Tech Talk: Why electric car aerodynamics are so important

Has it really been 40 years since the launch of the revolutionary third-generation Audi 100, with its drag coefficient of just 0.30? It was big business at the time and reflected the change in mentality following the fuel crisis of the 1970s from which the world had not emerged for a long time.

The subtle 100 certainly looked slick compared to others from that era, but it was far from exotic and perhaps that’s what made its revolutionary aerodynamics all the more interesting.

It’s no secret how important this moment has become in the automotive timeline, but today, given the massive improvements in knowledge and technology available, what can we expect to the future ? How much drag can continue to be reduced? How will it affect the appearance of cars? What impact is electrification having and will it have in the future?

The parasitic drag caused by the air gripping the surface of the car and trying to slow it down is fearsomely powerful, increasing as the square of the speed. Simply put, that means doubling the speed requires four times the power to overcome the drag. Think, for a moment, of the efforts to massage powertrain design to extract more power, and all of a sudden the fuss around aero makes more sense.

Because electric powertrains are so much more efficient than combustion engines, the contribution of aerodynamics to a car’s overall efficiency becomes even more alarming.

According to Thomas Wiegand, head of aerodynamics R&D at Porsche, drag accounts for 30-40% of electric car losses on the WLTP driving cycle, rising to 50% in the real world. In comparison, drag losses are only 10% of the overall losses of combustion engine cars.

The good news is that EVs have several advantages over ICE cars in the aero department. The first is that power units generate much less heat to remove, which means little or no airflow is needed through a radiator and engine bay.

Another is that a lack of exhaust plumbing—and transmission components in some cases—means the undersides are easier to get absolutely smooth. The increasing use of active aerodynamic devices, such as shutters, means that only the necessary amount of air is allowed to flow over brake discs and radiators.

The Porsche Taycan and Mercedes EQS achieve drag coefficients of 0.22 and 0.20 respectively, and the Mercedes EQXX concept drops them to an almost unbelievable 0.17.

Mercedes aerodynamics engineer Stefan Kröber explains that the figures translate to an energy consumption of 15 kWh per 100 km for the EQS, but this drops considerably to 10 kWh for the EQXX. Porsche expects cars to change shape while moving in the future, possibly using shape-memory materials.

Research is also underway at the University of Stuttgart, where loudspeakers are used to introduce outer surface vibrations to influence airflow separation behavior and further reduce drag.

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