Given the current controversy over the design of the Brawn GP, Toyota and Williams diffusers Racecar Engineering decided it was time to return to the basics of racecar aerodynamics. This will allow us to better understand exactly why their designs are more effective. What this actually means in real world terms is that the shaped piece of bdywork at the rear of say an F1 cardraws the air out from under the car.

This literally sucks the car to onto the track creating much higher grip levels than would otherwise be available simply through the tyres and suspension setup.

This is known as aerodynamic grip. The theory To understand why this works one first has to have a grasp of the basic principles of lift and down force. The illustration below shows a simple downforce generating wing profile. The air passing under the wing has further to travel than the air passing over the top surface. This causes the air under the wing to accelerate, resulting in a drop in air pressure, this creates a difference in pressure between the upper and lower surfaces.

This difference essentially means the wing is pushed down by the higer pressure above, generating what is known as downforce. An extreme application of this theory can be seen on the Chaparral 2J car above. A pair of fans on the rear of the car sucked the air from under the floor, pulling it onto the road, rather like a reversed hovercraft.

With this in mind, the role of the diffuser on a racing car is to speed the airflow up underneath the car, reducing its pressure, creating a greater difference in pressure between the upper and lower surfaces of the car. This means more downforce and aerodyamic grip, allowing the car to corner faster. Now that we understand the basics of downforce generation we can look at the more detailed operation of a diffuser, and why they have their distinctive form.

The diffuser increases in volume along its length, creating a void that has to be filled by the air passing under the body. This venturi effect means that the flow is accelerated through the throat of the diffuser, creating the desired low pressure, then gradually returned to the same velocity at which it joined the wake See Fig 1. The angle or slope of the diffuser is also important, the diffuser must have a gradual change of angle to prevent flow separation from its roof and sides.

McBeath,Competition Car Downforce. Fig 2 Fig 2 shows the pressure coefficient of a generic diffuser design, with blue reperesenting lowest pressure areas and red highest pressure.The same principles which allow aircraft to fly are similar in racecar aerodynamics, but the main focus is to produce downforce instead of lift know as negative lift. The ideal set up is normally to get the maximum amount of downforce, for the smallest amount of drag generated.

Gear ratios, track configurations and regulations all have an effect on the overall package, which must be viewed as a whole. Another important factor is aerodynamic balance, which will have an effect on the understeer versus oversteer handling characteristics of the car- especially at speed as most aerodynamic devices start to work exponentially with speed.

Below are some general guidelines, of what downforce set ups will be the most advantage for different tracks layouts:. Bear in mind that we are speaking about a general rule of thumb, with a well balanced and correctly set-up racing car. Most race cars aerodynamics will have a selection of different settings for the various aerodynamic aids front wing, rear wing, and diffuser for example to get the optimum set up for the highest lap times, depending on the requirements.

How does downforce help a NASCAR race car?

While this might not always be the case with normal productions cars, some vehicles might be set up to produce real down force Ford Escort Cosworth for example while others are more geared towards fuel efficiency and visual appealing looks, with the intention to stop lift and reduce flow separation and not to create downforce. The 3 main areas of the racing car downforce generating devices, which can be developed are the overall body is important but is normally predetermined at point of initial design :.

One of the main physical forces involved in down force generation is called the Bernoulli Effect, fundamentally meaning that if a fluid gas or liquid flows around an object at different speeds. The slower moving fluid will exert more pressure than the faster moving fluid on an object. The object will then be forced toward the faster moving fluid, creating negative or positive lift.

downforce on race cars

With racecar aerodynamics we need to force more high speed low pressure air to go under the aerodynamic devices creating negative lift downforce. Downforce is produced at the square of velocity travelled- we have to bear in mind that every action has a reaction Newtons Third Lawinterestingly enough, drag is also produced at the square of velocity travelled. More downforce results in higher grip levels for the tyres and more traction, especially going through the corners, braking and accelerating all enhanced.

A F1 car can produce enough downforce to drive upside down three times the car's weight in certain configurations. It can produce more downforce than the weight of the racecar and this force is the square of the object velocity double the speed and you get quadruple downforce and drag levels. While this downforce generation is desired if you going from Mph straight into a sweeping corner or hairpin. A dragster or race car focused on top speed will be more interested in a low drag set up.

downforce on race cars

This extra drag will hinder top speed and more engine power will be required to propel the car forward. It is a balancing act for top speed and downforce levels, hence the reason most competitive race cars will have adjustable aerodynamic aids to suit the best downforce levels for a given race track. A Indy car for example would probably be generally set up to have a greater top speed then a F1 car as a comparison, as the F1 car will require greater levels of grip and downforce for the corners, especially with its rapid directional changes to reduce lap times.

