Instability at higher speeds...
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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; About a week ago, while driving over the bridge into queens, I had her up to 60 mph and pushed ...

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    Instability at higher speeds...

    About a week ago, while driving over the bridge into queens, I had her up to 60 mph and pushed it to around 65-70 mph. It was a very windy day, when a suddenly powerful gust of wind hit the side of the car and pushed me half way into the next lane. Very alarming since this is the first time its ever happened to me in owning 8 different cars. Ive noticed the car seems unstable at any speeds higher than 60mph on a windy day, where the car is easily moved by wind.

    I searched, and the only relevant thread I found is from 02, so Im posting now to maybe determine what exactly can be done to help prevent or at least decrease the amount of instability at speeds of 60mph and higher (which I feel 60mph is WAY too low a speed to encounter instability). At the same time maybe I can learn something new and become more familiar with the wrx.

    The car is wingless, and bonestock, and the tires are bs (futura or something, came with the car), maybe these 3 have some effect, but any input is really appreciated. If Im going to mod, Id like to do it wisely and feel safer. Thanks in advance!
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    Strong winds can easily do that to any car.. It might have been just this once for you? Combination of wind and other things..

    I have never driven a wingless wrx, but my "winged" wrx feels stable in most speeds.. Feels more stable the higher speed I get.. 100-110mph it feels rock solid !! Probatly some of the stability comes from increesed downpressure from wing and liberal front grill and slightly lowered suspesion.
    Last edited by Roffa; 11-12-2004 at 02:24 AM.
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    Registered User bluerex47's Avatar
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    i have a wingless car. completely stock exterior except for the tires. i'm running on 225/45/17's and have been in triple digits and have had no problems. i've even hit those speeds on the stock re92's and everything has felt very stable. i'm sure this was a "once in a lifetime" event for you.

    if you are still worried, get wheels and tires, preferably the size i mentioned. they look great, and the added tire patch is really nice for every type of handling purpose.
    - chris
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    So the downforce that the stock wing creates would not help me? Actually no, this isnt one event. At any point on a windy day, the car is all over the place and easily moved. Ive been in weather where the wind was strong and never pushed that hard or far. Tires sound like they could be a problem though...
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    Registered User bluerex47's Avatar
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    the sti wing creates downforce, but i doubt the stocker does. i've never heard anything about it. if you are that worried, then a wing might be a better idea than tires. look at the prodrive wing (uk300) or an sti. both of those provide downforce. but then tires would help too. IMO if you have the money and want to be real safe, do both and you'll be happy.
    - chris
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    my car does that also I cant stand it. I put new tires and still hasent resolved the issue. I have been to the dealer several times to complain and they look at me like Im crazy.

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    Quote Originally Posted by bluerex47
    the sti wing creates downforce, but i doubt the stocker does.
    I think the stock wing will provide much needed downforce, not as much as the sti wing, but still...

    I forgot to say I OFCOURSE have aftermarked performance summer tires, this will also give much grip and stability..
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    it's pretty common. winds combined w/ high speeds do not mix well with the WRX. it's basically got the coefficient of drag of a cinderblock.

    upgraded suspension pretty much eliminated it all, except for some really windy days (in excess of 40mph)

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    I think stiffer suspension, and picking tires that have decently stiff sidewalls will help avoid this pretty much.

    I just switched to my snows (hakka 2's), and the car is much more susceptible to wind due to the flex in the sidewalls.

    Jay

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    The stock WRX wing is for looks. If you have seen the car in a wind tunnel you would see why. You would also see why the STI wing can actually provide some downforce.


    As for your problem, have you had the alignment checked? Maybe add some toe in?
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    I remember seeing somewhere on here a thing about WRX downforce and how the downforce is decent when the wind is straight on, but if it's coming at an angle then a lot of lift is created.

    I had noticed when I first got my car that it catches more cross wind than usual, but by now I'm used to it.. I don't even notice anymore. Suspension wise all I've got is lowering springs/good tires/performance alignment and my car feels very stable at speeds exceeding 145mph, and there's not many cars I feel safe in over 120mph.

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    Quote Originally Posted by chudlo
    The stock WRX wing is for looks. If you have seen the car in a wind tunnel you would see why. You would also see why the STI wing can actually provide some downforce.
    I have not seen the car in a windtunnel, so I rest my case. But I have feelt the diffrence of adding a 5cm front lip on a bmw.. And it made a big diffrence on sharp turns even in slow/moderate speeds. With all the wind coming down the rear window on the wrx I should thing the stock wing would give alot downforce too.. But again I have not seen the car in a wind tunnel..

    However I an relly interrested in seeing the car in a windtunnel. If anyone have vid It would be nice to see.. I have the STI wing and have often tought about how the wing creates downforce.. (If it even does) The shape of the wing would create alot downforce.. (Aircraft wing upsidedown) but the angle of it is not creating much.. So seeing it in a wind tunnel would be interesting.. (I "know" it generates DF because of shape)
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    Registered User perfusionista's Avatar
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    No wing (apart from one of those huge aero sections you see on the WRC cars) is going to give you any appreciable downforce until you get up into the 70-80mph range. And even then it's not a huge amount: I seem to remember reading that it's in the region of 35 pounds! A front lip will help more with stabilty, as it keeps the nose planted. Improving the rear and not the front will actually make it more unstable. Here on the high plains we suffer some terrible winds, it's no joke watching the hood flutter (something that doesn't usually happen until well over 100mph) at normal highway speeds! Sudden gusts from the side will make you swerve a little, but I've never gone out of the lane, and I have a wagon. Winds on bridges, however, are notorious. Sailors will tell you that there is a distinct increase in wind velocity the further you get from the surface, and so when you're several hundred feet up they can be very strong compared with what you felt before you got in the car.

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    Registered User SonicYellowWRX's Avatar
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    First of all, my 03 with stock wing had instability at speeds of over 60mph without wind. (which is actually not right and I suspect it was bad alignment or something because its been gone ever since i began modding the car and got an alignment)

    the stock WRX wing doesnt add downforce, but it reduces lift. Prodrive did a test for their Aero Pack and they tested the stock wing for a comparison.

    i did have a front lip and wing risers on at one point and they made a nice improvement.
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    Have not noticed particularly notable instability over 75mph, the WRX feels rock stable at speed compared to most of the other cars in the category that I've driven.

    The Prodrive wind tunnel date indeed showed a decrease in left generated at the rear end of the car by 30 to 35 pounds. Since lift indicates a force in the upward direction, and downforce is negative lift... a reduction of 30 pounds in lift is indeed " added downforce"; it is merely not enough downforce to overcome the lift naturally generated by the vehicle and result in a downward net force. There's nothing especially wrong with this, the stock WRX wing produces this downforce with minimal drag penalty. If you had a proper airfoil that generated say 200-300pounds of downforce, you'd be paying for it at the gas pump through the drag penalty that such a wing brings. You could get more downforce out of the stock wing by lifting it up a bit and getting it out of the boundary layer that forms due to the drop of the rear windshield, and into higher velocity air. Boundary layer phenomenon are also what the sailors are discussing. You can see this rather easily on a windy beach. Lay down flat on the sand, and you'll feel much less wind against you than if you stood up.

    Lowering the car will also improve cross-wind stability by decreasing the amount of air that gets pushed under the car. Tire sidewall stiffness will improve feel as well, as mentioned before.
    Chris Perera
    STX WRX

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