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Old 11-28-2016, 05:43 PM   #1 (permalink)
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Should I fit a rear spoiler like most modern cars?

I notice most new cars these days that have a steep rear window (estates/station wagons etc.) have a spoiler above the rear window.

Am I wrong in assuming they have fuel economy aero benefits, as well as being for styling?

Is it worth me putting one on my old '94 Citroen BX (same as photo but I don't have roofracks)?

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Old 11-28-2016, 06:42 PM   #2 (permalink)
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If you could find Cd data on a comparable model with and without a spoiler that would hint as to how much the Cd dropped. Better still would be fuel economy ratings for otherwise identical models.

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Old 11-29-2016, 07:59 AM   #3 (permalink)
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Try searching for kamm back or kammback and read about what others have done on here.

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Old 11-29-2016, 08:33 AM   #4 (permalink)
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If the factories wanted an aero benefit, the spoiler would be larger. They're looking for styling and an easy way to mount the third brake light.

Originally Posted by sheepdog44 View Post
Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
Automatic .........................86%

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Old 11-29-2016, 08:50 AM   #5 (permalink)
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Been looking at kammbacks but not prepared to go that big just yet. The one above does look very nicely made, though. I guess even if the stock spoilers do have any aero benefit, it'll be tiny.
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Old 11-29-2016, 09:10 AM   #6 (permalink)
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We looked at the Chevrolet Sonic Hatchback "Z-spec" wing (a Chevrolet part) for a project at work.

We could see no difference in coastdown times using a level test track in both directions.
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Old 11-29-2016, 12:45 PM   #7 (permalink)
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The idiom around here is 'small potatoes'. If you are worried about what you neighbors think, consider the underside — diverter/skirts/diffuser.

The worst angle for the rear glass is 30. From Morelli's research a chamfered ring around the whole rear end is helpful.
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Old 11-30-2016, 07:51 AM   #8 (permalink)
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Giving the air a clean sharp edge for the air to release from is important, but more important is the baby steps manufacturers are taking as the public becomes more accepting of them.

These devices are becoming larger and more elaborate ever year, only the automatic car washes will limit their scale.

I think it's a nice way to customize your car if nothing else.

To notice a real affect in a coast/roll down test, I suspect one would have to be rather large.

As a side note, the Chevy Cruze hatch went for down-force over lower Cd, must be a marketing thing.


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Last edited by kach22i; 11-30-2016 at 07:59 AM..
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Old 12-01-2016, 01:53 AM   #9 (permalink)
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I noticed this feature on just about every make and mode of cars trucks wagons vans . After I built my Atro Tonto. Witch has one of theas that extends 8"past the tailgate. For me the tailgate ark determined how much I was able to drop below the top of the bed(what angle I could use), and clear the gate.

Ford even took advantage of the extra space in the tailgate to add a fold out lader.
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Old 12-03-2016, 01:34 PM   #10 (permalink)
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there are some rear angles to avoid which can lead to bistable flow,booming,and increased drag.It's complicated

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