Instability at higher speeds... - Page 3
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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; I need to get my hands one thoose JDM undercar stuff.. And make a replica in CF/kevlar so it can ...

  1. #31
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    I need to get my hands one thoose JDM undercar stuff.. And make a replica in CF/kevlar so it can take the beating of rocks and ice

    Aerodynamics are complicated and I know subaru have spent much money and time in windtunnels to get it right... Therefore I'm afraid to "**** up" what subaru have done with some stupid aftermarked kit.

    Take a look to the Audi TT, after a highspeed accident (The car was taking flying lessons)Audi recalled some of the early TT's and added at tiny spoiler on the back... It made all the diffrence...

    My goal would be to have a complete protection under my car to fight rocks and ice while weekend rallying, while not ruin aerodynamics. Prefarable make more downforce so I can safer enjoy speed like 160mph...

    To bring back the other part I was haveing questions about rear diffusors.
    For looks only or does it have a positive effect?

    Any windtunnel pics /vids of wrx/sti would be really interesting to see..

    Btw my rex is lowered and with aftermarked tires and I have never had any experience with instabillity in any speeds.
    Last edited by Roffa; 11-26-2004 at 06:17 AM.
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  3. #32
    Moderating on the run! Big Sky WRX's Avatar
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    Someone suggesteed to me that the 05 (USDM) STi might have some of this cladding as oem, if anyone has a 05 thye could kindly climb under and see?

    If not I'll be at the dealership within a couple of weeks and see. If they do, the next question would be if we have the places to bolt up the cladding- fingers crossed.

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  4. #33
    Registered User SonicYellowWRX's Avatar
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    you know, i hear of guys in japan and the uk doing insane speeds while reporting no wind noise and great stability and i had no clue as to why...now i know the underbody aero cladding is why! i would like to get my hands on a set...

    anyways, i am not familiar with race diffusors as I have never actually seen one cuz its underneath the car. i do know its a lot more complicated than the oem piece. basically from what info i can find on F1 cars, its job is to create a low pressure area behind the car and to control and smooth out the airflow to maximize this effect. I guess this further improves the suction effect by further speeding up the airflow. (high pressure moves to low pressure; I learned that in some science class in high school or college ) here's a link that explains the diffuser and has a little picture of a "simple diffuser": http://www.scarbsf1.com/diffuser.html
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  5. #34
    Moderator schischwein's Avatar
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    Quote Originally Posted by SonicYellowWRX
    you know, i hear of guys in japan and the uk doing insane speeds while reporting no wind noise and great stability and i had no clue as to why...now i know the underbody aero cladding is why! i would like to get my hands on a set...

    anyways, i am not familiar with race diffusors as I have never actually seen one cuz its underneath the car. i do know its a lot more complicated than the oem piece. basically from what info i can find on F1 cars, its job is to create a low pressure area behind the car and to control and smooth out the airflow to maximize this effect. I guess this further improves the suction effect by further speeding up the airflow. (high pressure moves to low pressure; I learned that in some science class in high school or college ) here's a link that explains the diffuser and has a little picture of a "simple diffuser": http://www.scarbsf1.com/diffuser.html
    If any of you don't understand what Sonic is reinterpreting...yet another leyman's way is to think of what expansion chambers do for a two-stroker
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    Quote Originally Posted by SonicYellowWRX
    you know, i hear of guys in japan and the uk doing insane speeds while reporting no wind noise and great stability and i had no clue as to why...now i know the underbody aero cladding is why! i would like to get my hands on a set...
    What underbody stuff does the USDM version come with?
    My EDM WRX are just missing the two plates on each side...

    Anyone know who sells "rally spec" under car protection plates? Perferable CF/kevlar to keep the weight down..
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  7. #36
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    USDM, we have a little plastic shield up front i ripped off to replace with a skidplate. The skidplate is much bigger and probably does more aerodynamically than that thing did.

