The faster we drive the more the air starts to thwart. Logical. However, doubling the speed does not mean that the air resistance will then be twice as great. No, the air resistance increases exponentially. And the ability to split the air increases by another factor, this is speed to the third power. Manufacturers are therefore very keen to keep the other variables as low as possible in order to limit consumption and CO2 emissions. That sounds complicated, but is it?
Air resistance is the most important of all driving resistances. That is why the car manufacturers do their best to let the air flow past the car with as little delay as possible. The formula for calculating the air resistance is the product of four variables: the air density, the frontal area of the car, the air resistance coefficient (the Cw value) and the speed squared. Power is power times speed. The power required to overcome the air resistance has been presented in a very simple way, so it is nothing more than multiplying the product of the air resistance formula once more with the speed. This means that the influence of speed on this part of the required power is in the third power. And when you consider that the requested power is directly related to fuel or electricity consumption, you see that the influence of speed on consumption is significant.
As a constructor you have no influence on the airtightness, nor the speed that the motorist will drive with the car. What you can do about as a manufacturer is the frontal area of the car and the Cw value. And that happens to a large extent. Although that sounds easier than it is, a car is one big compromise. For example, the frontal area is largely influenced by the height and width of a car (coincidentally also the dimensions that play an important role in determining the interior space) and with the popularity of SUVs, the height increases even more. Oh, and then we also want ever wider tires … The increase in the frontal area can then only be compensated by lowering the coefficient of drag as much as possible. This not only means the body drawn as smoothly as possible, but also the flatest possible bottom. And what about the air that enters the engine compartment through the grille? To suppress the negative consequences of the latter as much as possible, we often see slats behind the grille that can be closed and, for example, we are also working on aerodynamics under the hood.