Teh Cone Dodgin' STX Wagon - Page 6
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This is a discussion on Teh Cone Dodgin' STX Wagon within the Motorsports Talk forums, part of the Community - Meet other Enthusiasts category; I'll think I'll keep to my masters in Business cheers, but obviously if you would bless us with your knowledge ...

  1. #76
    Registered User Oak1ey's Avatar
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    I'll think I'll keep to my masters in Business cheers, but obviously if you would bless us with your knowledge I would be honoured !!

    However being that clever do you really need Excel
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  3. #77
    Registered User Oak1ey's Avatar
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    All joking aside anything like that would be wicked, I have a fairly good understanding of cars but when you are talking geometrics (if you have electrical adjusted suspension ) I would be happy with any help.

    PS. By the way nice to me yer
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  4. #78
    Registered User Oak1ey's Avatar
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    I meant nice to meet yer !!
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  5. #79
    Moderating on the run! Big Sky WRX's Avatar
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    bump for the spreadsheet
    "Simplify and add lightness." - Colin Chapman

  6. #80
    Registered User wrx wagone's Avatar
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    Quote Originally Posted by Oak1ey View Post
    I meant nice to meet yer !!
    Yeah, you too. Stay tuned to the thread. Lot's of notes to come.

    Quote Originally Posted by Big Sky WRX View Post
    bump for the spreadsheet
    Ok!

    Now, here's the deal with this spread sheet...

    These numbers assume the following:
    1. The "arms" of the swaybar do not have any deflection.
    2. That the spring rate is linear, it is in fact not as the position of the endlink relative to the "arm" of the swaybar changes during the movement of the suspension, which changes the direction of the force vector acting on the swaybar.
    3. The measurements of the length of the "arm" are very critical to these numbers enough so, that I currently don't "completely" trust my measurements, but this information (notice I didn't call it "data") paints a very useful picture.

    Use this spreadsheet to help with getting a feel for the order of magnitude of a swaybar change.

    Ok, so I can't attach an excel file, but shoot me a PM and I'll email it to you if you would like it.

    I will post the entertaining graphs as images.
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  7. #81
    Registered User wrx wagone's Avatar
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    Alright so, this first graph shows the effect of changing only the diameter of the swaybar while all else (arm length, overall length of the bar itself) remains unchanged.



    You can clearly see that this is an exponential function, in this case a fourth order exponential function.

    Changing the diameter of the bar will have a pretty large effect on your roll stiffness. Stands up with realistic data.


    This graph shows the effect of changing only the length of the "arm" of the swaybar, ie. changing holes on an adjustable bar. I used a 22mm bar diameter to produce this graph.



    Again this is also an exponential function, albeit an inverse second order one. This shows that very large changes in bar stiffness can be had by dropping endlinks in different holes..

    Note: Ray has probably lost his load about now...

    So overall, these graphs should paint a pretty good picture as to the order of change these basic adjustments to your swaybars should make.

    Happy motoring!
    Last edited by wrx wagone; 05-12-2008 at 10:18 PM.
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  8. #82
    Moderating on the run! Big Sky WRX's Avatar
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    interesting- this does a good job of pointing out that while making a substantial change in spring rates say 200->400 obviously changes roll resistance fairly substantially, that changing sway bars could have a far greater impact

    looks like your numbers are roughly in line w/ Stretches
    "Simplify and add lightness." - Colin Chapman

  9. #83
    Registered User wrx wagone's Avatar
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    Quote Originally Posted by Big Sky WRX View Post
    interesting- this does a good job of pointing out that while making a substantial change in spring rates say 200->400 obviously changes roll resistance fairly substantially, that changing sway bars could have a far greater impact

    looks like your numbers are roughly in line w/ Stretches
    That first comment is exactly right, and this also goes back to one of my setup theories.

    The springs on the car will control both pitch and roll, they are also the only suspension part that controls pitch, so you need to set your springs to give you the pitch control you need and then balance the roll stiffness back with swaybars, which obviously can have a much greater effect on roll stiffness than springs.

