Among our engineering specializations, that related to the automotive enables us to support our customers at every stage of the development of an extremely complex product such as an automobile. The study of aerodynamics is a very important phase, at the same level of importance as the avionics industry. One of the key parameters we use for the external aerodynamics of a car is the CX coefficient, which is the coefficient of aerodynamic friction.
What is it and how is this coefficient calculated?
CX is a coefficient used to measure the aerodynamic drag that a solid body encounters when passing through a fluid (such as, precisely, that of a vehicle in air). It is calculated with this formula: CX = DA / ½* ρ* V2 *A, then dividing the air resistance by half the density of the air itself, multiplied by the velocity squared for the surface area of the vehicle exposed to the air. Not the simplest formula, but the concept behind it is clear: in principle, the lower the CX, the more easily the car will cleave the air and consequently the lower the fuel consumption and aerodynamic drag. This is a value not to be underestimated when considering the purchase of a car: suffice it to say that a car with a CX of 0.3 needs 13 kW to travel at 100 km/h and 22 kW to reach 130 km/h. A car with CX of 0.4, on the other hand (with an increase of “only” 0.1) needs 3 and 5 kW more to travel at 100 and 130 km/h, respectively. To maintain the higher cruising speed, therefore, there is a need for about two more liters of gasoline per hour. At current rates this is an extra 3.50 to 4 euros: a value that when multiplied by tens and hundreds of times makes it clear how important it is to try to optimize this coefficient, reducing it by even a few cents to improve comfort and performance while decreasing consumption. Suffice it to say that even an open window or an overly bulky antenna can worsen the coefficient. Besides sports cars, which must necessarily have a low CX (usually less than 0.25) in recent years the best cars produced in terms of CX coefficient have been the Toyota Prius (0.25) and the Tesla Model S (0.24). Want more information about our aerodynamic studies or understand how we can support you in designing a new car? Contact us by clicking here.