Redrilling steering arms and ackerman angle

Thread in 'Technical' started by royal, Dec 1, 2008.

  1. royal

    royal S1- F.T break!

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    Has anyone looked into this at all? I've seen a few threads lately where people are redrilling their arms closer to the hub so (if I'm understanding it right) it will reduce the ackerman angle difference between the wheels? Seems to me a better idea is to cut the arm and reweld it angled in a little bit to get the angle difference back? Is it even worse worrying about?? :smash:
     
  2. MJG

    MJG Active Member

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    Ackerman is the distance of the tie rod ball joint from the imaginary "straight ahead" axis of the hub pivot point (track control arm ball joint). If the car had zero ackerman the tie rod would mount (any distance forward) directly in line with the track control arm ball joint. If the tie rod mounted a little bit inboard of this it would add ackerman.

    Having the tie rod mount closer to the track control arm ball joint/strut pivot point just increases the amount the wheel turns in relation to the steering rack's travel (smaller radius on the imaginary curve of steering means it travels more angle for a set lateral distance.

    Cut/weld or redrill doesn't matter, do whatever you want to have a strong steering joint in the right place you want it.
     
  3. Polo

    Polo Sr20 parts man!

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    Iv looked into this but i cant get my small head round it:wack: I know how it works, why its there etc, i just cant figer a way to get zero ackerman angle!!! I think. looking at most cars, if you could get that trailing wheel the same angle as the leading one, youd be able to skid some mental angles!!
    You see alot of Ke's and 86's with no ackerman angle:nod:
    Im sure theres lots of way and im sure loads of people in the uk have sused it but im also sure they wont be telling every man and his dog;)
     
  4. -WJ-

    -WJ- Dutch drifter

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  5. royal

    royal S1- F.T break!

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    Thanks for the replies guys.
    Polo - I'm not sure if theres more than I understand to the mechanics of it or not but I thought that the ackerman angle was created by making the steering rack (and tie rods) width shorter in relation to the track width between the wheels. So if you just cut the knuckle arms, like in -WJ- pictures, then you'd reduce the ackerman angle difference between the wheels? Pretty sure Mikes post confirms that as well?
    Do you think its an advantage in drifting to have zero ackerman angle then? So the wheels wouldn't toe out when on full lock. Thats what I wasn't sure of, is it better to keep ackerman angle or to get rid of it?
     
  6. MJG

    MJG Active Member

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    Move the steering mount points on the hubs further outwards so they are in line with the pivot point on the hub from the TCA, parallel to the hub face. This is zero ackerman. Declan's done it but not sure how he found it.

    Moving the steering mount points closer to the TCA mount/pivot point just increases the angle the hubs twist with a given steering rack travel. Moving the rack closer to the centreline of both hubs would (I THINK) also increase steering lock, but most racks are pretty damn close anyway.
     
  7. topi

    topi KlutchKickKidz

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    Or accept that in drifting, its more about how many beers you've had the night before haha.
     
  8. sideways.taff

    sideways.taff - www.tafftune.com -

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    Theres more to it than that but that'll get you close to zero yes.
     
  9. royal

    royal S1- F.T break!

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    Nice one, thanks for explaining Mike and everyone :) I was chatting to Julian @garageD about it the other day and been looking at it since. I think I'll be heavily limited on the Rex by the lower arm and possibly chassis leg. May have to limit the wheel width and/or offset. I'd like to properly widearch the car with custom suspension arms and trying to work out if I can add stuff to help the steering lock. Havn't had much of a chance to look at it on the car though because I've been playing engines this last week or two.
     
  10. MJG

    MJG Active Member

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    Bryn, how is that not entirely zero ackerman? Is it to do with the offset of the steering rack from the centre line of the two hubs? I'm sure I could figure it out on Solidworks but I cba! lol. More important things to do like change driveshafts and fuel tanks :smash:

    I'll be developing my stupid front wishbones over xmas Bryn, so get your tech-head on :D Going on the principle we discussed and with a big increase in track to get the lock. Also got a few steering racks I'm taking apart to try and make a hybrid or get the innards of the best one modified :D Extra teeth on the rack :wack:
     
  11. Polo

    Polo Sr20 parts man!

