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Old 10-01-2009, 08:36 PM   #1 (permalink)
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Smile Do Rear Spoilers / Wings Help Any?

No spam meant, but on this subject I did find a great website to have spoilers purchased, maybe installed on cars:

Car Spoilers including Rear Spoilers and Car Wings - Rear Wings and truck spoilers

Ok, I have an album of pictures showing my 2009 Chevy Cobalt LS Coupe XFE on file with my profile here that shows my spoiler clearly.



I bought the car out right after getting an insurance settlement for a very bad wreck I had, due to my brakes not working and almost getting me killed around a curve. I also got about $5,000 in discounts from GM, my father a GM Retiree, and the dealer that had my car on their lot. I must admit it is a strange feeling having a brand new car with no payments. And my insurance company did not wish to raise my rates nor drop me due to the conditions of the wreck- they did not seem to fault me. (it was my only wreck in my life, and I'm 44) But I was driving a med size 4X4 Chevy Colorado pickup truck that got around 17MPG (20 EPA)- this was rated BEFORE THE EPA REVISED THEIR METHODS OF SCORING MPG ON CARS/TRUCKS. I next got a sub-compact with EPA of 37 Highway 44 possible (as read on sticker on the window). What I am now experiencing is like culture shock. I can now drive to places on a gallon of gas that used to cost me over double that. I feel as if I have been freed from the chains of High Oil because of the vast improvement in mileage.

Back to the topic on hand:

I tried my best to find a Cobalt that had only 4 important requirements:

#1) It HAD to be an XFE
#2) I wanted the color RED (Because Chevy's "Blue" was far too dark for my tastes)
#3) The car HAD to have a rear spoiler.
#4) Spare Tire ($75 for the "doughnut")

The car was no longer in production for 2009, and the team was on break. So I had to pick from the car lots near my home state because XFEs were very rare, and I had no transportation and could not afford to wait months. I was working with a sales-guy and a dealership that I fully trusted due to all of the business my father had gave them over many years. I had many bad experiences with sales people treated me rudely or making assumptions that were false about me, so I was sticking with the dealership I was at. Finally my guy found a car fitting my description, only it also had the $40 option of an ashtray which was only a large ashtray shaped like a cup for the cup holder and a lighter plug for the socket (shesh)- So the car was strip down to standard options except for the ashtray and lighter (which I did not need and gave away), spare tire and jack and the almighty rear SPOILER. It does have many standard features that impressed me, yet things one takes for granted as being standard were not. It does have an awesome stereo system in it that was standard, and that means a lot to a guy that plays music such as myself.


The rear of my car reminds my a little bit of a 1985 Pontiac Fiero GT I once owned that had a spoiler on the rear. Or even a tiny bit like the back of a Corvette. I really likes the looks of a Cobalt Coupe better with the spoiler mounted, (the 2009 Sedan is another story), but I do not expect it helps my MPG any....

So, what do our EXPERTS here think? Generally speaking, or at least with a car like mine, do these stock mounted spoilers help the fuel efficiency even a little bit, or are they just for looks? Could they maybe HURT the mileage some because they are not as high up as real sports cars often have? - And there lays my beef: It seems like on the real expensive sports car, be they street legal or otherwise, their rear wing is normally mounted much higher than on stock cars like mine being sold.

I assume the rear spoiler on my car is at best good for looks, and at worse, it might even be a drag on efficiency.

Experts? (all please weigh in)

Thanks.


Last edited by Jammer; 10-02-2009 at 10:10 PM.. Reason: Added #4: The Spare Tire Option- I forgot that one!
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Old 10-01-2009, 08:51 PM   #2 (permalink)
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Old 10-01-2009, 09:13 PM   #3 (permalink)
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In general, a wing is good for traction and bad for economy. Because the racy image sells so many cars, wing-like things are sometimes used to help cure separated airflow over a rear window, which is good, but not as good as a plain fastback.
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Old 10-01-2009, 10:05 PM   #4 (permalink)
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Smile

Interesting. I was afraid that such a device might make the mileage worse.

