The aerodynamic coefficient of a car

In the mid-sixties of the last century, the automotive industry in Europe and the United States was blooming like a sakura tree in spring. By the way, Japan also had a certain increase in production in the automotive industry. Car recycling service is popular nowadays:

New models entered the market, new brands were created, and automobile concerns were born that included more than one car brand. Accordingly, as the number of produced cars increased, so did interest in them. Even now you can see the boys who are interested in looking at any unusual car.

 After examining the body and making little jokes about the owner of this car, it was imperative to look at the speedometer of the car, for that was the only way to determine whether the car was fast or not.

To a great disappointment, the youth of those times, and probably every other youth who thought that the maximum number on the speedometer of the car was a real reflection of its abilities, learned with age that far from this detail in the car could fully speak about the speed capabilities of the vehicle.

 In addition, history knows examples when manufacturers deliberately underestimated the maximum value of the speedometer, counting that hotheads will not try to squeeze the maximum capabilities of the available car. After all, high speed, especially in the company of alcohol and provoking passengers, not seldom led to tragic consequences. For this reason, people lost both their health and their lives.

 Over the years, when the young people who looked into the speedometer got the necessary knowledge, the understanding came that the main indicator of speed is not the speed sensor. A lot in this respect depends on the body. More precisely, from its structure.

If you look at sports cars, which are in millionaires’ garages, you can see there, as a rule, mostly streamlined bodies. With a lowered front and a slightly raised rear. Plus, on the trunk, as a rule, there is also a spoiler.

 Sports cars are built that way for a reason. Such shapes of the car help to reduce the frontal air resistance. In other words – aerodynamic. The faster the car is moving, the faster the aerodynamic drag increases.

For convenience, such a phenomenon is called the coefficient Cx. This value can only be calculated experimentally. Therefore, car manufacturers are forced to equip their laboratories with a wind tunnel.

 This tube is quite an expensive pleasure, but it allows you to study all the properties of the body in the process of research. Thanks to these experiments, it is possible to finalize the design of the body at an early stage, and to put into production in the future already qualitatively elaborated car.

 The minimum value of the coefficient Cx known at this time is 0.05. True, it is not a car, but a drop. Most modern cars have an average value of 0.3-0.35 coefficient. The lower this figure, the more perfect the car body is considered.

In addition to what has already been said, this coefficient is also important in terms of reducing fuel consumption. The lower it is, the easier it is for the car to move without encountering strong resistance. With significant resistance, it would be necessary to increase the volume of the engine, and this is an additional mass of the car, and to move this weight from place and move in space, would have to spend quite a lot of fuel. 

Another weighty point in a car’s aerodynamics is downforce. The essence of this effect is that when the car moves, it sort of cuts through the air like a knife cuts through butter. And just as the knife has oil on both sides, so the air flow, separating at the front of the car, passes from above and below. The flow passing overhead will push the car to the ground, giving the wheels better traction. The flow passing underneath the car will try to lift the car. 

Precisely because at a certain speed the car may begin to lift and therefore there will be a deterioration in wheel-to-wheel contact, all race cars, and now ordinary civilian cars, in an attempt to mimic a sports car, have a spoiler. Due to this body part, the car is better pressed to the ground and does not lose its qualities in terms of handling.

 There is a lot of controversy regarding spoilers among owners of civilian cars, which are not designed for racing. Someone says it is just a decorative ornament for the car and it does not give any advantages on the road. Others, as a rule the owners of spoilers declare that with it the difference in motion is quite noticeable.

 It is strange but in this case both parties will be right. True, only partially. A spoiler really increases downforce, but when driving from 120 km/h. And for a city drive, if you don’t develop such speed, you can do without it.

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