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The best caster angle?

Discussion in 'Shop - Miscellaneous' started by Scott_F, May 6, 2004.

  1. Scott_F

    Scott_F Active Member

    Joined:
    Dec 28, 2003
    Location:
    Tucson, was Anaheim
    I have been designing a custom long travel center mount A-arm (SLA) suspension with several CAD programs. I feel like I have a good understanding of all the geometries and variables that I want, but I am a little uncertain about the optimum caster angle. Before I make the arms and spindle uprights, I would like your opinion on what would be the acceptable range of caster angles, and whether a little caster gain is desirable. Thanks for your input.
     
  2. ACID_RAIN28

    ACID_RAIN28 Well-Known Member

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    Oct 25, 2002
    Location:
    Temecula, Ca
  3. FABRICATOR

    FABRICATOR Well-Known Member

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    Apr 3, 2001
    Location:
    Ventura County, CA
    Yea, what he said...
     
  4. Scott_F

    Scott_F Active Member

    Joined:
    Dec 28, 2003
    Location:
    Tucson, was Anaheim
    Thank you gentlemen. I just spoke to a friend who runs a race shop, and he also said 6 degrees. That sounds like a consensus to me! [​IMG]

    Now what about caster gain? I have a design that can gain 1/2 degree at bump and droop, or should I just leave it at 6 degrees throughout? I thought a little gain at the ends of travel would provide a bit more stability when you need it most.
     
  5. ACID_RAIN28

    ACID_RAIN28 Well-Known Member

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    Temecula, Ca
  6. SLR

    SLR Member

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    Nov 5, 2001
    Location:
    666
    I would like to hear more about your design B4 I shoot advise..

    -Caster Curve-
    You will gain caster threw wheel travel. (With your pivots in the proper location)

    If you have 6* @ RH then I would guess you would be around 12* @ Bump and 3* @ Droop... + or - 2*

    Build some moack ups off your prints and get the cycling...

    Have FUNG...
     
  7. ntsqd

    ntsqd Active Member

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    Sep 17, 2001
    Location:
    Here
    Gain in bump means the truck REALLY wants to go straight. Seems like that might be an advantage when you nose dive it. I would hazzard a guess that you probably can't design a system that gains too much if all the other factors are also in range.
     
  8. partybarge_pilot

    partybarge_pilot Well-Known Member

    Joined:
    Feb 19, 2002
    Location:
    Easton, KS
    Gain in bump is neede with long travel susp. Think about how much chassis attitude change you have when you hit the brakes. You want to include about that much gain in. If you don't your car wiil get squirly under hard braking as your chassis roll will reduce your effective castor.

    If you do your mounts right you can have gain in bump and droop......
     
  9. Scott_F

    Scott_F Active Member

    Joined:
    Dec 28, 2003
    Location:
    Tucson, was Anaheim
    I do have caster gain in bump and droop, but it is only 1/2 degree. I can easily add more. It makes sense to have caster gain in bump to offset chassis pitch. Caster gain at droop would help with stability when nose diving off a jump.

    SLR, I have software that shows me all the curves for a given design. I can move the pivots around to change the caster gain, then I will have to tweak the other points to fix any problems it may cause, particularly bump steer.

    Are there any more opinions on caster gain, and how much?
     
  10. jesusgatos

    jesusgatos Active Member

    Joined:
    Feb 11, 2004
    Location:
    on the road
    I'm wondering how it's possible to get caster gain on BOTH bump & droop. I would guess that if an A-arm suspension was designed to gain caster on compression travel, it would continue to gain caster from full extension through full compression, independant of ride height. Can you please explain?
     
  11. Scott_F

    Scott_F Active Member

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    Dec 28, 2003
    Location:
    Tucson, was Anaheim
    Let's say you have the lower A-arm pivoting parallel to the chassis centerline. The lower arm and lower ball joint will swing straight up and down. The upper arm could have the front pivot more inboard and the rear pivot more outboard relative to each other. That will cause the upper arm to swing in an arc. It will move the upper ball joint in a rearward arc from ride height, whether it is moved up or down. That will increase caster.
     
  12. jesusgatos

    jesusgatos Active Member

    Joined:
    Feb 11, 2004
    Location:
    on the road
    Oh, I get it. I was picturing something like the stock Tacoma arms, where the upper/lower pivots are not parallel. In that setup you would gain castor through the whole range of travel, right?
     
  13. ESB4130

    ESB4130 Member

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    Jan 16, 2003
    Location:
    Escondido, CA
    theres that yeah. =) the more caster you got the more its gonna cut into the turns. its one of those preferance things really, on the street you dont want too much, like negative camber it will wear out the tires quicker, but in a turn, having that tire leaning inboard on the top will fell pretty good.
     

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