Front Aerodynamics
06-04-2003, 05:27 AM
#1
Racer
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Front Aerodynamics
Well I have quite a dilemma now. I went with the 9ff GT2 wing for my 03 C4S, but the car is kind of unsettling at high speeds. So I am being advised to go with a new front bumper. I am considering either the OEM GT2 or TechArt Front Spoiler II. Would like to get some more input from everyone else here on the board. If anyone has either of these two and is considering selling their's that would be great too. Seal Grey would be greatly appreciated. Thanks in advance.
06-04-2003, 11:56 AM
#2
Burning Brakes
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I love the look of the Techart II. It will lower your front end approx. 1"
The GT2 front will lower the front about .5"
You can get GT2 "replica" bumpers for $1700 or less. I believe the Techart is well over $3000.
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
The GT2 front will lower the front about .5"
You can get GT2 "replica" bumpers for $1700 or less. I believe the Techart is well over $3000.
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
06-04-2003, 09:14 PM
#5
Burning Brakes
Aerodynamics are a complicated thing. There are global effects and local effects. I will discuss some basics. By no means is this thorough, but at least it will give a general understanding.
Let us look at the case of a rear wing. We all know that the addition of a rear wing is supposed to increase downforce at the rear wheels. We also know that this increased downforce will increase traction. The increased traction is due to the equation F=N x u. I went into this in a previous post. Basically, the more weight you can add (N) to a surface to surface interface (tires on road) the greater the friction force (F). "u" is simply a coefficient of friction of rubber and pavement. But I am getting off the topic.
The reason there is an increased downforce due to a rear wing is because of an engineering parameter called a "moment". A moment is defined as a force multiplied by a distance (not a brief period of time as is the other definition!!). In this case it is the pitching moment (as compared to the yaw and roll moments). In the case of the rear wing, the force is the wind hitting it and the distance is roughly 1/2 of its perpendicular distance off the car's surface. So, if you were to weld a long metal flap to the tail of the car (RS America duck tail style) it would serve the same purpose.
If you don't grasp the concept of moment (pilots will), use this analogy. Draw a side view picture of your car on a piece of paper and draw an "X" right in the middle of it. Poke your pencil through the "X", lift the paper off the table and slowly twirl the pencil. You are applying a "moment" to the car.
Now, using the aforementioned analogy, consider the rear wheels will go down while the fronts go up due to the pencil twirling pitching moment. That means that the rear wheels receive more pressure while the fronts receive less.
So, the airstream over the car comes down the back window and hits the tail. Since the rear wing is located ABOVE the vertical center of the front projection of the car, it induces a pitching moment into the car that increases the load on the rear wheels while lightening the load on the front wheels. Keep in mind that the airstream has to make its way under the car too. If another "dam" can be placed BELOW the vertical center of the front projection of the car, an opposing pitching moment is induced (weighting the front wheels and lightening the rear wheels).
This brings us to wind tunnel testing. Porsche has spent countless hours wind tunnel testing all of their cars. to arrive at the optimum balance of speed and efficiency. If you read their literature, I am sure for legal reasons to avoid the exact effect that 03-C4S is experiencing, they will not sell their aerokit front and rear spoilers separately. Their respective sizes and shapes have been tweaked to work together to give the optimum result.
Remember, adding a big wing and air dam increase wind resistance while at the same time providing a combination of pitching moments to theoretically improve the traction. So it really becomes a delicate balancing act. Ask any F1 car designer. A great example is the Lamborghini Countach. The car's top speed is actually greater without the wing!
My recommendation after my little dissertation?? Try adding 9FF's front spoiler to compliment your 9FF tail. We as consumers must trust that these high performance tuners have at least tested their products on the road and ideally (probably rarely) in the wind tunnel and verified their performance as a system.
Good luck.
<img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />
Let us look at the case of a rear wing. We all know that the addition of a rear wing is supposed to increase downforce at the rear wheels. We also know that this increased downforce will increase traction. The increased traction is due to the equation F=N x u. I went into this in a previous post. Basically, the more weight you can add (N) to a surface to surface interface (tires on road) the greater the friction force (F). "u" is simply a coefficient of friction of rubber and pavement. But I am getting off the topic.
The reason there is an increased downforce due to a rear wing is because of an engineering parameter called a "moment". A moment is defined as a force multiplied by a distance (not a brief period of time as is the other definition!!). In this case it is the pitching moment (as compared to the yaw and roll moments). In the case of the rear wing, the force is the wind hitting it and the distance is roughly 1/2 of its perpendicular distance off the car's surface. So, if you were to weld a long metal flap to the tail of the car (RS America duck tail style) it would serve the same purpose.
If you don't grasp the concept of moment (pilots will), use this analogy. Draw a side view picture of your car on a piece of paper and draw an "X" right in the middle of it. Poke your pencil through the "X", lift the paper off the table and slowly twirl the pencil. You are applying a "moment" to the car.
Now, using the aforementioned analogy, consider the rear wheels will go down while the fronts go up due to the pencil twirling pitching moment. That means that the rear wheels receive more pressure while the fronts receive less.
So, the airstream over the car comes down the back window and hits the tail. Since the rear wing is located ABOVE the vertical center of the front projection of the car, it induces a pitching moment into the car that increases the load on the rear wheels while lightening the load on the front wheels. Keep in mind that the airstream has to make its way under the car too. If another "dam" can be placed BELOW the vertical center of the front projection of the car, an opposing pitching moment is induced (weighting the front wheels and lightening the rear wheels).
This brings us to wind tunnel testing. Porsche has spent countless hours wind tunnel testing all of their cars. to arrive at the optimum balance of speed and efficiency. If you read their literature, I am sure for legal reasons to avoid the exact effect that 03-C4S is experiencing, they will not sell their aerokit front and rear spoilers separately. Their respective sizes and shapes have been tweaked to work together to give the optimum result.
Remember, adding a big wing and air dam increase wind resistance while at the same time providing a combination of pitching moments to theoretically improve the traction. So it really becomes a delicate balancing act. Ask any F1 car designer. A great example is the Lamborghini Countach. The car's top speed is actually greater without the wing!
My recommendation after my little dissertation?? Try adding 9FF's front spoiler to compliment your 9FF tail. We as consumers must trust that these high performance tuners have at least tested their products on the road and ideally (probably rarely) in the wind tunnel and verified their performance as a system.
Good luck.
<img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />
06-04-2003, 11:00 PM
#6
Racer
Join Date: Jun 2001
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My note will be shorter than Ken's, but personally I would be reluctant to screw around with aftermarket rear wings, etc. Porsche has access to state of the art wind tunnel equipment, as well as the expertise to balance the competing parameters when fine tuning the aero effect of body treatment. Sure - you may make the car look cool, but at what risk of creating aerodynamic issues?
