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Thread: The Suspension Setup Thread

  1. #61
    Senior Member sr_rolla's Avatar
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    (quote old thread simon ae86)

    this is the reason in my choice of using the nissan crossmember and rack, all pivot points should be the way that nissan designed them, in theory anyway.

    KE70dave: interesting to see you used stock length arms, you didnt find them too long and cause massive camber? Or did you slot the top bolt hole on the coilover strut to reduce camber?

  2. #62
    Senior Member sr_rolla's Avatar
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    (quote old thread ke70dave)

    nah seems to be ok, but I'm using pretty "crap" offset wheels (in ke70 and ae86 terms) as stated they are 15x6.5 +23 with 195/50's

    this is with the camber top on full negative (-3 deg), and i havent modded the top holes at all, standard placement.

    i don't have a pic of it now (with -2 degrees) but its pretty much flush with guard (those stocko ke70 guards in the picture are essentially untouched)

    i would like to get shorter ones, but better things to spend money on/worry about for the moment

  3. #63
    Senior Member sr_rolla's Avatar
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    (quote old thread ke70dave)

    ok i have results

    at the crossmember end it was found that where the LCA bolt and where the steering arm joints the steering rack (right at the ball joint) is essentially in EXACTLY aligned.

    i did this by putting a screwdriver in line with the LCA bolt and lined it up with the ball joint in the rack end, and the screwdriver was essentially parallel.

    also i figured this end wasnt as important because its the same setup that is used with ae86 stuff anyway (Same LCA bolt position, and same steering rack position)

    now onto the other end.....

    here is a diagram i drew up in solid edge, its 1:1 scale so its all exact. also note i took these measurements with weight on the front wheel, i put some bricks under the control arm and let down the jack to get as close as i could to static position.

    also the measurements of the ball joint were taken at the pivot point of the ball joint (or close too..since you can't actually see it)

    Click image for larger version. 

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    now as can be seen, the steering arm is 30mm shorter than the LCA, and the steering arm sits up 10mm higher than the LCA at the brake disc end.

    now i have nothing to compare to, but how bad is this in terms of "bump steer"??

    just thought id post my results anyway...

  4. #64
    Senior Member sr_rolla's Avatar
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    (quote old thread simon ae86)

    the more crossed up those two arms get the more pronounced the bump steer effect, when i fitted my susp up, i had a horrible angle on the tie rod, since the S14 rack is a lot lower then KE, so the start of the tie rod was a lot lower then the ball joint end where it bolts to the steering arm, I temporarily fixed mine by using bump steer adjusters on the toe arm, dropping the arm about 50-60mm lower from the steering arm.

  5. #65
    Senior Member sr_rolla's Avatar
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    (quote old thread ke70dave)

    ok i have my own answer

    after doin a bit of thinking, and mucking around in this program, i have come up with the following results

    considering 2 scenarios

    the first scenario is with a suspension compression of 50mm (a fair way with 8kg springs, but certainly obtainable) it sias 49.5mm but close enough

    here is the geometry:

    Click image for larger version. 

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    now as can be seen, as the control arm is moved up 50mm, the pivot point at the ball joint moves 3.52mm, where as the steering arm moves in 4.64mm, resulting in a toe out
    change of 1.12mm (considering only one front wheel, assuming the other wheel does not get effected by this suspension compression)

    now the next scenario, is a worst case scenario, where the suspension is compressed 100mm (this would be a pretty psycho bump, and woudl result in worse things than bump steer...namely bottoming out...but neverthe less...)

    here is the geometry for a 100mm compression:

    Click image for larger version. 

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    as can be seen from this diagram, for a suspension compression of 100mm, the control arm moves towards chassis by 14.59mm, where as the steering arm moves in by an amount of 16.08mm. resulting in a toe change (toe out) of 1.49mm with 100mm of suspension travel

    now obviosly this is a definite answer to the fact that there IS bump steer in s13 in ke70 suspension (bugger eh), so my question is...how bad is this? compared to what is acheivable with ae86 stuff? anyone keen to get out the measuring tape on their cars?

    comments are most welcome

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    Senior Member sr_rolla's Avatar
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    (quote old thread simon ae86)

    pretty decent findings mate,

    in your first senario... 1.1mm toe change is SFA really... so theres your answer right there wink.gif there IS bump steer, but not heaps

