Torque Shop: EVs and aerodynamism

Electric cars tend to be aerodynamic, like the Porsche Taycan 4S Cross Turismo. PHOTO: ST FILE

I notice that most electric cars look very sleek and quite different from the typical styling of petrol cars people are used to. Is this because the manufacturers want electric vehicles (EVs) to look futuristic or are there other reasons?

There can be no denying that EV manufacturers strive to make their cars look as high-tech as possible. However, this is only a small reason.

The No. 1 design objective is to optimise energy efficiency. To this end, aerodynamics plays a major role in the design of EVs.

Drag or resistance from air acting on a moving car naturally causes an increase in the consumption of energy – whether it is powered by fuel or electricity.

The force of air against the direction of motion rises rapidly as speed increases. For example, the theoretical resistance on a car travelling at 120kmh is four times higher than when it is cruising at 60kmh.

It is the same scenario on any vehicle, but because the EV’s powertrain is far more efficient than that of a combustion-engined vehicle, and since EVs start with a huge weight disadvantage because of hefty batteries, aerodynamics becomes a greater contributing factor in overall efficiency.

At cruising speeds, drag alone can easily account for more than 50 per cent of an EV’s energy consumption.

Fortunately, the EV is an inherently ideal design for the aerodynamist. Its underbody, which is bereft of transmission or exhaust pipes, can be fully closed and flat. As the electric motor and other powertrain components do not require air-cooling, there is no need to provide drag-inducing grilles or intake apertures.

Hence, many of the EVs today have very short and sleek bonnets, covered or fake grilles, swooping rooflines and smooth wheel designs.

Although more challenging in terms of aerodynamic designs, some keep to a more traditional look. One example is the new BMW i7, which can still achieve a drag coefficient (Cd) of 0.24 – a figure that compares favourably with the sleeker Porsche Taycan’s 0.22.

A vehicle’s frontal area is another important factor that influences drag. The narrower and lower a car is, the less air resistance it has. This is why even if a sport utility vehicle has a low Cd of, say, 0.25 or less, the net effect of air resistance is significantly higher than on a sedan with an equivalent Cd value.

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