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Thread: roll axis and cog

  1. #16
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    Quote Originally Posted by RacingManiac
    Between individual wheels of the car yes, overall total amount no. Assume if the car can generate the same amount of cornering force with a high roll resistance setup as a low roll resistance one, then the total load transfer between the 2 setup will be the same provided that the track and CoG height are equal. But that is unlikely as a car with more roll will likely degrades other handling traits as well, thus reduces the overall cornering force.
    isnt the definition of load transfer the redistribution of vertical force between the tires ??

    i dont understand what you're trying to say

  2. #17
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    Quote Originally Posted by KnifeEdge_2K1
    but as a car tries to roll, the suspension components (which remain flat relative to the ground) try to resist the roll, which adds to load transfer
    I am not following why the suspension is adding to the load transfer.

    Without the suspension some total load transfer is going to be generated. With the suspension the same pure load transfer will be generated plus some weight transfer. Looking at lateral transfer only, why would the suspension kinematics transfer additional load?


    Quote Originally Posted by RacingManiac
    Assume if the car can generate the same amount of cornering force with a high roll resistance setup as a low roll resistance one, then the total load transfer between the 2 setup will be the same provided that the track and CoG height are equal.
    The high roll resistance vehicle can be assumed to be a rigid body with no suspension, then again the total load transfer will come from the forces acting about the CoG (pure load transfer).

    The low roll resistance vehicle, assumed to be a rigid body with a highly compliant suspension should have the same pure load transfer component with the additional weight transfer component. So the total load transfer will be higher with the low roll resistance model.
    "In theory, theory and practice are the same. In practice, they are not."

  3. #18
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    ok, this is getting way too complicated

    2 examples, the cog is above the roll axis like a regular car. As the car turns into the corner centripetal force will cause the cog to move out, which translates into torque about the roll axis, this translates to putting higher load on the outside wheels then the inside wheels correct ??

    now in a car where the cog lies below the roll axis in teh same situation
    the centripetal force will cause the cog to move away from the inside of the corner, this translates to torque about the roll axis but in the opposite direction of the first car, this means the inside tires are increasing in load this time

  4. #19
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    lil diagram
    Attached Images Attached Images

  5. #20
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    Quote Originally Posted by KnifeEdge_2K1
    lil diagram
    I am assuming that the black arrow acting on the CoG (black dot) represents the centripetal force. If so, should the centripetal force be acting through the roll center (red dot) and on a line that passes through both the roll center and tire contact patch?

    I thought it was something like that, but I have not looked at any vehicle dynamics lately.

    Either way the centripetal force should definitely be pointing towards the center of curvature, and theoretically if it was through the roll center it would still work out the same as the moments would keep the same sign/direction. So your assumption should be correct.
    "In theory, theory and practice are the same. In practice, they are not."

  6. #21
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    nope, the centripetal force is just the sum of the forces on all the parts of the car, and is thus represented by just one big force on the CoG

  7. #22
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    Quote Originally Posted by KnifeEdge_2K1
    nope, the centripetal force is just the sum of the forces on all the parts of the car, and is thus represented by just one big force on the CoG
    If that is the case than that is fine, but the arrow should be pointed in the other direction since the car is accelerating towards the inside of the corner. The force must be in the same direction as acceleration.
    "In theory, theory and practice are the same. In practice, they are not."

  8. #23
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    nono, that is the centripetal force, throwing the car out of the corner, the force pulling the car in is generated by the tires

  9. #24
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    Quote Originally Posted by KnifeEdge_2K1
    nono, that is the centripetal force, throwing the car out of the corner, the force pulling the car in is generated by the tires
    The force generated by the tires is the centripetal force. The force acting on the body is transmitted from tires through the suspension arms, and that is where I was going with it acting through the roll center.

    There is no force acting outward on the vehicle, only the illusion that it is due to inertia.


    Quick link on centripetal force, not to be confused with “centrifugal force”:

    http://hyperphysics.phy-astr.gsu.edu/HBASE/cf.html
    "In theory, theory and practice are the same. In practice, they are not."

  10. #25
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    Quote Originally Posted by Alastor
    The force generated by the tires is the centripetal force. The force acting on the body is transmitted from tires through the suspension arms, and that is where I was going with it acting through the roll center.

    There is no force acting outward on the vehicle, only the illusion that it is due to inertia.


    Quick link on centripetal force, not to be confused with “centrifugal force”:

    http://hyperphysics.phy-astr.gsu.edu/HBASE/cf.html
    but as far as the car is concerned there is a force

    it's like when you're standing on a train and it stops, do you not get thrown forward ?? for you, is there not a force which pushed you forward ??

    it's the same reason why cars squat during acceleration, the tyres are accelerating but the body wants to stay still, and thus the cog is "pushed" back which transfers load to the rear tyres

    i know the force isn't "real" but for all intents and purposes it IS real

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