Buliwyf, I can't say that I agree with your assessment of boxed frames. They are stiffer, both vertically and torsionally, so that does account for alot of the marketing hype surrounding them currently. But I am unsure how you would think they are weaker? Yes a typical boxed frame has thinner wall thickness than a C channel frame, but that is because less material is needed to have the same strength. The frame on my Ram 2500 is fully boxed, and they have been since 2003. I believe that Ford is the only one of the big three still using a C channel frame on their HD trucks. Not that this is a bad thing at all because all medium duty and up trucks use a C channel frame, so they are obviously strong. Also I would have thought that a C channel would be easier to form than a full box frame? Not trying to start stuff, just curious where your info is coming from as well. Thank you.
No problem. I do odd work for a few truck companies. Was in a Bush/Nascar garage two days ago. Amazing what you can learn on a simple factory tour.
The rigidity of it, is it's weak spot. Rather than flexing like a giant piece of spring steel, all the stress of flexing or load hits, will localize to the weakest spot. Usually a weld or bolt. The C frame has more flex across the frame giving more room to soak up shock loads. When frames start getting really big, the boxed frame advantages start to drop off quick. You need to make sure they are flexible enough to not fail, and thick enough in all the right spots.
Eventually the boxed frame ends up heavier than the C frame for the same level of strength. The line where the effieciency of a box frame meets the effieciency of the C frame is right around the size of a 1/2-3/4 ton truck. So it makes sense that Dodge is trying to make a boxed frame work. It still might.
The C frames are more expensive, on the Fords especially, becuase the front of them is shaped. It loops up, then down steeply. It takes one h&%$ of a stamping machine to punch that piece out. The box frames are a simple tube, they stick it in a mold, then pump it full of hydraulic oil, the oil forces the tube to take the form of it's mold. GM makes hydroformed frames for less than the cost of Home Depot dirt.
I tend to avoid them, my Toyota's and Jeeps were rotted out quickly by all the goo that gets inside the frame. The boxed frame is a huge advantage when C&D and Motor Trend are writing your reviews, it feels livlier, but when the truck has 300k miles, it's a different story.
