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Caster change with steering

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  • Matt93SE
    replied
    Your average Zilvia poster never got to physics in high school.....

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  • Def
    replied
    SAI also goes through the ball joint, it's the other inclination plane perpendicular to the caster plane. So no it doesn't change... I'm just trying to make sense of the madness that is probably some 17 year old's online rantings of suspension dynamics who got a C in high school physics (i.e. average Zilvia poster).

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  • Spoolin6er
    replied
    Haha, that's why I came here! But I have to a little, as much as I hate it, there is a lot to be gained from experience over all theory - even if their reasoning why something works is off. That and along with autox, I drift (don't tell anyone haha).

    Anyway, caster is definitely the physical angle of the steering axis from vertical in the side view. But it does seem that its calculated (not necessarily measured) by camber change withthrough a fixed steering angle). But how is that accurate if SAI influences camber change as well.

    SAI goes through the ball joint too though, so I guess it shouldn't change either right? But i guess scrub does?

    Sorry I guess this turned more into a sanity check thread haha

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  • Matt93SE
    replied
    I think you have the definition of caster slightly off.

    As Def mentioned in his first post, the easiest way to think of caster is the change in camber over steering angle...

    i.e. The standard way to measure caster with a manual gauge:
    0. mount gauge on car with wheels straight ahead. measure camber.
    1. Turn your wheel 20 deg to the left,
    2. zero the bubble level.
    3. now turn the wheel 20 deg to the right
    4. read the gauge. this angle is the difference in camber change over the 40 deg of steering rotation.

    so you're measuring the change over a specific distance and calling that a specific number.

    Make more sense? (Forget what you read on Zilvia. 99% of it is wrong.)

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  • Def
    replied
    I'm with you, the geometrical relationship that defines caster do not move. So how can it change with steering?

    Maybe he's talking about SAI?

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  • Spoolin6er
    replied
    Obviously, but does caster itself change with steering angle? It looks like it does looking at the strut angle as you turn, but it seems like it wouldn't since the lower ball joint and strut top do not move with steering (right?).

    This quote from zilvia is what got it in my head, just didn't make sense to me...

    "Caster is a dynamic figure of a vehicles alignment. The more the wheel turns, the more positive caster is achieved. For example, if your 240sx has 6 degrees of caster around 20 degrees of wheel angle ( close to factory), then there would be around 18 degrees of caster at 60 degree wheel angle."

    thanks for the help

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  • Def
    replied
    Caster causes changes in camber wrt steering angle.

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  • Spoolin6er
    started a topic Caster change with steering

    Caster change with steering

    Hi guys,

    Its my understanding that as steering angle increases, the caster changes as well (as well as camber and toe). What is the mechanism that causes this castor change? Is it really changing or does it just look like it as the strut changes angle through the steering sweep? I say this b/c the lower ball joint stays in the same spot right?
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