    I also noted that my numbers are fairly close to stretches' numbers (probably used the same engineering). The variation can easy be caused by some variation in the measurement of the arm length of the swaybar.
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  10. #84
    Moderating on the run! Big Sky WRX's Avatar
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    there is an ongoing "argument" amongst road racers and even NASCAR folks on chassis setup w/ "softly" sprung/big sway bars vs "heavily" sprung/smaller sway bars

    still comes down to real world testing (and a lot to do w/ driver's preference)- that's where threads like these definitely help out
    "Simplify and add lightness." - Colin Chapman

  11. #85
    Registered User wrx wagone's Avatar
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    Something else I was thinking about with this swaybar discussion is that the swaybar endlinks attach much closer to the pivot point then the struts which then means that the control arm is able to apply more force into the swaybar as compared to the springs.

    So... these numbers are merely informative not actual realistic data.
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  12. #86
    Moderating on the run! Big Sky WRX's Avatar
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    Quote Originally Posted by wrx wagone View Post
    Ok!

    Now, here's the deal with this spread sheet...

    These numbers assume the following:
    1. The "arms" of the swaybar do not have any deflection.
    2. That the spring rate is linear, it is in fact not as the position of the endlink relative to the "arm" of the swaybar changes during the movement of the suspension, which changes the direction of the force vector acting on the swaybar.
    3. The measurements of the length of the "arm" are very critical to these numbers enough so, that I currently don't "completely" trust my measurements, but this information (notice I didn't call it "data") paints a very useful picture.


    .
    couple of question if I might

    to #1 lets say that there is some deflection of the "arms"- I assume that move the rates downward?

    to #2, if the rate is more progressive vs linear, would that also move the rates downward?

    I guess my premise for asking is while I realize that the sway bars play a significant role in roll stiffness, I still find the numbers higher than what I think they should be
    "Simplify and add lightness." - Colin Chapman

  13. #87
    Registered User wrx wagone's Avatar
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    Quote Originally Posted by Big Sky WRX View Post
    couple of question if I might

    to #1 lets say that there is some deflection of the "arms"- I assume that move the rates downward?

    to #2, if the rate is more progressive vs linear, would that also move the rates downward?

    I guess my premise for asking is while I realize that the sway bars play a significant role in roll stiffness, I still find the numbers higher than what I think they should be
    #1 Yes, but I just did some napkin math and the "arm" would deflect somewhere on the order of 0.0006" or less. This works out to ~1lb or less. This is negligible.

    #2 Actually according to my napkin math, the value actually increases 2% or ~10-30 lbs. Again, negligible.


    I think the real truth here lies with the relationship of where the strut and the endlinks mount to the control arm. If the endlink mounts apporximately half way between the ball joint and the pivot of the control arm, then when the end of the control travels 1" the endlink travels 0.5".

    So, if you have 500 lb/in springs it just took 500 lb force to move the control arm 1", and if you have a 1600 lb/in swaybar, it took 800 lb force to deflect the swaybar through that same motion.

    Edit: Well, I'm giving this even more thought and to calculate these swaybar spring rate values I assumed that the other end of the swaybar was being held fixed, however a 0.5" defection upward should also cause a 0.5" deflection downward on the opposite control arm. So, all in all I'd say that these numbers are fairly accurate, assuming my measurement of the swaybar "arm" is reasonable. This is probably the largest source of potential error.

    Also I compared my roll numbers from last year's bar and springs to this year's bar and springs and the numbers are very close for a similar amount of roll.
    Last edited by wrx wagone; 05-14-2008 at 10:31 PM.
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  14. #88
    Moderating on the run! Big Sky WRX's Avatar
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    how are you measuring roll?

    what would be very interesting to do to prove this out would be to run a stock WRX around some corners and measure roll and then remove the sway bars f/r and put on 600# ish springs (the ballpark equivalent of oe springs and 20mm swaybars) and measure roll again
    "Simplify and add lightness." - Colin Chapman

  15. #89
    Registered User wrx wagone's Avatar
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    Quote Originally Posted by Big Sky WRX View Post
    how are you measuring roll?
    My highly accurate perceptions on course.
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  16. #90
    Moderating on the run! Big Sky WRX's Avatar
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    Quote Originally Posted by wrx wagone View Post
    My highly accurate perceptions on course.
    gotcha

    what I was thinking on the "experiment" would be something along the lines of choosing several different corners and photograph the car as it goes through- the angle of the front (and/or rear) bumper could be compared to the other setup
    "Simplify and add lightness." - Colin Chapman

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