[theastronaut]

Keith, I didn't take it that you were trying to pick a fight, and I appreciate the info you posted. I hope I didn't come across as too defensive of my ideas. I do agree that it would be helpful to double the frame, but I still think the most effective way to limit torsional twisting would be to box the frame and add an X brace. If I can keep the distance between the rails constant, there won't be anyway the rails can twist. I will be fully boxing the frame front to rear, and won't have any gaps like you mention. I don't want a weak area that will crack. I'm even going to cut out the existing crossmembers so I can fully box the frame without missing any areas.

I may be wrong, but I don't think the forces on a frame rail will ever even get close to 55,000 psi, especially if boxing the frame to spread the load out over a larger area. I think that any failure of the frame will result from metal fatigue and cracking. Hopefully, spreading any load out will keep the metal from becoming stressed and cracking. The welding wire I use is ER70S-6 and has a tensile strength of around 79,000 psi, so the weld itself would be stronger than the metal around it. We have done destructive test of our welds and found this to be true; the metal fails before the weld does.