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Ackerman ?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Stylzz, Oct 30, 2002.

  1. Stylzz

    Stylzz Registered Member

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    Ok what the hell is it? I know it has something to do with steering but just wanted to know what it is and how to check it and how to eliminate it.
    Thanks,
    Joe
     
  2. imiceman44

    imiceman44 1 ton status

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    It's the Caster angle if I am not mistaken.
    It's the angle of the line going through the upper and lower ball joint on your axle, and the vertical.
    You want that line to be slanting backwards, (I forgot if it's called negative or positive.)
    Imagine a bike's front tire, that is what keeps it going straight if you let off the handle
     
  3. Stylzz

    Stylzz Registered Member

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    Thanks, I hear people talking about it with regard to stock cars and wanting to get rid of it but I dont see why it would be a bad thing. I mean street cars are made to go around corners so it must be there for a reason.
     
  4. Shaggy

    Shaggy 3/4 ton status

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    <font color="green"> It's not Caster. Akerman angle has to do with steering geometry, the Ackerman angle is the difference in how much one wheel turns compared to the other. Ever notice how when you turn all the way to the lock the inside tire is turned alot farther? That's Ackerman. It has to do that since the outside tire travels in a larger radius than the inside tire when you turn the truck. </font color>
     
  5. imiceman44

    imiceman44 1 ton status

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    OOPS sorry /forums/images/graemlins/frown.gif
     
  6. grumpy

    grumpy 1/2 ton status

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    Ackerman - Rudolf Ackerman is a man who worked out a steering system for horse-drawn carts, and we use his name today to describe the angle of the inside tire in relation to the outside tire when the wheels are turned to full "lock"--the farthest the wheels go to the left or right. Normally, when the front wheels are turned all the way left or right, the inside wheel is at a sharper angle than the outside wheel. If you extend the center line of each front tire to a point where the intersect and measure that angle, that is the Ackerman angle. Ideally, for perfect steering, the Ackerman angle will cross at the center line of the rear axle.
     
  7. jimmy88

    jimmy88 1/2 ton status

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  8. Shaggy

    Shaggy 3/4 ton status

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    <font color="green"> Wha? /forums/images/graemlins/confused.gif Go out and turn your wheels from one side to the other... Straight axles with simple tie rods use the ackerman principle too... If they didn't the tires would squeal like crazy when you turned. the geometry of the arm on the steering knuckle is how they make it work.</font color>
     
  9. jimmy88

    jimmy88 1/2 ton status

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    Then why did DANA (the manufacturer of the axle! they should know) tell me on the phone that Dodges with the diesel experience a lot of tire scrubbing due to the added weight on the tires and the lack of ackerman angle? Ackerman angle is toe out on turns. What your talking about is more likely due to the SAI or steering axis inclination.

    Its getting late here, but I read somewhere it said specifically there was no toe out in turns built into the straight axle steering. When I find it I'll pm you. If you find proof otherwise let me know.
     
  10. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    UM.....no the steering angles are different for the left and right tires on a striaght axle also. Thus ackerman angles. It has to do with the steering arm position relative to each other. The steering arms are moving in a circle while the drag link is moving them linearly. or something like that...hehe

    mike
     
  11. Shaggy

    Shaggy 3/4 ton status

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    <font color="green"> Well, maybe that's just a problem with the geometry that Dodge built into their axles. All I know is, look at ANY straight axle truck built in the last 50 years or so, and it's exceedingly obvious that the inside tire is turned significantly more than the outside tire. </font color>
     
  12. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    Lack of ackerman angle means that the design of the suspension is not perfect. Ie. The tires will not track the exact circle the the truck is driven in. If the tires where truely parrallel at all times.....I really don't even want to know what it would be like to drive but it would be bad.

    mike
     
  13. jimmy88

    jimmy88 1/2 ton status

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    Evan &amp; Mike, thanks for setting me straight. Mocked up the suspension on cad and did indeed see some ackerman angle. Guess you can't always trust the information you get from "expert" sources (or maybe I was just speaking with the janitor). Check out this link and scroll down to ackerman http://www.aligncraft.com/performance/primer.html.

    One question though, if its not lack of ackerman angle then what causes the tires to wear quicker on straight axles, or is that just a myth too?

    Jim
     
  14. Shaggy

    Shaggy 3/4 ton status

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    <font color="green"> I've never heard that tires wear faster on straight axles; although with the thing about the Dodges, I have noticed that alot of Dodges out there have seriously feathered edges on the front tires. Maybe Dodge set up the geometry like that for some reason? I'm also curious as to what the difference in the feel of an axle is that came off of a big truck like a crew cab K30 after it's put into a Blazer. I've never heard anything bad about it, so it must not be a big deal. </font color>
     
  15. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    I have seen/heard that tires wear differently (usually faster) on straight axles due to the fact that since the tires are possitively connected the force(s) at one tires directly affect the other. Not only the tie rod, but the tube/balljoints/knuckle keeps one tire in certain relations to the opposite tire (much more so than an independant setup). Road surfaces are rarely ideal for any setup, but moreso on solid axles. If the road is uneven, one tire may be in perfect contact with the road while the other is not, or in most cases both tires "comprimise" on a contact patch and a tug of war exists between the two (causing added wear). Independant systems allow the tires to contact the road ....well.....independantly and more uniformly. From what the "guys" say who run the alignment machines is that although tires mounted on solid axles do wear faster, it is NOT a huge difference in the life of a tire. They attribute the added wear of solid front axle tires to additional "scuffing" induced from uneven contact with road surfaces. They say improper toe will cause more wear than the difference between solid and IFS.

    I have felt tires on properly aligned solid axle trucks and you can feel a scuffed/feathering affect not detectable on properly aligned IFS systems 2or4WD.
     
  16. Shaggy

    Shaggy 3/4 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    I have felt tires on properly aligned solid axle trucks and you can feel a scuffed/feathering affect not detectable on properly aligned IFS systems 2or4WD.

    [/ QUOTE ]

    <font color="green"> I notice the same thing, but in some cases the IFS trucks are much worse, especially when the IFS trucks are lifted. Especially in Dodges; my brother had a 98 Dakota with a lift on it, he couldn't get tires to last more than 10k miles on the thing because the edges wore so bad when he turned. It was just the way it was, the lift was installed correctly and the alignment was fine. Even on stock trucks you notice that when the wheels are turned to the lock the inside tire looks as though it is tipped precariously far over.

    Personally I notice unevenly work tires much more often on IFS trucks than SFA ones. In stock form what you said may be true, but for lift trucks, this is just one more reason that SFA is better. /forums/images/graemlins/thumb.gif

    BTW, I'm not arguing your point, just throwing more of my observations into the mix. </font color>
     
  17. imiceman44

    imiceman44 1 ton status

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    It's funny I just got my last issue of OFF ROAD and they were talking about the akerman angle.
    I had heard about it before but since it's something I couldn't really change on my Straight axles, I just let it sit back in my head. Shaggy got it right.
    By the way, for lifted IFS it's not the akerman that makes the tires wear faster, it's the constant change in camber that makes the tires wear on the inside more than the outside. Actually the stock setup already is negative camber, and because of the short and long A arm configuration, when you lift it it will have more negative camber, unless your kit changes the whole geometry, which is not the case in many aftermarket kits, or when people just crank up the torsion bars.
     

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