Otherwise high downforce levels will compromise the rest of the course, for high top speed on the straights. It all comes down to different set ups for different race courses. Like a lot of components on race cars, it is possible to adjust the aerodynamic levels of the required downforce to yield greater top speeds depending on the circuit.

From the F1 season, it allowed for less downforce generation to aid overtaking on the straights, by changing the rear wings angle of attack wing profile. Here is an interesting fact: the average atmospheric pressure at sea level is So these small little adjustments can yield impressive results. Racing cars and aerodynamics have come a long way in terms of development since basic ground effects where first applied to cars.

In the early days ofcars like the Lotus 49 and Lotus 79 for example, initially had huge rear wings, which were mounted on the rear suspension mounts. A little later they even introduced cable operated wings to reduce the angle of attack on the straights to increase top speed, the same as DRS in F1 season effectively.

Due to too many accidents with these high mounted wings and the lack of technology in materials, resulting in fatal fatalities for both spectator and driver alike. An all out banned was introduced, but after negotiations engineers and designers started to look at other areas of the car to create even more down force levels with the now restricted wing regulations.

Aerodynamics in Race Cars Explained - Aspects Of Race Car Aerodynamics - Ultimate Racing

Most of the principals applied where taken from aeronautical design and modified for use in Motorsport, with both failure and success depending on its application. Race teams normally have huge budgets and dedicated engineers striving to continually create more and more effective designs, all the while battle to gain the upper hand on regulations.

Sometimes we are only talking about 0. But over the course of a Race, this can make the difference between first and second place. As we can see the introduction of ground effects and down force has made a big impact on the world of motorsport.For a better understanding of aerodynamic testing, we asked an expert to provide us with some basic, but valuable information on the subject.

The author is directly involved in using his knowledge of aerodynamics in the design and manufacturing of airplanes.

His methodology must work or the plane will not fly. If we get it wrong, our race car is less efficient. If he gets it wrong, the plane crashes. We trust his approach to this because we know he has designed airplanes that fly very well. Aerodynamics start to have a more noticeable affect on a vehicle at around 50 mph. If you're traveling slower than 50 mph, the weight of the aerodynamic devices are probably more of a penalty than any perceived gain in performance.

Downforce and drag values go up roughly with the square of the increase in speed and the power required to overcome the drag forces goes up at a slightly steeper rate.

Scale models tested in smaller wind tunnels give less accurate data. Efficiency is affected by poor fit, surface roughness, waviness and other disturbances. Most aero engineers ignore efficiency and are real proud of the coefficient of lift and drag.

This line of thinking will steer you in the wrong direction when dealing with real world aerodynamics. As airflow separates from the surface of the vehicle, drag will go up at an increased rate beyond its normal drag curve, and lift will go down beyond its normal curve. The drivetrain shapes, tire friction, tire pressures, tire heat, racetrack surface irregularity, toe angle, front camber angle, rear alignment, rear toe, and rear camber all affect the aerodynamic efficiency for a race car and with that the horsepower needed to overcome drag.

It's easier to get a five horsepower gain in drag reduction than it is to squeeze 5 more horsepower out of the engine. For these reasons, drag and horsepower calculations for cars are not comparable to conventional equations that are intended for the design of aircraft.

If the data we get out of a test facility has to be manipulated, then it can be considered inaccurate data. If you manipulate the airflow, then the data is also inaccurate. The wind tunnel is designed to move air into and around a stationary vehicle. Keep in mind that we don't race in mph winds, we actually race at mph through relatively still air. It's a different set of dynamics between the two conditions.Downforce is a downwards lift force created by the aerodynamic characteristics of a vehicle.

The purpose of downforce is to allow a car to travel faster through a corner by increasing the vertical force on the tires, thus creating more grip. The same principle that allows an airplane to rise off the ground by creating lift from its wings is used in reverse to apply force that presses the race car against the surface of the track. This effect is referred to as "aerodynamic grip" and is distinguished from "mechanical grip", which is a function of the car's mass, tires, and suspension.

The creation of downforce by passive devices can be achieved only at the cost of increased aerodynamic drag or frictionand the optimum setup is almost always a compromise between the two. The aerodynamic setup for a car can vary considerably between race tracks, depending on the length of the straights and the types of corners.

Because it is a function of the flow of air over and under the car, downforce increases with the square of the car's speed and requires a certain minimum speed in order to produce a significant effect. Some cars have had rather unstable aerodynamics, such that a minor change in angle of attack or height of the vehicle can cause large changes in downforce.

