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Discussion Starter #1
Aerodynamic improvements

According to reports Audi originally heard that Renault were building a 3 ltr car. Audi were concerned that Renault may steal the eco lime light. Some time later Audi realised that that they didn’t need to worry, they were thinking on very different lines…
Renault 3ltr V6 Clio

Audi A2 1.2TDI 3Ltr/100km. (2.99 Ltr/100km to be exact)

Progress from the wind tunnel
Audi's engineers have reduced the drag coefficient of the A2 1.2 TDI to a sensationally low cD = 0.25 - making the three-litre version the most aerodynamically efficient of any production passenger car. As when optimizing the weight, this achievement can be expressed as a clear-cut equation: excellent basis + fine-tuning of detail features = Advancement Through Technology.
The body shape of the Audi A2 is characterized by lines tapering to the rear, and is thus reminiscent of one of the most aerodynamically effective shapes, the droplet. The generous amount of space for rear passengers comes as something of a surprise when one considers how sleek the car's exterior is. This is all thanks to a further highlight of the A2 body, the Space Floor Concept. The rear footwells are sunk into the floor and therefore 13 centimetres lower than the front footwells; this allows rear passengers to find an ergonomically good, relaxed seated position, making the rear seats superior even to many a larger, nominally more spacious car.
For the Audi A2 owner this is a good thing, additional parts that were intended to make the 4 seater slip through the air are available to retro fit to your A2 (sort of). A German forum member as been creating various mods to make the underside of the A2 cut through the air to increase fuel economy. as well as retro fittng the 1.2 Aero mods from Audi
As a percentage of the total drag coefficient of 0.29 (this is a very good drag coefficient but the A2 is even better!) the various elements that make up this drag are:
Parts Percentage of Total Drag
Cooling package (including radiator, intercooler, oil cooler, etc) 33.4%
Exterior 31.7%
Front wheels 13.1%
Rear wheels 6.9%
Floor 6.9%
Rear Axle 3.1%
Engine 3.1%
Front Suspension 1.4%
Exhaust 0.7%
Modification % Change
Lowering the vehicle by 30mm approx. -5
Smooth wheel covers -1 to -3
Wide tires +2 to +4
Windows flush with exterior approx. -1
Sealing body gaps -2 to -5
Underbody panels -1 to -7
Concealed headlamps +3 to +10
Outside rearview mirrors +2 to +5
Airflow into the enginecompartment +4 to +14
Brake cooling devices +2 to +5
Interior ventilation approx. +1
Open windows approx. +5
Open sunroof approx. +2
Roof-mounted surfboard rack approx. +40
In the last 10 years we have been producing style over function, which is something most are prepared to trade for the looks. However 30% of your engine power is used to push you car through the air, make your car slippery in the air and you will see results
2.10 - A smooth brick
0.90 - A typical bicycle plus cyclist
0.70 - A Formula 1 car (avg according to track)
0.70 - Caterham Seven
0.60 - A typical pick up truck
0.57 - Hummer H2, 2003
0.51 - Citron 2CV
0.42 - Lamborghini Countach, 1974
0.39 - Dodge Durango, 2004
0.38 - Volkswagen Beetle
0.38 - Mazda Miata, 1989
0.37 - Clio V6 3ltr
0.37 - Ferrari F50, 1996
0.36 - Citron DS, 1955
0.36 - Ferrari Testarossa, 1986
0.36 - Opel GT, 1969
0.36 - Citron CX, 1974
0.35 - BMW Mini
0.34 - Ford Sierra, 1982
0.34 - Audi TT Mk1
0.34 - Ferrari F40, 1987
0.34 - Chevrolet Caprice, 1996
0.33 - Chevrolet Camaro, 1995
0.33 - Dodge Charger, 2006
0.33 - Audi A3, 2006
0.33 - Subaru Impreza WRX STi, 2004
0.32 - Toyota Celica, 2005
0.32 - Ford Focus 1998
0.31 - Audi A3 2003
0.31 - Citron GSA, 1980
0.30 - Saab 92, 1947
0.30 - Audi 100, 1983
0.30 - Audi TT Mk2 (with a wider and larger frontal area)
0.30 - Porsche 996, 1997
0.29 - Honda CRX HF 1988
0.29 - Subaru XT, 1985
0.29 - BMW 8 Series, 1989
0.29 - Porsche Boxster, 2005
0.29 - Chevrolet Corvette, 2005
0.29 - Honda Accord Hybrid, 2005
0.29 - Lotus Elite, 1958
0.28 - Porsche 997, 2004
0.28 – Audi A2 (not 1.2 model)
0.27 - Infiniti G35, 2002 (0.26 with "aero package")
0.27 - Mercedes-Benz W203 C-Class Sedan, 2001 - 2007
0.26 - Toyota Prius, 2004
0.25 - Honda Insight, 1999
0.25 – Audi A2 1.2 model
0.19 - Mercedes-Benz "Bionic Car" Concept, 2005
0.137 - Ford Probe V prototype, 1985
0.15 - Volkswagen ARVW
0.06 - The boxfish
0.04 - A drop of water
I decided to fit these 1.2 aero modifications to my car after suggestions from a German A2 owner as they are applicable to the A2 1.2 TDI designed to cut through the air with a low drag coefficient. I have also decided to fit wheel deflectors to the rear wheels to reduce wake and drag.

Further aero improvements to come...
Information taken from articles relating to improving Aero dynamics.
Modified by emm at 4:53 AM 8-20-2008

Modified by emm at 6:31 AM 8-20-2008

Modified by emm at 6:32 AM 8-20-2008

273 Posts
Discussion Starter #2
Re: Aerodynamic improvements (emm)

After reading about the amount of drag created by the rear wheels I decided to investigate further, I. viewed a few pics from a German A2 owner, and decided to go for it. Many cars now fit rear wheel deflectors Lexus, BMW, VAG, etc

As a lot of drag is created from the rear wheels, so I wanted to make a rear wheel deflector to disrupt air that was inevitably hitting the tyres. But not make it to big to deflect the air out. I didn’t want to create wake and therefore further drag, or too much turbulence under the front of the rear arch . Too much turbulence under the arch next to the floor would have created lift at high speed.
The location points and basic plate in place
This is what I came up with. I used 2mm thick Plastic board in black after making a template.

I then added a slightly larger radius on the outside edge to reduce turbulence further.

Finished and fitted, as you can see I didn't want it to extend to the outside edge due to wake. Although I might revise this slightly and add a further radius to blend the smooth natural wheel arch curve and the deflector.
I revised the rear wheel deflector down to 20mm exposed below the front of the rear arch.

I also noticed that while the rear of the car is flat with most of the parts back from the rear axle onwards covered. On the off side of the car, along with the middle Audi fitted a complete panel to smooth off the underside and put ribs in it to improve air flow, however they left the part near the exhaust. Not sure why, as its possible to make plastics to withstand the heat. The result was a big area next to the tail pipe that left the rear bumper exposed and acting like a parachute on the near side for air flow past the exhaust.
This area could be improved. I bought some black corrugated plastic or Correx for its flexibility, strength and weight. (It’s as light as paper). Oh as it’s fairly heat resistant, After much fabrication with card i finally cut some pieces and fitted them.

The result with all the added aero parts added is 67mpg on the DIS and about 62-63mpg on paper. Up from about 55-58mpg so while not huge its enough to make we think its worth the hassle, they also didn’t cost very much only a few quid here and there. I will keep an eye on the fuel economy to see if its effected by various types of driving, including winds, temp and type of journeys.

Modified by emm at 4:52 AM 8-20-2008
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