    As for kevlar underbody protection, these guys have it on their site... http://www.rhrperformance.com/ Its not too cheap though. (and kevlar gets torn up eventually and you have to replace it.) It doesn't look to be any different aerodynamically though.
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  8. #37
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    Quote Originally Posted by thechickencow
    I think stiffer suspension,
    Jay

    stiffer springs.. that's about all u need. once i got my v7 sti suspension on my 03 wrx it eliminated the "floaty" feeling I used to get at high speeds.
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  9. #38
    Moderator schischwein's Avatar
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    Quote Originally Posted by Roffa
    What underbody stuff does the USDM version come with?
    My EDM WRX are just missing the two plates on each side...

    Anyone know who sells "rally spec" under car protection plates? Perferable CF/kevlar to keep the weight down..
    There are plenty of different kind of materials for rally protection....mainly it comes in various type of plastic or rubber/urethane sheets....CF could be very expense for rock, gravel, sand blast protection....It takes long to install however as if requires riveting the sheets to the underbody all over. For it to be of any use aerodynamically, it should be hard as fluttering sheets would disturb flow. It would be interesting to look for semi-porous/crater sheets however...microcirculation on the surface can lower the fluid friction.
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  10. #39
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    Quote Originally Posted by schischwein
    It would be interesting to look for semi-porous/crater sheets however...microcirculation on the surface can lower the fluid friction.
    like the dimples on a golf ball.

    Lexus actually did that on their flagship LS430 sedans to further reduce resistance and wind noise.
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  11. #40
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    Quote Originally Posted by SonicYellowWRX
    like the dimples on a golf ball.

    Lexus actually did that on their flagship LS430 sedans to further reduce resistance and wind noise.
    Yes they did.........and so did Carrera on my old skiracing helmet

    But yes....dimples like a golf ball
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  12. #41
    Moderating on the run! Big Sky WRX's Avatar
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    Quote Originally Posted by Roffa
    What underbody stuff does the USDM version come with?
    My EDM WRX are just missing the two plates on each side...

    Anyone know who sells "rally spec" under car protection plates? Perferable CF/kevlar to keep the weight down..
    Here's some nice undercarriage protection:

    http://www.umsrally.com/e_OriginalParts.htm

    I've just confirmed the USDM 05 STi comes w/ the rear cladding as pictured- it doesn't offer nearly as "complete" as a front undertray as pictured- I believe it is the same as the 04/05 WRX tray.

    I'll try and figure out if the aero bits can be retrofitted
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  13. #42
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    I had a problem like this in my '09 WRX. I was crusing at about 80mph, everything feeling stable, then I passed an 18 wheeler who was doing 70. It was an 18 wheeler without any aero on it so the wind around it was all over the place, all confused.
    My car suddenly felt very unstable like it was going to go flying, lighter steering, washing side to side. Once past that area it was back to normal.
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  14. #43
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    Quote Originally Posted by jharry3 View Post
    I had a problem like this in my '09 WRX. I was crusing at about 80mph, everything feeling stable, then I passed an 18 wheeler who was doing 70. It was an 18 wheeler without any aero on it so the wind around it was all over the place, all confused.
    My car suddenly felt very unstable like it was going to go flying, lighter steering, washing side to side. Once past that area it was back to normal.
    Interesting first post..... Why did you dredge up an 8 year old topic to respond to that talks about a totally normal aspect of physics which is that high winds affect large objects?

    Anyhow welcome to the forum...
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  15. #44
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    Quote Originally Posted by jharry3 View Post
    I had a problem like this in my '09 WRX. I was crusing at about 80mph, everything feeling stable, then I passed an 18 wheeler who was doing 70. It was an 18 wheeler without any aero on it so the wind around it was all over the place, all confused.
    My car suddenly felt very unstable like it was going to go flying, lighter steering, washing side to side. Once past that area it was back to normal.
    Awesome 8 year post bump!

    Least it shows newbs are using the search button!!!

    Odd though, cause I've passed numerous semis without any problem like that at speeds anywhere of 70-90mph. I've never felt any instability. Must be the park bench.
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  16. #45
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