This Article Can Be Summed Up As Follows
The role of aero parts is to reduce drag and increase downforce.
Their effects vary greatly depending on speed range and vehicle shape.
If they are installed without understanding how they work, they can even be counterproductive.
Aero Parts Are Not Just for Looks
When modifying your own car, what do you place the greatest importance on? If you are focused on performance, you will probably think first about mechanical upgrades, but how should aero parts be understood? By fitting aerodynamic parts, can you really feel improvements in driving performance that a stock car does not offer, such as more stability in high-speed cornering or sharper handling?
Looking at the market, there is an enormous variety of aero parts available. Even a quick count turns up front bumper spoilers, lip spoilers, rear bumper spoilers, rear diffusers, rear wings, rear spoilers, roof spoilers, and, beyond parts that correspond to sections of the body itself, small items such as vortex generators that are attached directly to the body surface. The range and number of choices are extensive.
The key point is how you think about these parts before fitting them. Whenever the subject of aerodynamics comes up, it is usually explained that improving aerodynamic performance can broadly be divided into two elements. One is reducing air resistance, and the other is increasing downforce.
The factors that reduce air resistance are a reduction in projected area, mainly frontal projected area, and a reduction in the drag coefficient, or Cd value. Stability in a moving vehicle is achieved through an increase in downward lift, which is to say downforce.
Of these two, reducing air resistance literally means reducing the aerodynamic drag acting on the body while the car is in motion. That is determined by the size of the body area receiving the air and by how smoothly air flows over the body surface. On a production vehicle with a body shape that is already fixed, this is an area that is difficult to improve after the fact.
For example, a front bumper spoiler, whether it is integrated into the bumper or added later, increases the area that receives the airflow when it is installed. Even so, there are cases in which the Cd value improves because the airflow itself becomes smoother. A lip spoiler, on the other hand, increases resistance because it catches more air, but by changing the airflow and straightening it, it also works to increase front-end downforce.
Understanding the Role of Each Part Is Important
In that sense, the parts that probably attract the most attention are the rear wing and the rear spoiler. Their original purpose is to increase downforce at the rear of the vehicle and stabilize the car’s attitude while cornering, although it should also be added that they deliver a strong dress-up effect.
Front spoilers and rear spoilers or wings work to stabilize the vehicle’s contact with the road by increasing downforce at the front and rear, but it is difficult to say clearly how much of that effect can be felt at the legal speed limit of 120 km/h. This is another point that always comes up in discussions of aerodynamics: air resistance is proportional to the square of speed. Even if the effect feels slight at 100 km/h, when the speed doubles to 200 km/h the resistance value, and it is fair to think of downforce in the same way, becomes four times greater, making the effect much easier to feel.
In the same way, a vortex generator, which changes the airflow, can in some cases be considered one of the aero parts capable of producing a considerable effect. It is a small part, and if its function is explained as creating turbulence, that may sound suspicious at first. But if it is installed at the rear of the body, for example at the trailing edge of the roof, and turbulence is then generated behind it, that may seem negative at a glance. In reality, however, that turbulence suppresses the formation of separation vortices, which create large amounts of drag, so from an aerodynamic standpoint it works strongly in a positive direction.
There is one important caution with vortex generators: there are specific rules for where they should be mounted and how many should be used, and if those rules are not followed, they will not deliver the intended performance.
Using aero parts to improve performance is not wrong in itself, but the degree of improvement they provide varies enormously. That is because major differences arise depending on the vehicle they are fitted to, meaning its body shape, and on the shape of the part itself. The way the effect appears also changes according to the speed range in which the vehicle is driven. As a basic rule, you should understand what the part you are installing is meant to do, and then avoid fitting other parts that may cancel out that effect.