In the very worst cases this can cause the car to experience lift, not downforce; for example, by passing over a bump on a track or slipstreaming over a crest: this could have some disastrous consequences, such as Peter Dumbreck 's Mercedes-Benz CLR in the 24 Hours of Le Manswhich flipped spectacularly after closely following a competitor car over a hump. Two primary components of a racing car can be used to create downforce when the car is travelling at racing speed:.

Most racing formulae have a ban on aerodynamic devices that can be adjusted during a race, except during pit stops. The downforce exerted by a wing is usually expressed as a function of its lift coefficient :. In certain ranges of operating conditions and when the wing is not stalled, the lift coefficient has a constant value: the downforce is then proportional to the square of airspeed.

In aerodynamics, it is usual to use the top-view projected area of the wing as a reference surface to define the lift coefficient.

The rounded and tapered shape of the top of the car is designed to slice through the air and minimize wind resistance. Detailed pieces of bodywork on top of the car can be added to allow a smooth flow of air to reach the downforce-creating elements i. The overall shape of a street car resembles an airplane wing. Almost all street cars have aerodynamic lift as a result of this shape. Looking at the profile of most street cars, the front bumper has the lowest ground clearance followed by the section between the front and rear tires, and followed yet by a rear bumper usually with the highest clearance.

Using this method, the air flowing under the front bumper will be constricted to a lower cross sectional area, and thus achieve a lower pressure. Additional downforce comes from the rake or angle of the vehicles' body, which directs the underside air up and creates a downward force, and increases the pressure on top of the car because the airflow direction comes closer to perpendicular to the surface.


Volume does not affect the air pressure because it is not an enclosed volume, despite the common misconception. Race cars will exemplify this effect by adding a rear diffuser to accelerate air under the car in front of the diffuser, and raise the air pressure behind it to lessen the car's wake.

Some cars, such as the DeltaWingdo not have wings, and generate all of their downforce through their body. The amount of downforce created by the wings or spoilers on a car is dependent primarily on two things:.Motor sports are all about maximum performance, to be the fastest is the absolute. There is nothing else.

To be faster you need power, but there is a limit to how much power you can put on the ground. To increase this limit, force to ground must be applied on the wheels. Increasing weight can do this, but weight makes handling worse and require more power.

downforce on race cars

So we need some virtual weight, we call it downforce and get it from airflow around the car. A wing can make a plane fly, but if we put it upside down, it can make a car NOT fly. Typically the term "lift" is used when talking about any kind of aerodynamically induced force acting on a surface. This is then given an indicator, either "positive lift" up or "negative lift" down as to its direction. In aerodynamics of ground racing cars, bikes, etc. The term "downforce", therefore, should always be implied as negative force, i.

Both the drag force and the downforce are proportional to the square of the velocity of a car. The drag force is given by:. Cl is the coefficient of lift, again determined by the exact shape of the car and its angle of attack. In current motor racing competitions, including Formula 1, DTM, Indy cars and Touring Car, aerodynamic downforce plays the most important role in the performance of the cars.

In the mid 's the use of soft rubber compounds and wider tires demonstrated that good road adhesion and hence cornering ability, was just as important as raw engine power in producing fast lap times. The tire width factor came as something of a surprise. In sliding friction between hard surfaces, the friction resistance force is independent of the contact area read about forensic science in braking here. It came as a similar surprise to find that the friction could be greater than the contact force between the two surfaces, apparently giving a coefficient greater than one.

The desire to further increase the tire adhesion led the major revolution in racing car design, the use of negative lift or 'downforce'. Since the tires lateral adhesion is roughly proportional to the downloading on it, or the friction between tire and road, adding aerodynamic downforce to the weight component improves the adhesion. Downforce also allows the tires to transmit a greater thrust force without wheel spin, increasing the maximum possible acceleration. Downforce, or negative lift, pushes the car onto the track.

It is said that at maximum speed, an F1 car produces 5 g's of downforce! Produced by almost every part of F1 car but mostly by use of diffuser and wings in the way that longer cord lenght is facing downward. Helping to induce more tire grip, but more downforce usually induce more drag. Downforce has to be balanced between front and rear, left and right.

downforce on race cars

We can easily achieve the balance between left and right by simple symmetry, so it will not be discussed. Front and rear is a different thing. Flow in the front greatly affects flow in the back of the car, and vice versa. Downforce must be adjusted according to racing track and behavior of the car.Join a community of over clever racing enthusiasts that want to improve their knowledge on the technical side of motorsport!

