Swaybars

Discussion in 'Suspension and Chassis' started by 03dakrt, May 28, 2018.

  1. 03dakrt

    03dakrt TMO Intermediate

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    Hi

    Need advice on sway bars

    Trying to decide if I should change the stock gt brembo bars for aftermarket
    Car has bmr track springs, koni yellow, upper and lower control arm for rear and a few other small suspension items. I autocross and OTD the car plus out a few thousand miles per summer. Car is easy to drive fast now and don't want to loose this.

    Thoughts?
     
  2. Mad Hatter

    Mad Hatter Gotta go Faster

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    I would start with a adjustable front bar first, and always tires!!
     
  3. Grant 302

    Grant 302 OPM Spent: $665,833 Moderator

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    Unless there's some specific reason to change either bar, I'd say, 'no'.

    More details on your setup or any issues or something you'd like to improve might help.
     
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  4. Norm Peterson

    Norm Peterson Corner Barstool Sitter

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    What Grant said.

    Is there something about the way the car drives at this stage that you think it could/should be doing better? Anything it does that you think it shouldn't?

    Given your last sentence, if/when you do swap the OE bars out for something from the aftermarket you might want both bars to be adjustable.

    Out of curiosity, which BMR springs are those "track springs"? BMR has some "GT Handling Springs", and at least used to have a separate set of "Handling Springs" specifically for the GT500 that were about 20 lb/in stiffer.


    On edit, I also went through your "Oversteer" thread, where the matter of tire size came up. Have you changed that situation yet? FWIW, 285/35's seem to be at least adequate for the 4.6L power level if driven smoothly - I'm somewhat less sure about their appropriateness at higher power levels with more of a point-and-shoot driving style.


    Norm
     
    Last edited: May 29, 2018
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  5. 03dakrt

    03dakrt TMO Intermediate

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    I would assume handling would improve as you would be able to keep more tire on the pavement. Based on responses seems like i should save my money.
     
  6. 03dakrt

    03dakrt TMO Intermediate

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    Correct handling spring.

    No tires aren't done yet and will go larger next time.
     
  7. Norm Peterson

    Norm Peterson Corner Barstool Sitter

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    There's more than one thing going on here. On the one hand, lower amounts of roll result in smaller amounts of (negative) camber loss. But on the other, the front vs rear balance of lateral load transfer can easily be altered, resulting in a steady-state handling balance that could be more understeerish, closer to neutral, or all the way into oversteerish. Note that 'perfectly neutral' might not always be the hot tip, and that it's even possible in some cars to gain total cornering grip and get slightly heavier understeer at the same time.

    My take is that changes in understeer/oversteer handling balance show up long before you'll notice any significant reduction in roll.


    Norm
     
  8. Mad Hatter

    Mad Hatter Gotta go Faster

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    TIRES!! Big fat tires!!!
     
  9. twistedneck

    twistedneck TMO Race

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    Bars can contribute up to 70% of the roll rate on very sodtly sprung trucks.. less on softly sprung cars. Race cars have only 10-20% cause u dknt want to pick up the inside wheels too much.
     
  10. Norm Peterson

    Norm Peterson Corner Barstool Sitter

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    I suspect most street-driven cars with both "lowering springs" and aftermarket sta-bars are somewhere around 65% bar. I'm getting about 63.5% bar for the car in my sig on Strano bars (mid settings) and BMR's GT500 Handling springs.

    One problem with 10-20% bar in a dual-purpose car is that you might not be able to live with the ride quality on the street.


    There is also the big bar/soft spring philosophy, perhaps most closely associated with NASCAR where high speed aero considerations can override other reasons. Let the nose dive to keep air from getting underneath, but don't let it roll and grind the right side/lift the left and let too much air get underneath anyway.


    Norm
     
  11. Grant 302

    Grant 302 OPM Spent: $665,833 Moderator

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    I've been meaning to 'cover' part of this topic. 'Roll rate' and outright 'spring rate' of a sway bar are very different...especially when comparing percentage to spring/wheel rates.
     
  12. Norm Peterson

    Norm Peterson Corner Barstool Sitter

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    Agreed.

    In developing a TLLTD spreadsheet the results I got made a lot more sense once I reflected bar end stiffnesses back to the chassis mounts and developed the moment from those and a rotation from the end deflections. Reflecting bar rates in lbs/in out to "spring rates" at the wheels kept giving unreasonably low roll/g results.


    Norm
     

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