Instability at higher speeds... - Page 2
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This is a discussion on Instability at higher speeds... within the Suspension & Wheels forums, part of the Tech & Modifying & General Repairs category; First thing one has to remember is that the WRX has 6" of ground clearance, you won't find many cars ...

  1. #16
    Moderating on the run! Big Sky WRX's Avatar
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    First thing one has to remember is that the WRX has 6" of ground clearance, you won't find many cars near that. I think this is the largest contributors to instability in the wind. Lowering the car will help some. Aero bits as well.

    If you experience high speed instability (other than wind effects) common "cures" include increasing caster and using toe in (front/rear).

    I've never had much problem w/ wind (and believe me Eastern Montana is famous- infamous? for wind) knock on wood

    Big Sky
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  3. #17
    Registered User Racenut's Avatar
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    haha... you should come drive my 78 Dodge motorhome down the highway with a crosswind
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  4. #18
    Registered User Rich10's Avatar
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    I haven't felt this wind instability since I went to shorter and stiffer springs (Eibach).
    2002 WRX WRB
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  5. #19
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    Now that we are talking about aurodynamics, wings and front lips.. Anyone have some info about the oem rear underspoilers (diffusors) does it generate any downforce and or less drag or is it just for looks?

    And what effect will it have to add a flat stainless steel or CF rally protection plate under the car?

    I'm asking because I want maximum downforce and stability in high speeds.
    Silver -02 Impreza WRX
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  6. #20
    Registered User bluerex47's Avatar
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    isn't the oem diffuser just the bumper and only there for looks? to have any significant effect, the diffuser needs to go under the car a little ways. i have no clue as to what help it will provide and how far under the car it should go, but it can be done easily and will add some downforce. simple aluminum sheets placed right could do it. but then, all i've seen is some open wheel scca cars doing this, and i am by no means an aerodynamic guru, just adding my .02
    - chris
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  7. #21
    Registered User SonicYellowWRX's Avatar
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    Quote Originally Posted by Roffa
    And what effect will it have to add a flat stainless steel or CF rally protection plate under the car?

    I'm asking because I want maximum downforce and stability in high speeds.
    Well, this makes a huge difference in aerodynamics... the flatter the bottom, the less lift you have. The Prodrive lip actually extends underneath the bumper a little to reduce lift and add downforce and that is how it is achieved. Simply lowering the car will make a difference though as air flow under the car is decreased, and the lips that extend to the ground work on this principle.
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    What bridge was this?

    The other i drove into CT and it was pretty windy....i thought i was getting a flat cuz it felt like my car was pulling....i've been in more stormy and windy days on bridges but never enough to allow my car to get pulled halfway into another lane....
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  9. #23
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    Quote Originally Posted by SonicYellowWRX
    Well, this makes a huge difference in aerodynamics... the flatter the bottom, the less lift you have. The Prodrive lip actually extends underneath the bumper a little to reduce lift and add downforce and that is how it is achieved. Simply lowering the car will make a difference though as air flow under the car is decreased, and the lips that extend to the ground work on this principle.
    But do you want a flat plate or is a custom shaped plate better.. I'm thinking a plate with low front and side that goes slightly up in the middle creating a vacume underneet.. !?

    I have heard some F1 cars does this.. I'm afraid of putting on a flat plate under almost the complete car would mess up aerodynamics and make it unstable in higher speeds 110+mph. Or can I make more DF by using diffusors and custom undercar plates?

    I have read that on the new ferrari the rear diffusor makes 160lbs of DF @ 185mph
    Silver -02 Impreza WRX
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  10. #24
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    There is a thread by the boys at prodrive about the stock wing for the wrx on NASIOC. It is not a downforce-creating wing.

    What it does is cause the car to have zero lift at the back... just as the aerodynamic aids for the G35 do as well. Coupled with the front aero kit, and you have an excellent combination for stability at speed.The wing on the STi is for downforce though.