Race cars in general have a peculiar shape that distinguishes it from any road car on the planet. This shape might be different in each one of the wide range of motorsport categories around the world, but some aspects are still present, regardless of category. Have you ever wondered why? Aerodynamics is study of the forces and moments created by the interaction of air with a solid body, such as an airfoil.

It is a branch of fluid dynamics and relevant studies on the area began in the eighteenth century, but observations of fundamental phenomenon have been recorded much earlier. Most of the early efforts in understanding aerodynamics were directed to the development of heavier-than-air flight, which is the kind of flight that does not use buoyancy effects to generate lift forces.

Since then, the use of mathematical analysis, wind tunnel tests and computational simulation have evolved in an astonishing manner, helping aerodynamics to become crucial in many other fields. If the car has enough speed, it might be rather difficult for you to keep your hand pointing forward. Furthermore, you probably have heard of the disastrous consequences of tornadoes and hurricanes, which in short, are caused by wind interactions with solid objects.

A practical example of how important aerodynamic forces might be in motorsport environment, can be observed by comparing the cross-section of suspension wishbones of open-wheel race cars in 70s and nowadays. The recent cars have streamlined, airfoil-shaped wishbones, while the cars in the 70s have rough circular cross-section. Figure 1 shows the comparison between a small cylinder and a 10 times larger airfoil. It might be hard to believe, but both these shapes have the same drag.

To help improve your understanding of aerodynamics, let us first discuss some force definitions. Figure 2 shows a racing car with the three aerodynamic forces that arise around it.

Drag is the resultant of aerodynamic forces that acts in the longitudinal axis of the car, opposing its movement. This is a crucial element of aerodynamics study, and it is of primary concern in road cars aerodynamic design. It must be overcome by the tractive force generated by the engine. Lift is the resultant of aerodynamic forces that acts upward. Lift reduces the vertical forces of the car, and its reduction is of primary concern in racing car aerodynamics study. The opposite of lift is downforce, which is the resultant of aerodynamic forces that pushes the car against the ground.

Side Force is the resultant of aerodynamic forces that pushes the car sideways. This force is generated by lateral winds acting upon the vehicle. It is important for stability studies on road cars, but since lateral wind components are relatively small in racing vehicles, its importance is reduced in motorsport environment. Downforce generation has become one of the major performance-defining factors along with tyre development in the last 40 years or so. If you have read my previous article on lateral force generation by the tyres, the benefits of downforce will be clear: the amount of lateral force that can be generated by a tyre is extremely dependent on the vertical force acting upon it.

Simply put, the higher the vertical loads on a tyre, the higher the lateral force it can generate. One can think that the performance of a tyre can be improved by increasing the weight of the car, since it would augment the vertical load on the tyre, but this is not true.

As previously stated on the article about lateral weight transfer, the higher the weight of a car, the higher the weight transfer would be, and hence, the lateral force produced would be smaller. Also, a heavier car would require higher lateral forces to withstand the same lateral acceleration, and hence the benefit of higher vertical loads on the tyres is lost.

Furthermore, a heavier car would have less linear acceleration, and the overall effect would be lap time reduction. Aerodynamic downforce on the other hand, increases vertical load on tyres without much penalties, except for the commonly added drag that comes with it. The reason why race teams are favouring downforce generation instead of drag reduction, is that, even though straight-line speed are reduced, the speeds on corner increase so much, that the overall lap time is reduced.

Of course, the above is true depending on the race venue visited in the particular racing weekend, but it works for the major part of circuits. Notable exceptions are circuits where the straights or corners with large turn radius correspond to a much larger part of the circuit, like Monza, Spa-Francorchamps and Montreal tracks. This creates the need for variations of a car aerodynamic configuration along the season.It basically states that air pressure moving over a race car's various surfaces creates "downforce" or increased weight.

And while downforce increases tire grip and cornering speeds, there's a significant tradeoff -- greater downforce also increases drag, which reduces straightaway speeds [source: NASCAR. As a matter of fact; each participating manufacturer had its own somewhat unique and recognizable appearance. In recent years, however, NASCAR has attempted to even the playing field by standardizing the body shape race teams are allowed to bring to competition.

As a result, the bodywork of every NASCAR Sprint Cup race car is identical regardless of the manufacturer -- with the exception of the paint, of course. The design increases safety for the driver as the cars go faster and faster each year. But as the speeds increase, for safety's sake, the downforce has to increase as well. The additional downforce increases drag which acts to slow the car down. Well, it is. Richard Petty drove this Plymouth Superbird in the Daytona The Superbird's huge rear wing and pointed front end gave it a considerable aerodynamic advantage.

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