  7. #67
    Senior Member sr_rolla's Avatar
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    Firstly, top work KE70Dave, those graphs look very similar to the professional bump steer graphs, u get a gold star tongue.gif

    I think that 1.1mm is a reasonable amount of bump, because if the whole front end is compressed (under brakes maybe) thats a 2.2mm toe out.
    the easiest way to fix it is to do what Simon-AE86 touched on and space out the tierod end. To do this i would piss the tie rod off and use a piece of threaded tube and a rose joint (AJPS sell these) and then run a bolt/rod through the hole that tie rod currently bolts to and space the rose joint out till you have no bump steer. Also, a really acurate way to test for bump steer is to make a bump steer gauge.

    to use said bump gauge, take the springs out of the car and raise and lower the car thru its range of travell, this will tell you how much bump you actually have.

    also, KE70Dave, those front knuckles, are they made of aluminium of steel?

    If steel, i'd suggest getting the tierod mounts heated and twisted around to sit the correct way in relation to the tierod or if aluminium, machining the the hole out bigger and at the right angle, then weld in an insert that gives you the strength back. It would be a bit of stuffing around but its safer in the long run.

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    Senior Member sr_rolla's Avatar
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    (quote old thread ke70dave)

    that's an interesting contraption....still can't figure out how it works though...but i can see what its trying to do i think..

    the thing is...now that i've become aware of this apparent bump steer, damnit i can't make it steer on any bumps!!!

    i've gone over speed bumps with only one wheel, and tried to get it to bump steer, ive gone up slanty gutters pretty quick and can't get it to do anything!!!!

    so is it really that much of a problem? (the bump steer that is....the tie rod mount i can see where your coming from...but its been like that for 1.5yrs....soo.....)

    the next thing i'm going to do, is put a wire-tie around my shock absorber piston, and see how far my suspension actually travels under normal driving, and then try it going over bumps.

    the other thing is....the alternative is ae86 stuff....surely there is a little bit of this bump steer in that as well? suspension setup is all about trade offs they say....and no system is perfect.... i'm going to try and track down someone with ae86 stuff and let me at it with a tape measure, see what i can come up with.

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    Good work on copying the old thread over!!

    I am very keen to get my hands on a cusco rear RCA that does the same thing you described, lowering the diff end panhard rod mount so its basically flat, but im doubting it would make much of a noticeable difference.

    Any one tried it?
    RT142 Estate.

    AJPS.

  10. #70
    Senior Member sr_rolla's Avatar
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    Ke70dave: You wont feel it on bumps, the best place to actually feel it is under heavy braking and acceleration, as the front of the car rises and falls the toe will change either in or out makeing the car unstable (see: lowered r32 and later skyline and 300zx's as a good example of shocking bumpsteer).

    The way that interesting contraption works is as the car is raised/lowered thru its travel the front bolt will come away from the wheel during a toe in situation and the oppsite will happen (rear bolt comes away) in a toe out situation. when this happens u will know where in the travel the bump steer is occurring and by how much (the amount of gap between the bolt and the wheel) so u can fix it and test again.

    With the tie rod, i had another idea, get some spare tierods that are a little longer and heat/bend them so the tierod end is in the correct orientation, that should fix the prolem I'm concerned about.

    Also, I thought i'd put up a few piccies, The first few are of the car with the white underside belong to 1 of the TRD prepared AE86's that raced at bathurst in the 80's (the pics belong to someone on here, i can't remember who but if theres a problem using them let me know and i'll take them down). Alot can be learned fron studying these pics, especially the front end. If you look at the way the castor rod has been attached to the tubular LCA, it can pivot, this is because when the front end is rosejointed there is no longer any give from the bushes. With no give, as the suspension moves up and down or when caster is adjusted, the angle between the the LCA and the castor rod needs to change, otherwise it will try and bend or pre-maturely break rosejoints. Other than this, if u look carefully, the outer spherical bearing (where the ball joint was) has been moved closer to the disk, with this they are trying to address the scrub radius problems that this setup has. The bar with holes in it (red on the rear end photos black on the front) is the sway bar arms. This is kind of like a progression from the older more standard style sway bars to the blade adjustable bars of today. The rear end pics are just a really good example of how to do a rear end properly and the blue setup is a formula (i think) setup that AJPS was selling second hand, this is a very similar setup to the TRD setup but out of the car obviously.
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