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    steering rack pivot points
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    Im designing my front suspension and steering, I have been reading up about geometry and bump steer which I want to minimise as much as possible.I am using a cardboard model to figure out where I should position everything so it all lines up to the instant centre.The problem I have is the steering rack I have is about 160mm wider than the front frame of the buggy so unless I make a frame to mount the a arms further out (which I dont think it would look right and im cincerned about strength) then I think this rack is gonna be no good.I have been wondering is there another way round it? Can I move the rack further forwards or backwards to help compensate for this?
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    Re: steering rack pivot points
    #2
    The Bob Ross of MBN Bullnerd's Avatar
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    Frame is done already?

    Are you taking Ackerman into account? That will move the steering arms out a bit at the spindle.

    Rack pivots wider than the arm pivots at the frame is usually ok.
    "Speed is time-time is speed"-Dennis Hopper

    Quote Originally Posted by TALON View Post
    did you use a special bigfoot camera or something ,you know all blurry could be a tree stump kinda thing .
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    Re: steering rack pivot points
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    I bought a single seat frame that I am only extending at the front, I am thinking about ackermen, the steering knuckles have removable brackets where the track rod end bolts to.I am going to try to mount the a arms in the right place for zero ackerman but if it cant be done I will have the brackets re manufactured, I may do this anyway as I want decent steering lock (I have come from drifting).My main concern is that one suspension diagrams I have seen(im not able to upload pics from my phone) if you have an imaginary line extending the a arms and tie rod, they should meet at the instant centre, this is fine but then there should be another almost vertical line connecting all 3 pivots, with the rack I have this isnt going to work.Or am I missing something really obvious here?
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    Re: steering rack pivot points
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    Millenium Member Xbird's Avatar
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    no, you are on the right track. if you haven't fixed in on the rack's mounting height, you can make a spreader-like drop link that attaches to either end of the rack so you can move the tie rod mounts below the rack and inboard of the ends if you need a narrower connection spread. my setup isn't ideal, (have some bump steer) but it has a drop link i made for close to the same reason.
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    Re: steering rack pivot points
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    The Bob Ross of MBN Bullnerd's Avatar
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    "vertical line connecting all 3 pivots"

    This is not necessarily true and probably not in more cases than it is.

    The inner pivot is a function of the arc the outer tie rod point travels through. Find the center of the arc and you have a very good starting point for the pivot location.

    You can easily do this with the cardboard you mentioned.

    Would really help if you could post pics.

    Where are you located?
    "Speed is time-time is speed"-Dennis Hopper

    Quote Originally Posted by TALON View Post
    did you use a special bigfoot camera or something ,you know all blurry could be a tree stump kinda thing .
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    Re: steering rack pivot points
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    Cheers guys, xbird do you have any pics of how this is done?Bullnerd, I dont mean exactly vertical but that was just to explain it, I am learning alot about suspension geometry, not sure if I am over thinking it really, I think I am going to work it out as close as I can but then make sure I have adjustment in lots of areas.Im in the uk, also should have said this is mainly going to be used for on road.Will work on posting pics which I will put on a project thread when I can.
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    Re: steering rack pivot points
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    Millenium Member Xbird's Avatar
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    steinfr.jpg I made this spreader type piece about 7 years ago after i pulled the bonehead move of setting up the rack mount for the rack in an upside down position. It's going to take some major chopping to set it to the correct height, this winter i may finally get to putting a new one in correctly since this rack is beyond worn out. Its essentially two pieces of square tube that fit one inside the other with flat stock welded to each tube and a round cap with a bolt hole welded in between the flat stock. the two halves slide into each other and bolt through the round cap into the rack ends. a shallow head thru-bolt then goes through the square tube. About the only picture i could find, most of my old build pics are in a hard drive from my old XP computer. Do NOT go by the tie rod connection locations, neither end is quite correct, I used golf kart hubs that caused me no end of interference issues for what I was trying to get travel wise, i do have toe in on bump.
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    Re: steering rack pivot points
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    Ok, looking at this and others I think I need to go for a shorter rack and extend it, im just in the process of mocking up front suspension and seeing what clearance I have
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    Re: steering rack pivot points
    #9
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    I had a write up and some drawings, pics lost in site swap a couple yrs back.

    So; front or rear steer spindles?
    Looking dead straight at spindle, draw a line from upper arm mount and lower mount.
    Then a pararell line thru tierod mount.
    Measure distance between 2(write down)
    Move to inner arm mount,
    draw line from top arm thru lower arm mount.
    That number (write down one) that's how far the tie rod mount needs to be inside or outside of line.


    Now if outter tierod mount is say 60% up/down measurement of outter arm mount inside needs to be same %. Not same 2 or 3"" number as inside verticle measurement should be less to get proper camber gain.


    Looking from overhead, should be a straingt line from spindle to other.
    Once you have all these spots you now know whered the rack should be placed, front-back in car, and up-down. And how wide the rack should be. And you be lucky to find a rack that size, unless you build the car to fit a rack. A center mount rack with a custom spreader bar can be easier.


    This is perfect world, most of our stuff is not perfect, so some compromise comes into play.
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