Herb Adams front spring eye brackets

Discussion in 'Suspension, Steering, Brake & Wheel Topics' started by roadrace2, Dec 18, 2017.

  1. ULTM8Z

    ULTM8Z Veteran Member

    8,462
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    May 19, 2000
    Los Angeles
    How much do these things lower the ride height?
     
  2. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    About 1/2", at least mine did

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    Last edited: Dec 23, 2017
  3. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    I can't find those gw parts anywhere.
     
  4. ULTM8Z

    ULTM8Z Veteran Member

    8,462
    101
    May 19, 2000
    Los Angeles
    Does it actually work?
     
  5. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    I did not get a chance to really find out. I took them out to buy some ground clearance.
     
  6. hquackenboss

    hquackenboss New Member

    7
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    Jan 13, 2015
    San Francisco, CA
    These absolutely work.

    Let me explain. I built the first ever version of these parts in Herb Abams' garage in 1972. I was the chassis engineer under Herb Adams on the Firebird Trans Am raced in the 1972 SCCA Trans-Am series. Herb and other Pontiac engineers taught me about increasing the percent anti-squat geometry, which Joe Brady, then of Pontiac, used on the 1964 Tempest (AKA "Gray Ghost") in the 1971 Trans-Am. I took over the chassis responsibility from Joe on the team in 1972. The Tempest used essentially a stock layout 4 link suspension with splayed upper control arms for lateral location. The implementation of the anti-squat principles is different with a leaf spring, but the physics is the same.

    Subsequent to that, Herb did extensive testing on various leaf spring cars, with the expected result that raising the location of the front leaf spring eye improved traction exiting corners (or at the drag strip).

    Anti-squat geometry, for all the articles, is not very well understood. Herb Adams' book Chassis Engineering covers it correctly, but one popular race car engineering source that flat got it wrong is the late Carroll Smith.

    Original Parts Group sells these, along with some other parts designed by Herb Adams.

    If I were going to build the ultimate Camaro/Firebird, or even Mustang live axle suspension, I would do this:
    1. Start with a leaf spring rate of ~130 to 150 lb/in. (yes. the numbers are lower than other recommendations). If you are going to have a spring built, tell the builder you want as much of the stiffness forward of the axle as possible.
    2. Use spherical bearings in the front spring eyes. (Do not use tubular bushings. Binding will occur when the car leans in a corner, causing erratic effective spring rate). Do not use urethane.
    3. Mount the axle as close to the spring as possible. Do not use lowering blocks. The further the distance between the spring and the axle, the more likely axle tramp (AKA wheel hop) under acceleration and braking.
    4. Don't use any add-on traction bars or links.
    5. If you use spherical bearings in the front eyes, you do not need a lateral locating link such as a track bar (AKA Panhard rod), or Watts linkage.
    6. Use stock rubber bushings in the rear spring eyes and at the upper attachment of the rear shackles. with spherical bearings in front, and the axle solidly mounted to the springs, the rear axle lateral location will be adequate under racing or autocross conditions.
    7. Raise the ride height by using a longer rear spring shackle. You should experiment with different heights, because there are some conflicting objectives here, so you have to find a good compromise. A lower ride has a positive effect on CG location, because the lower the better. Also, as you raise the rear of the car, the roll steer characteristics from the spring/axle geometry will change, increasing roll oversteer, which may negatively impact driver feel. However, raising the rear of the car has a positive impact on traction in a straight line or on corner exit, because it increases the percent anti-squat. Finally, about a 2 to 3 degree forward rake will be optimal for aerodynamics.
    8.Use two-way adjustable shock absorbers, and start soft. If you have axle tramp under acceleration or braking, increase the rebound shock stiffness.

    9.While you have Herb's book out, follow Herb's instructions on how to modify the rear axle for slightly negative camber, and at the same time build in a slight amount or rear toe-in using the same method described to bend the axle tubes for negative camber.

    The reason I am recommending not using any other add-on devices is that, while they may improve one thing, they may have a negative impact on another thing you want to optimize, including anti-squat and roll center location.

    Some say that the old stuff doesn't apply anymore, because the tires are completely different today. I don't buy that for a few reasons. 1) On the 1972 Trans-Am Firebird (in 1972) on race tires we measured 1.2+G on a skid pad. That's about what the best production cars (e.g. Corvette Z06, etc.) on street tires will do today. 2) While most of the 1972 Trans-Am season we raced on bias ply Goodyears, at one race where we finished second (by a few car lengths) we ran on radial Goodyear race tires. 3) My experience over the past few years with both pro-touring/Optima Challenge class cars, and studying tire models and tuning small formula cars has been they both respond to changes similar to the way race cars did in 1972. Although there have been tons of advancements, the goal of making a performance tire provide for both high lateral grip, and predictability at the limit hasn't changed. Neither have the laws of physics.
     
  7. Fbird

    Fbird Veteran Member Lifetime Gold Member

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    Feb 12, 2011
    atlanta, ga
    ;)
    i like!....difficult but like it!
     
  8. NOT A TA

    NOT A TA Veteran Member

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    Feb 12, 2009
    Delray Beach Florida
    Harry, thanks for chiming in! Since you mentioned rake for aerodynamics you might be interested in my current project. Full splitter/under tray/rear diffuser on a 70 bird. The under tray assembly along with along with a lot of other aerodynamic modifications can be seen in this 2nd gen aero thread http://transamcountry.com/community/index.php?topic=71522.0 Had a heart attack, stent operation and other medical issues that slowed me down for a while but I'm back at it! Here's a pic of the undertray design I'm working on.

    [​IMG]
     
  9. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    9,209
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    Nov 4, 2004
    Ringgold, GA
    Interesting read, thanks for the contribution Harry.
     

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