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Aero is either a simple subject about body styling, or an incredibly complex scientific affair about using airflow to make your car perform to its maximum abilities.
As it’s quite a big subject, we’ve decided to split this into this two article. In both of these we’ll aim to cover both aspects without confusing the hell out everyone.
Here in part one, we are going to look at the science behind aero, and some of the most popular styles you’ll see on both the street and track.
In the next article we will explain all those special mods you can make to your motor, what they’re there for, and the key things to consider when planning your ultimate aero ride. Anyway, let’s crack on…
WHAT IS AERODYNAMICS?
Until around ten years ago, a bodykit was just a bodykit in the modified car scene – you simply fitted it to your car because it looked cool, and that was that. These days however, thanks to the popularity of things such as Time Attack, drifting, and track days – not to mention the Japanese import revolution – things are very different, and aero is now the common term for body mods that create (or at least look like they create), an aerodynamic performance advantage.
Until around ten years ago, a bodykit was just a bodykit in the modified car scene – you simply fitted it to your car because it looked cool, and that was that. These days however, thanks to the popularity of things such as Time Attack, drifting, and track days – not to mention the Japanese import revolution – things are very different, and aero is now the common term for body mods that create (or at least look like they create), an aerodynamic performance advantage.
While the vast majority of people fit aero to road cars purely as it looks cool, when done correctly, it really does have an effect when a car is pushed to the limits. Straight line speed, cornering speed, braking, cooling, and engine efficiency can all be improved by clever aero design.
While it’s common to associate the word aerodynamics with how easily something will fly through the air (a dart is more aerodynamic than a brick wall for example) aerodynamics, or aero, involves far more than that. It covers every aspect of airflow associated with a car, and can have a massive effect on performance, stability, and safety. Not only is it about how the car will cut through the air when screaming down the tarmac, but it’s about drag, downforce, lift, flow in, and out of various holes on the car – even how air is channelled over the body by certain aero parts.
Providing you’re not drifting (or about to have a crash) the front of your car will always be facing the direction of travel. So the air that it hits has to go somewhere, either over it, under it, around the sides of it, or through holes in the front end of the car. And this is what aerodynamics is all about – it’s the science of how much of this air goes where – from this first point on the front bumper until the very rear of the car.
The main thing to remember, before we get started, is that the effects of aerodynamics increase with speed. So at what speed it becomes effective, really depends on how extreme the aero is. Some vehicles, such as rally cars, have aero that can be effective at a little over 30mph, but this setup won’t be very good for high speed use, as it would cause huge drag above 100mph. Most circuit race car aero, on the other hand, has very little effect under around 60mph or more – but won’t cause anywhere near as much drag at higher speed. This enables the cars to hit the high speeds needed to be competitive. So at the end of the day, it’s a balancing act, dependant on what you need from a car.
WHAT IS AERODYNAMIC DRAG?Aerodynamic drag refers to how easily your car cuts through the air. The less drag you have (if all else is equal) the faster your car should accelerate, the better the fuel economy should be, and providing you have the gearing for it, the higher potential top speed you will have too. About 1/3 of the air that hits the front of your car tends to go underneath, including around the wheels, exhaust, transmission, and so on. About 1/3 goes around the bodywork, and the final third tends to go through the openings in the grille and bumper and into the engine bay. Because of this, cars that are intended to have high top speeds, such as supercars tend to have very aerodynamic body shapes and smooth undersides to reduce drag. Even ‘eco’ cars such as certain hybrids and VW Bluemotions have aero parts like very small front grille and bumper openings to reduce drag with the aim of improving fuel economy.
WHAT IS AERODYNAMIC LIFT?
Lift is exactly what it sounds like – airflow that tries to lift the car from the ground – really not what you want for performance. Lift is affected (mostly) by the amount of air travelling underneath the car, and how quickly it can escape. The more air under the car (and longer it is under there) the worse lift tends to be. Airflow above the car affects lift too, as while long smooth bodywork has less drag, it also tends to increase lift too. Lift reduces tyre grip, and, in extreme instances, can send the car almost totally out of control. Race cars have even been known to lift their front wheels and even flip over, due to extreme levels of lift. Search YouTube for “Le Mans flip” to see what we mean!
Lift is exactly what it sounds like – airflow that tries to lift the car from the ground – really not what you want for performance. Lift is affected (mostly) by the amount of air travelling underneath the car, and how quickly it can escape. The more air under the car (and longer it is under there) the worse lift tends to be. Airflow above the car affects lift too, as while long smooth bodywork has less drag, it also tends to increase lift too. Lift reduces tyre grip, and, in extreme instances, can send the car almost totally out of control. Race cars have even been known to lift their front wheels and even flip over, due to extreme levels of lift. Search YouTube for “Le Mans flip” to see what we mean!
WHAT IS AERODYNAMIC DOWNFORCE?Downforce is exactly the opposite of lift. It is air pressure – literally pushing the car, and therefore the tyres – into the tarmac. If the car is pushed towards the surface by the air, straight line and cornering grip is increased, and the potential improvements from this are absolutely incredible – as shown by Formula 1 and Le Mans cars. Unfortunately, the majority of things that increase downforce also increase drag, so it’s a real balancing act to create the required amount of downforce, without so much drag that the car’s top speed is too limited.
WHAT IS COOLING AIRFLOW?
This is airflow, which, while not directly related to the car’s handling, almost always creates drag and lift at the same time. Cooling airflow does exactly what it says it does, it’s the air needed to hit your radiators, oil coolers, and intercoolers, to prevent your engine from overheating and to create maximum power. While every car’s aerodynamics would be better if there was no need for cooling holes and ducts, they are unfortunately vital for performance.
This is airflow, which, while not directly related to the car’s handling, almost always creates drag and lift at the same time. Cooling airflow does exactly what it says it does, it’s the air needed to hit your radiators, oil coolers, and intercoolers, to prevent your engine from overheating and to create maximum power. While every car’s aerodynamics would be better if there was no need for cooling holes and ducts, they are unfortunately vital for performance.
WHAT IS STABILITY AIRFLOW? Unlike other aero changes, which tend to have side-effects, aero that affects straight line stability tends to have very little difference in drag, lift, or downforce. This is the least common aero mod both on road and race cars, but it does exist. It’s used to improve straight line stability at high speed, and reduce the chances of lift if a car does go sideways – some race cars have been known to lift up and flip over if they go sideways at high speed!
BERG CUPThis style of aero is based around European hillclimb racers, often called Berg Cup-style after the German hillclimb event of the same name. Berg Cup cars tend to be ’70s, ’80s, and ’90s hot hatches and coupes, They had massive bolt-on wheel arches to house the mega wide wheels and t
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