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Old 08-17-2001, 04:15 AM   #1
fungo phil
Question What is the function of a "waist spoiler"

A couple of weeks ago there was a thread concerning the installation of a waist spoiler. The last post in the thread asked what the functionality of the spoiler was and the question was never responded to. Other than a place to set your beer during a tailgate party what is the fuctionality of a waist spoiler and how does it work, especially when it has a roof spoiler just above it? Anybody?
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Old 08-17-2001, 09:34 AM   #2
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It looks cool, that's about it. A spoiler has to be in an area where air actually hits it for it to do something.
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Old 08-17-2001, 12:39 PM   #3
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agree with ridinlow. it sure does looks pretty though
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Old 08-17-2001, 12:49 PM   #4
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1997 subaru
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You know i would buy one if it wasn't so much money. I have been waiting for someone to sell one,
But i think subaru selld them for what...500 bux. I paid that much for a SYMS rear wing
They do look bad-ass though and it totally accent the wagons.
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Old 08-17-2001, 01:41 PM   #5
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At high speeds (racetrack speeds, or "GT3 speeds" for some people) a waist spoiler would presumably provide some aerodynamic benefit (downforce, stability, etc.) You shouldn't be reaching those speeds on public roads.

Subaru of America would probably say (like they said about the hoodscoop on last-gen 2.5RS and OBS): "Sure it's functional. It's function is stylistic."

I think the function of a waist spoiler is to waste your money.
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Old 08-17-2001, 01:51 PM   #6
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The first problem you all have is spelling..... it is a WASTE spoiler, not a Waist spoiler. With that spelling you can see its purpose.


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Old 08-17-2001, 02:52 PM   #7
Jon [in CT]
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02 WRX Sedan


It obviously serves the same purpose as the 2.5 RS hood scoop.
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Old 08-17-2001, 03:01 PM   #8
fungo phil

Right, it is a "WASTE" your $$$ spoiler. And at race track speeds that thing would be sitting in an aerodynamic vacuum in the slip stream of the wagon, totally useless except for that occasional beer can.
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Old 08-17-2001, 04:10 PM   #9
Travis R
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I don't usually give in to the aesthetic mods (side skirts, lip spoilers, etc), but this is the one "visual" option that will have on my wagon. I can't rationaly explain why I like it. I just looks awesome.
You're right though, probably no aerodynamic difference.
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Old 08-17-2001, 04:46 PM   #10
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I really like it with the Subaru wagon body kit, but not alone. And being fond of stealth, though I was blown away by the wagon pix from a Euro auto show, in real life, I love the looks of my wagon.

I don't think that the waist spoiler has any benefits aerodynamically, though when you imagine air flow over the wagon, it might have some benefit at triple-digit velocities.

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Old 08-17-2001, 05:29 PM   #11
Default I can't take the credit for this but..

... Someone else on another forum mentioned how small the Audi TT spoiler was, but it was just enough to solve their light tail problem. I thought it was an exellent observation.
An aerodynamic mod does not have to grab the air and strangle it or wrestle it to do some good. Even pushing down on the trunk lid which in turn pushes down on the trunk lid stops ( little rubber feet) actually effects the car. sometimes this is all it takes to clear up some light tail issues. on the other hand my MY98 coupe wing removed added ten mph top end.
I always liked the look of the wagon with wings and w/out rack. someday I will gut my coupe and put it all in a wagon.
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Old 08-17-2001, 06:36 PM   #12
Eric SS
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Actually it does have some functionality. It can actually help keep your rear windshield clean and easier to see through.

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Old 08-17-2001, 07:48 PM   #13
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I don't see what the big deal is. It's perfectly functional ... knock out the windshield and the back window it'll work fine.


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Old 08-18-2001, 04:12 AM   #14
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Default What???

Someone post a pic of this relleged waist spoiler.
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Old 08-18-2001, 12:46 PM   #15
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Curious to see what a waste spoiler looks. Pics please.
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Old 08-18-2001, 03:59 PM   #16
Jon [in CT]
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It's the spoiler just BELOW the rear window:
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Old 08-18-2001, 04:09 PM   #17
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$500 bucks fr that???? looks good but not 500 worth.
my two cents
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Old 08-18-2001, 09:56 PM   #18
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it covers up the only ugly piece of sheet metal on the wagon

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Old 08-19-2001, 01:03 AM   #19
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You are wrong about the waist spoiler on the WRX wagon. I find it entertaining how snide everyone becomes when they make idiotic assumptions based on ZERO scientific fact. No offense toward any of you personally, just pointing it out.

2 points:

First, the Impreza "wagon" shape is actually more of a euro "5 door" design, meaning a 4 door hatchback. Traditionally, wagons had a very vertical rear surface, but that is not even remotely true on this vehicle. There is a significant slant to the rear window and a pronounced rear decklid where the waist spoiler mounts. There is far more airflow here than you think. As the entire shape of the vehicle is very winglike, any inverted wing surfaces are quite advantageous in reducing lift.

Second, as air passes over the top of the vehicle, it has a tendency to spin over the trailing edge of the roof and create a vortex against the back window, a low pressure area that induces a significant amount of drag on the vehicle at even mild speeds. The location and design of the roof spoiler plays on this tendency, the large opening between the roof and the wing surface allows passing air to create a low pressure area against the bottom of the wing as it begins to rotate downward. If the wing were contiguous with the roof, it would only increase the magnitude of the vortices and provide very little downforce. The waist spoiler helps to foil the air once it has begun to spin downward, and prevents it from "pooling" at the back of the car in a low pressure zone. The new bridge type waist spoiler for the new body style wagon also extends slightly on either side of the body, helping to draw air in a more controlled manner around the back of the car and across the wing surface.

I think it would be very interesting to see the air behavior around the back of the wagon in a wind tunnel. I remember reading that when engineers added a very slight lip to the edge of the trunklid of the Saab 9-5, it reduced overall drag by almost 15%, purely by reducing the tendency of the air to vortex. The difference was less than 1/4 inch. Fluid dynamics are an amazingly powerful thing, it dissapoints me that so many people on the board try to discount them as only significant at extreme speeds. Aerodynamics plays a role at ANY speed, and a much larger one than people give it credit for. It can drastically affect the handling and performance of a vehicle, even at modest speeds.

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Old 08-19-2001, 01:58 AM   #20
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How about the spoiler that replaces the OEM one but sits a few inches taller than the roof? What do you guys think of that one? Who sells them?
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Old 08-19-2001, 10:14 AM   #21
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I'd be interested to see if anyone has driven in the rain with a waist spoiler. I remember seeing pictures of perfectly still beads of water on the 2.5RS coupe's wing, while the car was at speed.
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Old 08-19-2001, 10:48 AM   #22
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This is easy enough to check if it is functional or just for Fun. Someone that has one tape a several rows of small pieces of yarn on the top of the spoiler. Have someone sitting in the back or video tape it. Bring the car up to speed and observe the yarn. If they just sit there and dont fly around, Then it is just for looks and Porters theory might not be true. If they are swirling and flapping around then it is smoothing out the air flow on the bottom edge, actually performing a function.
I do not think that any air will be acting upon it personally. IIRC a rear window area of an auto that is around 23 degrees or less, will allow the air to flow over the surface almost sticking to it. Angles greater than 23 will cause the air to flow over and cause a vacuum in its void. Imagine a semi truck here folks.
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Old 08-19-2001, 02:11 PM   #23
FuJi K
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here's a effect...............

it makes your REX look faster
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