Roll Cage, Back Bracing Options

[Randal]

What is the minimum amount of bar that would need to be added from the back towers to the transmission cross member? Understanding that I am running a bar from the back hoop of the cage to the shock tower.

Could I just run a bar from a plate on the rear side of the shock, midway to the top of the transmission cross member? Just a simple triangle. Would that help?

Picture below.

[McMark]

Chris, I realize my 'test' isn't very accurate. I only reference it to indicate that the cross bar is quite stable in it original form.

I think the cross bar is absolutely stable in a left-right motion. The bar is only 12" from the shock towers and that's a very short run with a boxed frame to support it. I think in the left-right direction there is very little force.

Forward-back is definitely not an issue.

Twisting along the length of the bar is tied directly to the shock towers. If the shock towers were magically solid and untwistable/unmovable, then the trans bar would never twist. Therefore, the trans bar twist is directly linked to shock tower movement.

The final force I can imagine would be for the center of the bar to move up and down due to the transmission/engine weight bouncing up and down. Since we already know the bar can handle 200lbs + gravity/acceleration of a jump, then it seems to me that the bar would not need much more support. While the stresses of racing will create forces in excess of this 200+ lbs, those forces will not be purely vertical (and if they are, then you are not in a corner, so who cares). So 200lbs at a 90 degree angle (i.e. vertical) does have some similarity to 500lbs being pulled at a 45 degree angle up and left/right.

I still maintain that shock tower movement in turn moves the trans bar, and that a solid, unmovable shock towers would mean that the trans bar is solid as well (in every respect that's important).