modified knuckles

Discussion in 'Drift Racing Tech Discussion' started by Dallas The-Awsome, Feb 27, 2014.

  1. Dallas The-Awsome

    Dallas The-Awsome Junior Member

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    I was wondering if anyone wants to share there specs on there modified knuckles like the fabrication specs
     
  2. Ike

    Ike forum member

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    While I don't know the fab specs for mustangs specifically, I do know what you want mathematically and ideally from a physics and suspension geometry point of view.

    1. The steering rack and it's tie rods should be colinear (in a straight line with) with the pickup points on both knuckles.

    So if the wheels are straight ahead, with the car resting on the ground, you should be able to draw a straight line from the center of the outermost ball joint where its attached to one knuckle, through the center of the tie rod, rack, other tie rod, and center of other ball joint on the other side. Everything.

    2. The inner pivot of the tie rod on each side to be colinear with the a-arm pickup points (bushings)

    This means a straight line through both a arm bushings where they attach to the chassis, and straight through the inner tie rod joint.

    3. The hard one: The outer pivot of the tie rod on each side should be parallel to the a arm's geometrical location.

    If the a-arm wasn't a-shaped and was just one bar from its pivot (or its instananeous pivot in the case of the future s550 mustang) extending down perpendicular to its rotational axis (axis made by chassis pickup bushings) then the tie rod should be parallel to this.

    The reason I cant, like in number 2, simply say that the outer tie rod pivot should be colinear to an axis extending directly rearward from the lower ball joint, which would be nice, is that all cars have some degree of built-in positive ackerman, and this ackerman means the outer tie rod pivot is set inward a certain number of degrees on an imaginary circle as drawn from a perspective overlooking the car and radiating from the ball joint.

    With this in mind, engineering some bump steer and other crap into the car is usually done by offsetting the rack position, and so 1 and 2 might not work either, and bump steer is great for lawyers at a major OEM because too fast straight off the road is usually attributed to driver error, whereas too fast backwards off the road is more likely to become attributed to the fault of the OEM, even if the same car, same speed, and same circumstances contribute, while in reality the built-in understeer is meaning the car will go off the road at an overall slower speed, it means onlookers can blame the driver, as opposed to the spinning car, which means onlookers blame the OEM.

    Ackerman is built in to keep tires from scrubbing, while at high G, pneumatic trail comes into effect due to tire deformation, and you'll surely recognize negative ackerman if you watch F1 cars' front tires while they turn. Negative ackerman can be utilized for road racing, but positive ackerman is good of drift because it means the more you turn, the more you understeer. This allows pretty good oversteer in at low steering angles, while with a little more correction, this positive ackerman, which is understeer-y under high-G due to pneumatic trail, helps you get out of the drift.

    -----Layman's terms-------
    Or how your average drifter is going to do it..............

    Take off your springs, keep shock on
    raise tire to highest point in travel, damper against it's bumpstop
    turn steering wheel all the way toward side you're measuring on (right tire, turn to right)
    take off tie rod
    cross tie rod over little arm on spindle that it bolts to
    viewed overhead, this makes an X with the tie rod and the little arm on the spindle
    move them inward together, so legs of the X get bigger, and tire becomes turned more
    when wheel lip hits a arm, back off a bit
    mark where tie rod is crossing the little arm that holds it to the spindle
    if its 1 inch, for example, from its original position, then cut one inch out of middle of little arm
    weld attachment point back onto spindle with one inch missing
    remember to do this with suspension compressed, because there is less clearance between wheel and a arm with suspension compressed.

    I take no responsibility for you messing up your car.
     
    Last edited: Mar 13, 2014
  3. Ike

    Ike forum member

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    If you can interpret that I'll be impressed, otherwise let me know and I'll make pictures in CAD
     
  4. C.Love

    C.Love forum member

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    The s197 chassis is alot easier than the old mustang chassis. I personally would send them in have derrick modify them for iirc 200 bucks and be done with it. There is a ton of theory but in the end theory is just that. Do what works
     
  5. Ike

    Ike forum member

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    Yes, Derrick R. is who I am planning to send mine into. Answer to a different question but probably the answer you wanted. Few hundred bucks IIRC.
     
  6. C.Love

    C.Love forum member

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    Basically what he wanted is to know you cut the knuckle where and weld it back to where. Its not that easy and my theory comment was because most guys just trial and error several sets of knuckles until they find what works. Case in point, I had a few knuckles on my 240 in my day and one set from a major company was complete shit and the other a complete dream. I can almost gurantee you neither company looked at a dynamics book and played by the proverbial rules. The theory is good to know but in practice its just theory. You can pick up a book on suspension dynamics and go through theory and the inner working of suspension bits. In the end what is theory really? Its an idea that on paper should work.

    My attention span the last few weeks is too little to read what you typed but I am looking forward to reviewing it some time soon (school has by brain space right now lol)

    Personally I am trying to offload my mustang in favor of something a bit better (and cheaper) for drifting.
     
  7. Dallas The-Awsome

    Dallas The-Awsome Junior Member

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    i got mine done local not the most angle but it means no international shipping to send them to derrick