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Old 03-29-2008, 08:48 AM   #11 (permalink)
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I wouldn't say the Civic and Focus are similar at all, aside from the fact that they're both hatchbacks. 3 major differences that stand out: the Civic has significantly more rear taper in plan & profile than the Focus, and its height is less than the Focus as well. The Civic's roofline also extends much further to the rear of the vehicle than the Focus.

If you're going to be skeptical of all published Cd figures, then your only solution is to do it yourself. Since you don't have a wind tunnel, you can figure it out via coast-down testing:

http://www.instructables.com/id/Meas...t-of-your-car/

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Old 03-29-2008, 11:03 AM   #12 (permalink)
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Allpar.com and a few car review sites list the Shadow as having a .42 cd. That mayfield site list a plymouth sundance (same car) as .36, and a Shadow Shelby CSX as .32, not sure where the improvements are besides maybe being a 2 door. Wikipedia also shows the sundance at .42.
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Old 03-29-2008, 12:24 PM   #13 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
If you're going to be skeptical of all published Cd figures, then your only solution is to do it yourself.
[/URL]
Andrew J Figured in the .Cd of his hatch at .33 On the front page of Ecomodder is the article on the Aerocivic " How to drop your .Cd from .34 to .17 .

Andrew J :
"
I did 2 of 6 runs of coastdown testing in "stock" form to verify that the Excel spreadsheet was giving me decent numbers. By comparing the Cd that the spreadsheet gave me with Honda's Cd of 0.33 for a stock 5th generation Civic hatchback, I can see how far off (if any) the numbers in the spreadsheet are. "

Road & Track gives the figure at .31 for the hatch and a little less ( unspecified ) for the VX.

I 'm just really confused at which is correct.

Since I have a 5th generation hatch, I'd like to believe that the stock .Cd is .31.

That would mean that Andrews' .Cd would actually be even lower than he says ( which would make him happy I would think. )
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Old 03-29-2008, 03:26 PM   #14 (permalink)
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Quote:
Originally Posted by .Cd View Post
That would mean that Andrews' .Cd would actually be even lower than he says ( which would make him happy I would think. )
You'd think correctly

While I'd be thrilled to know that a stock 5thGen hatch (non VX) has a Cd of .31, I'm not gonna put any money on it.

Here are the numbers I've seen:
0.33
0.32
0.31

We all know that the VX has slightly better aero with the passenger mirror delete and the rear undertray thingie, so that's where (I belive) the 0.31 is coming from.

So that leaves .32 and .33 for the non VX 5th gen's.

Personally, I'd tend to be a bit more conservative, so I'd go with .33 for the rest of the 5th gen hatches.

Either way, it's all just semantics. Figuring out your EXACT Cd isn't going to make your car any more (or less) aerodynamic.
It just gives you a starting point from which to improve
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Old 03-29-2008, 04:18 PM   #15 (permalink)
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Cds

My braincell fired again.EPA,Ann Arbor,Michigan,does the new car certification testing for all vehicles in the U.S. The carmakers,I believe,are supposed to provide the EPA with drag data so they can properly load the dynomometers they use in the testing.Perhaps you can GOOGLE the USGOV,and get a hold of the EPA folks for the numbers.Also,CAR and DRIVER Magazine has been the most comprehensive lay publication to provide such data.Check 'em out at the library.They also provide frontal area,and drag factors for selected models each month.They also have access to Chrysler Proving Grounds,East Chelsea,Michigan,and do comprehensive roadtests,including,drag-limited top speeds,something of great interest to tunnel-heads.
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Old 03-30-2008, 10:13 AM   #16 (permalink)
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Quote:
Originally Posted by AndrewJ View Post
You'd think correctly

While I'd be thrilled to know that a stock 5thGen hatch (non VX) has a Cd of .31, I'm not gonna put any money on it.

Here are the numbers I've seen:
0.33
0.32
0.31

We all know that the VX has slightly better aero with the passenger mirror delete and the rear undertray thingie, so that's where (I belive) the 0.31 is coming from.


The Road & Track article ( I'll have to find the issue ) stated that the VX was actually slightly lower than .31 , but did not give an exact amount.
The sedan was a .32 which has always puzzled me, since I would think that the wake would be much smaller on a sedan.

Darin, I sensed that you were a little angry at my post earlier concerning trust of published .Cd figures.
I wasn't saying anyone here was lying about their .Cd, but rather that I was wondering how reliable that published .Cd figures are since, as we have seen, they tend to flutuate even from professional sources.
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Last edited by AndrewJ; 03-30-2008 at 06:23 PM..
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Old 03-30-2008, 04:41 PM   #17 (permalink)
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No, at all angry. It just seems kind of unproductive to spend much time wondering which of the published stats are exactly right.

Paraphrasing Andrew, the key thing is the relative improvement we can make to our cars.
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Old 04-19-2008, 03:33 PM   #18 (permalink)
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The Vx will have a wagon type wake,of generally homogeneous makeup.The sedan may produce counter-rotating vortices off the back of the trunk,with higher induced drag,requiring a longer period for viscous attrition to wear them down,all paid for by underhood power and fuel.Each body style has it's own merits,however in the case of the Civics,it looks like the wagon edges out the notchback by a nose.Hucho's book has images of all wake forms and is sure worth the look!
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Old 04-24-2008, 04:39 PM   #19 (permalink)
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What i dont think some people understand is that bigger items of a simular shape have a smaller cd. examples are a 50 cal bullet versus a 22 cal bullet. or a train vs a car. a train gets a very low cd. thats why u need to add the area into the mix

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