Wishbone Loading Scenario

[motorsportfan12421]

Hello,
I was recently reading RCD by Derek Seward and in one of his chapter about wishbone stress analysis he shows a double wishbone setup with the pushrod attached to the bottom wishbone outboard pick up point. He goes on to state that under vertical loading say as such due to down force and weight of the car only the pushrod and bottom wishbone resist the load. Then by assuming the wishbone is parallel to the floor you can quickly see in the FBD that all the vertical load in max vertical loading scenarios is resisisted by the push rods. Then by taking moments around outboard pick up points you can find the forces in the 5 other members.

I was wondering that if the lower wishbone isnt parallel to the floor would it support some of the vertical load? Also why does the upper wishbone support no load? I understand the bars are only uniaxially loaded due to rose joints at either end but surelly in full heave the bar would extend as the chassis outboard and inboard points are now further away. So in max heave which occurs at max vertical loading way are we not seeing the wishbones support vertical laods and why is it only the pushrod doing so?

[Greg Locock]

If the lower wishbone is not // to the floor then yes it will react some of the vertical load. In practice the upper wishbone does react some vertical load because the CP isn't directly under the lower wishbone to spindle balljoint. I'm not sure why you'd over simplify the FBD to this extent.

Figure 2 in this paper shows a more realistic geometry , slight niggle, CP is P10 in adams/car (which seems to be where the hp numbers come from), wheel centre is P9

https://iopscience.iop.org/article/10.1 ... 032022/pdf