without letting the appearance suffer.
[This is] a feat that succeeds with a lot of dialogue in the design phase. With the courage to come up with new constructive ideas, we were able to resolve the conflict of objectives between good aerodynamic performance and the weight of aero wheels together with our specialist department colleagues.
Alexander Gensch: For the experimental investigations, near-production test parts must be created at an early stage. The hardware design envisages the construction and production of carrier wheels made of aluminum, which can accommodate as many different wheel designs as possible in the form of inlays or trim pieces from the 3D printer.
Our own design engineers accompany the entire process, from the construction and the design of the operational stability to the creation of the hardware. The trim pieces are manufactured using various 3D printing processes. Updates in wheel designs, which can be both aerodynamic and design-motivated, can thus be quickly and precisely prepared for assessment on the 1:1 aerodynamic model.
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