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Different approaches to reduce bumpsteer?

Discussion in 'The Hokey Ass Message Board' started by Mutt's37Buick, Apr 18, 2013.

  1. Mutt's37Buick
    Joined: Mar 28, 2011
    Posts: 174

    Mutt's37Buick
    Member

    I'm hoping some experienced builders can help me with questions I have on tie rod and center link design to minimize bumpsteer.
    I'm designing these components for my 37 Buick similar to wiki: http://www.crankshaftcoalition.com/wiki/1937-1957_Buick_Oldsmobile_Pontiac_suspension_upgrade
    I'm using primarily GM truck components in my build.
    I'm using a Saginaw gearbox instead of R&P described in the referenced wiki because I need more travel than a R&P can provide.
    One circle track website I found discusses determining a tie rod length based on geometry and then aligning that tie rod so it passes through an "instant center" (point whereupper & lower control arms cross) to reduce bump steer:
    http://www.circletrack.com/chassistech/ctrp_1001_bump_steer_explained/
    Heidts describes how the Mustang 2 front suspension works and a different expalnation for preventing bumpsteer. It says the upper & lower control arms are parallel which means there is no "instant center". It describes a specific length of tie rod that must be tied in at very specific lines.
    1) Are both methods valid?
    2) Does anyone know which approach is used in design of a 70's to 80's 2wd Chevy truck?
    Thanks
     

    Attached Files:

  2. LaSalle Gearbox
    Joined: Feb 3, 2005
    Posts: 115

    LaSalle Gearbox
    Member
    from ohio

    That circle track article does it for me.
     
  3. sedanbob
    Joined: Apr 19, 2011
    Posts: 110

    sedanbob
    Member

    Looking at the diagrams, they are both describing the same principle, having the length and pivot points of the tie rods in line with the upper and lower arm pivots, and the pivots at the spindle. They just went about describing it differently. That, and the guys that wrote the circle track article aren't trying to sell you anything.
     
  4. Mutt's37Buick
    Joined: Mar 28, 2011
    Posts: 174

    Mutt's37Buick
    Member

    Thanks for your help.
    I agree that they are similar in principle, but it seems there is one big difference.
    The circle track describes the upper control arm slanted down and a line drawn through ball joint and pivot points intersects a similar line on the lower control arm. This intersection is what they call the "instant center" and the axis of the tie rod should intersect at the same point.
    The Heidts describes the upper & lower control arms as parallel so there is no intersect point. Heidts state the inner connect of tie rod should be exactly on the plane that the upper & lower control arms fall on. I'll take some measurements on Chevy trucks & determine how they compare to these two design approaches.
    Thanks
     

  5. dreracecar
    Joined: Aug 27, 2009
    Posts: 3,151

    dreracecar
    Member
    from so-cal

    You have to remember that circle track cars are race cars that only make left hand turns whereas the Heidts is more for normal driving.

    The whole exersize here is that with both the lower control arm and short ty-rod is that you are dealing with 2 arc's. The lower CA is fixed and that arc cannot be changed. The ty-rod must be the same lenth or longer than the distance from the CA pivot to the ball joint and be paralell to the centerline of the pivot and balljoint.

    If you can find them Carrol Smith had a series of books on race car tech and one of them was on suspensions. Very easy to read and not full of tech jargon, just basic easy to understand english.

    Get youself a 3'x3' sheet of wood and some strips (yardsticks will do)
    You already know the distance of your upper and lower CA's and drill those points into the strips.
    layout the spread of the frame pivots and offset into the board and drill holes
    Figure out the distants between the upper and lower balljoint as it retains to the spindle and again drill holes. Drill another hole on the spindle strip the same distance as the spindle to reference the steering arm.
    Now make up your ty-rod strip and on one side only drill on hole and the other side drill a series of holes with the closets one being the lower CA dim.

    Now you run the suspention up and down and play with the ty-rod possision till there is none or minimal bind during travel--its as simple as that
     
  6. Mutt's37Buick
    Joined: Mar 28, 2011
    Posts: 174

    Mutt's37Buick
    Member

    Thanks very much for this detailed expalnation.
    I'll look for that book and try to lay out as you described.
     
  7. Mutt's37Buick
    Joined: Mar 28, 2011
    Posts: 174

    Mutt's37Buick
    Member

    Have an additional question on set up for reduced bump steer:
    I may be using upper & lower control arms from a 58 Pontiac on my build. Looking at pictures of this suspension, (see attached) the upper control arm appears to slant up towards the center of the vehicle. If this is the case, then did cars of this era have a different approach than modern suspensions to reduce bump steer?
    Thanks
     

    Attached Files:

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