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Thread: AE86/XE7X with RA40/60 struts bump steer 3D explanation

  1. #11
    Senior Member sr_rolla's Avatar
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    driftke70 in a corolla/ae86 moving the rack is the hard way to do it, the easy way is to use a rose joint instead of a tierod at the steering arm and space that rosejoint away from or nearer to the steering arm (look at the front end pics of the TRD sprinter in my suspension thread, you'll see what i mean)

    beerhead your part right, those drawings that you posted show that when you put the an RCA or "bump steer spacer" as you called it, you retain factory roll center characteristics and factory bump steer settings aswell. All thats being done with a RCA as driftke70 said "rca's have their place, but your not moving the control arm down when you fit them, your moving the strut up" the whole steering arm is moved away from the strut, not just the LCA or Tierod. To truly effect nothing other than bump steer you need to either raise/lower the rack or raise/ lower the tierod at the steering arm.
    Basically the idea is to get the tie rod and LCA is alignment.

    The angle of the stub axle to strut effects camber and dynamic caster, the steering arms tends to effect acerman geometry, usually as a by product of changing struts to celica or whatever.

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    Senior Member sr_rolla's Avatar
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    just thought of something else aswell, if you move the rack it would probably be a pain in the arse due to the column aswell, just a thought

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    Cheers guys, that makes some sense, I like informative posts where I learn something new.

    Honestly, I don't think many people have actually realised having steering arm in the wrong plane can have such an adverse effect on handling, even if you don't think it's "Bump steer". It'll cause a wheel to toe in and out, and I don't know another word more fitting to describe the effect.

    I know that exactly what a kingpin is. But you don't know that the kingpin angle is exactly what I said it is. It's the angle of difference between the wheel and the strut, and that is dictated by the stub axle. 90 degree + the kingpin angle = stub axle angle.




    Honestly ant, it's not what you say, its how you say it, if you want to show you're Omega 1 suspension guru master, can you actually explain things in decent manner.

    <div class='quotetop'>QUOTE (Anthony @ Sep 1 2008, 12:00 PM) </div>

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    Senior Member sr_rolla's Avatar
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    Are you talking about the toe changing as u steer? as in, the more lock you wind in the more toe in/out you'll have?

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    Veteran driftke70's Avatar
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    or toe out on turns, which again leads to ackermans,

    the king ping angle isnt so much as relevant as the king pin inclination,

    castor effects toe on turns slightly, depending on how much you run,

    also it is relevant to the suspension you run, if you are speaking about a car with say 8 or 9 kg springs where the front is never really taking much a of a stroke, the bump steer effect doesn't really occur, if your car is set up properly, suspension wise, you should be able to drive through bump steer easily.
    wheelfriends.wordpress.com

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    Senior Member Ksevn-T's Avatar
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    Theres a few little bits and pieces worth adjusting as the other guys have picked out but the drawings are Impressive!!!
    数独のガレージ "Sudoku Garage" <3<3<3

  7. #17
    Junior Member streets's Avatar
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    Just finished reading this thread, nice drawings by the way; and thought I'd add my 2c (in case anyone cares).
    Beerhead is actually correct in suggesting that changing the control arm/tie rod angle in a corolla/sprinter affects the bumpsteer characteristics (or increased toeing during suspension movement to be specific), and the reason is this...
    The rack end and contol arm are not perfecty parallel, nor do they pivot from the same position. Hence; if you have the supspension lowered away from the 'ideal' factory relationship, the toeing affect of the suspension movement is exaggerated as the components move further from parallel.
    And here lies the advantage of the bolted on steering arms and control arms in the toyotas, as a simple bolt on RCA can restore the components to roughly their factory positions. The xE7 and AE8 chassis however are certainly not extreme examples, as lowering will not result in dramatic increases in bump steer (as shown in beeerheads first pic); however, fitting different struts with changes in strut length and KPI can certainly have adverse affects.

    Hope that makes sense.

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    Senior Member sr_rolla's Avatar
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    yes, but all fitting an RCA does is restore the factory bump settings, if you wish to dial out only the bump, u need 2 move the tie rod in relation to the steering arm to bring them back to parallel (generally done by either moving the rack as driftke70 said or modify the tie rod ends as i desribed)

    What i get from beerheads 1st post is that he is saying that puting celica struts into a ae/ke will cause bump steer, it wont, it will however, stuff up kpi and ackerman angles.

  9. #19
    Junior Member streets's Avatar
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    Fair nuff.
    It should be mentioned though, that fitting RCA's is still crucial on a lowered car, even if the tie rods/rack are repostioned. I say this as even in a sensibly lowered 86, the control arms will sit close to or beyond horizontal, meaning that as the outside wheel is weighted during cornering; the control arm movement results in a reduction in negative camber, possibly going past zero into postitive territory. :hammer:

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    <div class='quotetop'>QUOTE (driftke70 @ Sep 1 2008, 07:26 PM) </div>If you where moving the strut up, RCA's would change the ride height, but they don't.

    They move the arm down and bring the roll centre closer to that of stock.

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