Frank: Thanks for the tip. I had overlooked the Tips posted here. "my bad"

Still ' would like to learn about more thoughts on this subject.

Peace.
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Old 10-01-2009, 10:07 PM   #5 (permalink)
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Many efficient cars that have "spoilers" really just have deck lid lips/extensions to encourage flow off the trunk to separate cleanly, rather than curving partway down the rear of the car before separating (which increases both lift and drag).

So here's my GUESS: IF your trunk (without a spoiler) has attached flow at its end (and I'm guessing it does), and also a relatively sharp corner in the metalwork transition to the back of the car (no idea), then that raised spoiler probably hurts since it would increase the size of the trailing wake.

But that's only a guess. And unfortunately, I bet the difference would be small enough to be hard to detect in coastdown testing. But you could always try. That would give you a definitive answer.
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Old 10-02-2009, 02:08 AM   #6 (permalink)
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How to decide whether to remove rear spoiler to decrease drag, improve mileage.
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Old 10-02-2009, 02:27 AM   #7 (permalink)
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a quick google revieled an article claiming an 0.32 Cd for both the sedan and the coupe, seems high for the coupe as the cobalt is esentially the emerican equivalent of the opel astra G (same platform differnt body) the astra coupe has an 0.28Cd without a spoiler where the sedan has a 0.29.

the chevy seems to sit a little higher off the ground than the opel (possible softer american suspention vs the astra's hard euro setup?) and with FE not being so important for this type of car in the US (as you say yourself you doubled your milage with this car so chevrolet doesn't need to squeeze every last mpg out of it)

i think the spoiler might add 0.02 or so to the Cd, just a guess though....

loosing the spoiler is possibly the best for FE...beause "real" spoiler are only there to allow for extremely fast cornering wich doesn't matches well with FE driving anyway

than again, if you like it... just drive carefully with FE in mind and you should see a very decent milage on that car anyway
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Old 10-02-2009, 02:52 AM   #8 (permalink)
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Jammer -

I'd look into Bonneville Salt Flat cobalts for spoiler inspiration :

Top - 2006 Chevrolet at the Bonneville Salt Flats

Quote:
(from GM Press Release) Chevrolet Sets Three New Land Speed Records at the Bonneville Salt Flats GM Performance Division and its partners from So-Cal Speed Shop set three new land speed records with Ecotec-powered vehicles last week during the 58th Annual Speed Week event at the Bonneville Salt Flats in Wendover, Utah, including the first-ever Bonneville record using E85 ethanol. Ecotec-powered vehicles have now set eight records during the past four years with some form of GM involvement.
If I hade a coupe or sedan I'd spend more time researching this design. However, I can't say that this spoiler has any benefits. It could be for downforce or it could be to "mask" the parachute from the airstream. I just don't know.

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Old 10-02-2009, 03:20 AM   #9 (permalink)
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Carlos - Downforce. They use them in NHRA/IHRA as well.

I don't remember the whole reason they work, but I think I remember something about Bernoulli in there, or maybe I was day dreaming during that lecture. Either way, they're there to produce downforce.

OP - Check out the '99ish Pontiac Bonneville - that spoiler is for better aero, definitely. If it weren't there, the flow would curve sharply around the deck lid at the rear, funneling toward the center due to the overall shape of the deck area. It would be bad.

The spoiler, however, is probably neutrally helpful compared to the bare deck lid, since it's tilted up and it's a wierd shape/angle that I'm sure doesn't do much for aero at all.

The rear of the car seems almost perfect for aero from the rear windshield down, visually... it's not , but it seems that it is... if only they hadn't curved the deck lid like they did.
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Old 10-02-2009, 03:38 AM   #10 (permalink)
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Quote:
Originally Posted by lunarhighway View Post
loosing the spoiler is possibly the best for FE...beause "real" spoiler are only there to allow for extremely fast cornering wich doesn't matches well with FE driving anyway
I say: Take it off and use the mounting holes to secure a Kammback...

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