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Discussion Starter · #1 ·
As a newbie and potential buyer of a new Golf TDI or A3 TDI I have combed thru this Forum in an effort to educate myself as to various issues visa vis these vehicles. My sense at this time, is that in spite of the A3's apparent superiority in fit finish and componetry, ( 2 zone heating / AC, filters on cockpit air intake, leather seating, electric adjustable drivers seat ect. it seems a bit long in the tooth in its basic body shell design. Driver visibility is somewhat impaired by the high door sills, and consequent driver side mirror location ( although Audi seems to have recognized same with the lowered redesign in the 2011 model ) The manual transmission available in the Golf as well as the superior cd numbers .305 vs .32, and the basic 450 pound weight differential, given the same drive train, suggests to me, some MPG advantage as well.
Regarding these drag coefficient numbers I have a question or two:
Is there any information from VW GMBH available re basic aerodynamic design, and its potential for optimization? (It would be fun, and most educative, to see or hear about that phase of the vehicles design). And more specifically, are any of the available 'Body Gear Accessories', Front Valance (air dam?),Side Skirts, or the Rear Hatch Spoiler, really any kind of performance improvements on this cars basic design? Are there any numbers available? These optional extras, presumably would cut down aerodynamic lift, thereby improving traction (and weight) on the wheels. This should improve traction in the corners but does that weight at 65 mph compromise MPG ? Might these accessories provide any improvement? Is frontal area increased?
They might look cool but do they really work one way or another?
Are there any unseen advantages in the A3? Brakes?
Bill R.
 

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Discussion Starter · #5 ·
It's MPG not traction ?

Gentlemen, while I appreciate your responses, I still question, and wonder about, the addition of the lower air dam,side skirts - ( and rear hatch spoiler ?) as helps in upping MPG. While I can understand that they might increase performance, add stability, and maximize adhesion at speed, ( increasing down force by lowering aerodynamic lift,) would not the overall weight on the wheels be increased somewhat ? Then would not the MPG be compromised? If it's true that a lighter vehicle is more easily propelled down the road, and thus requires less energy, would not the heavier vehicle ( that with increased downforce ) require more?
If this is true the above VW 'Genuine Volkswagen Accessories' become cosmetic go-fast adornments and would not in fact contribute to the increase in MPG. Do I have this right ?
Thanks for your interest.
Bill
 

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Discussion Starter · #7 ·
Aero Info Continued

My question answered ?
With respect to the addition of ground effects air dams and rear roof wings/ foils and the addition of drag and consequent loss of MPG, see a you tube video at

http://audimobiles.com/2010/01/07/audi-aerodynamics-of-planes-and-cars

or just google audi-aerodynamics of planes and cars.
It claims that a certain race car, complete with all the, adjustable, race car trim, air dams, wings etc. tested out in their wind tunnel, shows figures that demonstrate that the car running at 135 MPH, can produce enough down force,that it could run on the ceiling of the wind tunnel ! Down force it would seem, is a major addition of weight, ideal for tractive forces in corners etc, but not contributory to great fuel economy.
I would expect that VW has optimized the cars aero characteristics as currently designed and manufactured, in an effort to qualify it for maximum MPG. The addition of foils, air dams, rear deck lid spoilers, lowering of the car, etc. which might provide additional ' down force', and traction on the track would not, it would seem, contribute ( indeed would detract from ), toward MPG, and straight out down the road performance.
Bill
 

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Discussion Starter · #9 ·
NJ2dc,
You are spot on right. But you'd need a wind tunnel to verify same.

But my point re the question of adding after market aero tuning bits, is that while they might give some added down force, they will probably compromise the OEM, wind tunnel optimized, body shape, resulting in increased drag and consequent diminishment of MPG and acceleration.
One could add a big wing on the back of a Prius. Do you think the cd would go down? There is a wager I'd like to place.
Bill
 

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Discussion Starter · #11 ·
Optimization

Glennco,
I think I'll have to disagree re VW not having done all they could.
Audi and VW have invested many millions of $'s / Euros, on the construction of ( their own ) wind tunnels and the attendant science involved in the optimization of the aerodynamic shapes of their vehicles. In addition, governments and cultures around the world, on becoming more aware of the impact of the use and diminishment of fossil fuels, are placing greater and greater demands on manufacturers to get their products to go further on the fuels they are burning.
VW, I'm sure, could have decided to design and produce, a Prius like camback, but their problem definition and product program called for a vehicle of greater volume and superior drivability. Given that mandate they put their models through their wind tunnels to get them as smooth as they were able, to maximize their performance, and improve efficiencies to the extent they could.
This has been an evolutionary process going all the way back to the Giugiaro 70's Rabbit, and like Porsche's 911, has resulted in a car that in my mind is pretty near optimal. I expect that future models / and design will give up some of their volume and probably engine size, they will become even lighter ( more aluminum/plastics/carbon fiber ), and they will get lower with lower cd's, and maybe even start to morph into a Prius like shape. But we will have to wait a while for that.
I'm a believer I guess.
Bill:bowdown
 
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