    I have the full subaru aerokit on my car, and coupled with my coilovers, the car feels rock solid at all speeds I have dared to push the car to.
    02 WRX WRBP sedan..
    Upgrades??? stock...
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  11. #25
    Registered User 02bug'n's Avatar
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    yesterday driving home to west virginia my car was being pushed around side the side in my lane like a little kid at school getting picked on by bullies. i first thought my tire or something was getting low, because it was pretty low after a few days of driving on it a few weeks ago. but that wasn't the problem i checked my tire pressure at a rest area and it was good...so therefore i knew it was the wind...because it was pretty windy yesterday driving through the mountains.

    i guess i'm just posting this to show another issue of "instability" from gusts of wind hitting the rex at the side.

    can't wait till march, gonna lower her and get a new set of rims/tires....that should solve the problem.
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  12. #26
    Registered User SonicYellowWRX's Avatar
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    Quote Originally Posted by Roffa
    But do you want a flat plate or is a custom shaped plate better.. I'm thinking a plate with low front and side that goes slightly up in the middle creating a vacume underneet.. !?

    I have heard some F1 cars does this.. I'm afraid of putting on a flat plate under almost the complete car would mess up aerodynamics and make it unstable in higher speeds 110+mph. Or can I make more DF by using diffusors and custom undercar plates?

    I have read that on the new ferrari the rear diffusor makes 160lbs of DF @ 185mph
    Its hard to explain fully and accurately, but try searching the net for aerodynamics... basically you want air to travel at a slower rate over the car than the air travelling under the car. That is what produces downforce and that is what dictates the shape of a car, however, the bottom cannot be perfectly flat cuz of wheels, drivetrain, exhaust, etc.

    As for your idea with varying the underside plates, I think I know what you are getting at, but you're slightly confused. F1 cars and such utilize ducting that are based on the "Bernoulli effect", which is very basically explained with a garden hose flowing water slowly, but when you put your finger over the nozzle, the water sprays further due to the high pressure that was produced. This high pressure gives you the suction effect or vaccuum on automotive applications.

    Aerodynamics is a complicated field though and applying them to a car without proper testing is pretty much hit or miss. Information isnt widely available about the subaru WRC cars, but a flat as possible bottom + the intercooler/ radiator ducting up through the vent in the hood is as important as the bumper, fenders, and wing. The key is balance... just to reference the Prodrive Aero Pack/ UK300 aero pack, the front lip, with its little lip extending below the car for a flat front underbody, upsets the balance greatly! Just to be safe, I would get the Prodrive Aero Pack or any race oriented aero kit like C-West. (but you probably need the whole kit + wing that they run on their race cars)
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  13. #27
    Moderating on the run! Big Sky WRX's Avatar
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    These are oem jdm under pieces- looks like they take aero efforts a little more serious than SOA





    Big Sky
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  14. #28
    Registered User SonicYellowWRX's Avatar
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    damn... another reason to be mad at SOA! little pieces of plastic cant be that expensive... the engineering was already done, so thats no excuse! boo SOA, BOO!!!
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  15. #29
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    Its great to hear that C-West is race oriented as far as their aero kits, being how many kits out there (in general that is) are just for appearance rather than function. I had chosen the Cwest v2 kit based on the fact that it appeared functional in its design and does look great on this car.

    Some kind of plates underneath would be great, this came to my attention when I saw a GTSPEC pic with a stainless plate underneath and all their chassis bracing, I wonder if this is something thats available at retail?

    After reading this thread, Ive decided on better tires, lowering and a wing. Power and looks are great, but Id rather drive a car thats well planted and steady first.
    www.CVRMotorsports.com
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  16. #30
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    In all honesty though, I think that we are lucky with or cars with regard to aerodynamic instability...

    Try driving an Escalade at speed.... Everytime the wind blows, the whole thing drifts over a lane... very scary! On windy days, you have to be prepared to "steer into the wind" in order to keep the thing going in your own lane.
    02 WRX WRBP sedan..
    Upgrades??? stock...
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