Help understanding control arm length and bracket stress during axle movement

[GASnBRASS]

I'd like to understand how axle movement effects relative bracket distance and control arm length during cycling.

When an axle flexes one side up and the other side down, and the axle brackets swing in an arc side to side, and the control arms swing in an arc front to rear, does that change the relative distance between brackets on each control arm, inducing a "push/pull" force on each bracket relative to the others, or a twisting force in the axle housing?

If the arms are parallel to the ground, does bracket position during flex mirror the other side and cancel each other out?

When the vehicle is lifted, and the arms are at an angle to the ground, does axle flex induce a twisting force on the axle housing as one side pushes forward on the axle during compression while the other side pulls back during droop? Or does the offset of the brackets combined with different upper/lower control arm lengths counteract this and it simply causes a thrust angle change?

 

[someguysjeep]

the link lengths are fixed as are the brackets on either end.
the joints of the CA's should have sufficient range to work through your travel zone without limiting and transferring torque to the frame or axle brackets, or at least minimizing what's transferred.

there are a lot of factors to consider and so many variables, but if your wheels move opposite directions during articulation the result will be a change in thrust angle (oh shit, should i say the words ,,,,,,,,,,,,,, dammit, rear steer) or a change in steering angle up front.
the variables your rig has in place decide how much, and if you can even notice the effects.
and ass in the seat is just gonna compensate without ever knowing.

 

[mrblaine]

I'd like to understand how axle movement effects relative bracket distance and control arm length during cycling.

When an axle flexes one side up and the other side down, and the axle brackets swing in an arc side to side, and the control arms swing in an arc front to rear, does that change the relative distance between brackets on each control arm, inducing a "push/pull" force on each bracket relative to the others, or a twisting force in the axle housing?

If the arms are parallel to the ground, does bracket position during flex mirror the other side and cancel each other out?

When the vehicle is lifted, and the arms are at an angle to the ground, does axle flex induce a twisting force on the axle housing as one side pushes forward on the axle during compression while the other side pulls back during droop? Or does the offset of the brackets combined with different upper/lower control arm lengths counteract this and it simply causes a thrust angle change?

The most important thing to understand is the mounts at the axle and the frame are arranged so they are mildly triangulated. The lowers point slightly outwards to the axle mounts, the uppers point slightly inward.

There is no way to run a trackbar which has to by design, shift the axle sideways as it cycles. As soon as the axle starts moving, the bind starts and gets worse the further it moves.

 

[GASnBRASS]

So with the arms on each side in a slight trangle, as the axle flexes, the arms on one side are both being pulled closer to vehicle ceneterline, while the arms on the other are both being pulled farther off center? This must create the slight change in thrust angle or steering angle that @someguysjeep mentioned, but apparently not enough to feel.

However, adding a trackbar, as the whole axle remains level but moves up and down over dips, it shifts side to side as @mrblaine noted. Now are the triangulated arms fighting each other? As the axle shifts sideways, one upper arm is being pulled closer to centerline while the lower is pulled farther away, but the exact opposite is happening to the uppers and lowers on the other side? Doesn't this induce a push/pull force on the brackets (or a twist on the axle)? Or is the length change so slight that the rubber of a clevite or the urethane of a JJ has enough give to accommodate this?

Sorry if this is lengthy, I'm just trying to fully understand the angles and stresses during compression, droop, and flex.