Originally Posted by ALBUQ F-1

Here's a useful paper, mostly Chapter 5 pages 31-36: http://www.keithwakeham.com/Files/ChassisDesign.pdf

He doesn't go into great detail, but the part on Ladder Frames with X-Bracing touches on the basic limitations of ladder frames: you can stiffen a section, but all that does is transfer the stresses to a weaker section. (see Wld427's post) The article's conclusion:

"... no “performance” vehicle should ever utilize a ladder frame. The only exception is that of large heavy vehicles that are specifically designed to go at slow speeds, and not to corner at significant speed, [but] hold very heavy loads or for towing. Essentially all the ladder frame is good for in today's world of automotive design is large trucks and transport trailer vehicles."

If you do some snooping on the 'net, you can find graphical computer analyses of frames under various load conditions. Even for high-performance vehicles it is pretty uniformly the case that the worst-case stresses are imposed on a frame (or unibody structure) when going up a curb at an angle, while turning, even at very low speeds. I saw one case where the stresses in that case were triple those of other operating conditions. That is the kind of stress that cracks frames. Since it is a much more common condition (turning into a driveway) than applying 1,000 HP with sticky tires pointed forward, I'd give that more consideration.

Originally Posted by jrockdiddy

Here's what I did to the factory shock crossmember.



Here's my transmission dog bone.