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    Yes moving the rack forword is one thing iv been looking at, it will maybe not give any more lock but should reduce the risk of going over centre:nod:

    And yes, zero ackerman angle would help, im sure? look at most s body drifty pics, the trailing front wheel is not pointing in the angle of direction(basicly being dragged) is why the inside edge of the tyres wear so much:nod: But weather you need that drag to stop you from spinning or not is another thing:wack: Im sure you can get used to it:D
     
  12. MR-steveo

    MR-steveo TNS MAN CHILD

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  13. james

    james Administrator
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  14. sideways.taff

    sideways.taff - www.tafftune.com -

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    Zero Ackermann would be when the theoretical line between the outer steering balljoint position on the hub and the lower control arm balljoint runs parallel to the same line on the other side (when viewed from above). Zero Ackermann means that those theoretical lines should always run parallel at any given steering angle.

    In theory you should actually want to go further than zero if you want to avoid having tyre scrub on the inner wheel whilst on opposite lock... Would be interesting to set up a datalogging system to see at what angle each wheel is turning at a given drift angle and then you'd be able to calculate the amount of Ackermann you'd want for it to be right... interesting shiznit..


    As for the E30 arms, I think we pretty much covered the theory of what you needed to do, you just need to factor in some adjustability just incase you're slightly out with measurements. For some reason my e36 rack runs out of teeth before the tie rods hit the body so I'd be interested to see if you can sort out extra teeth on the rack. Its completely possible just I dont trust myself to strip a rack and put it all back together properly lol.
     
  15. royal

    royal S1- F.T break!

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  16. Polo

    Polo Sr20 parts man!

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    Ahh, nice one Steve!! Lol, i should have dug out all my college papers, its all in there:wack:

    Thing is thogh, that demo, yea it shows zero ackerman angle but that actully reduces the angle on the inside wheel. That kart does have prety week lock thogh:euge::D
     
  17. Paz

    Paz -NIGHTSPIRIT FAMILY-

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    Im guessing thats why most people shorten the knuckle at the same time, to get some of that lost lock back? I dunno..

    Also, the trailing wheel on most drift cars barely touches the floor anyway? As its mirroring the leading wheel its just the inner most shoulder that drags on the floor so im not sure how much of an effect it would have with such a minimal contact patch anyway? I'd like to do it, just to see if its possible to actually tell a difference.... But usually, nothing makes a difference and it all feels the same.. haha..
     
  18. MJG

    MJG Active Member

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    As I thought then Bryn, cheers. I have several machining contacts so will see what I can do, extra teeth would be gangstaaaa. PS - stripping a rack is easy peasy, I'd never even dabbled before but I stripped my spare e30 rack just fine.

    Remove rubber cap and circlip from top of valve body where the pinion input shaft is. Undo the plug on the bottom of that bit under the rack itself. Then undo the nut inside it and you can pull/push out the pinion through the top. Remove inner tie rods, then on the passenger end of the rack, pull out the plastic plug that looks like something to do with PAS, and poke out the metal lock ring. Then pull the rack all the way through that way and yank out the block that the lock-ring just released.

    Terrible description, but anyway it's self explanatory.
     
  19. tomo1

    tomo1 New Member

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    I'm trying to find a bit of info on getting a quicker rack (or the same effect) for my track s14 -drifting to me is a skill I apply when I've got it wrong haha!- so was quite intrigued by this thread...

    The talk of anti/zero-ackerman is quite interesting, as on race cars if you assume the outside tyre is the one that governs the rate of turn then anti ackerman is used it's to increase the total grip over the front axle by bringing the unweighted tyre to a slip angle that is back towards it's peak efficiency, as with ackerman it's gone past that point... but with drifting the weighted tyre is the outside (so this is the one I assume as the governing wheel), so you want the inner to be at a lower angle to hit the peak efficiency slip angle... which with standard ackerman you have! ...so anyway, the end of that bit of tech-geek rambling is that maybe reducing to zero is a step too far?!!

    ...Pah!! All of this "turn right to go left" malarkey confuses my brain!!

    *EDIT*

    actually, after drawing a vector diagram I think having anti-ackerman will mean you can end up with a similar amount of drag on the unweighted tyre, but with it at an optimised slip angle for giving a positive contribution to the steering correction- i.e same amount of tyre wear, just that it's useful to the drift/skid!

    oh, and Yes I do realise this conversation I'm having is 100% with myself... stupid gripper!! :D
     
    #19 tomo1, Dec 22, 2008
    Last edited: Dec 22, 2008
  20. cptsideways

    cptsideways Active Member

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    I've pretty much got a reverse ackerman set up on my Soarer

    [​IMG]

    And now even more lock!

    [​IMG]
     

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