King of the beasts test (RAM 3500 vs F450)

Well, very thick c-channels make perfect sense for class 8 trucks. There are a million different reasons to build a class 8 vehicle, but there aren't so many sales (unlike light trucks) so it's difficult to really get any economies of scale for mass manufacturing. So the entire industry has coalesced around the 34" or 36" (I keep forgetting which) wide frame. They use C-channels for accessibility reasons as well. They need to be able to upfit all sorts of bodies, axles, mounting systems, suspensions, and other things that are not proprietary to a specific company. That's why all the Cab and Chassis trucks also adhere to a 34" or 36" wide frame from the cab rearwards. It also seems like RAM's chassis cab frame is C-channel as well, again to appease the up-fitters. I'm sure if the entire industry could agree to move to a boxed frame, they would. But there are issues with such a change, many of the body/chassis mod manufacturers would have to re-tool and re-engineer lots of components that they haven't had to really re-engineer for. Again there isn't a huge mass of these specialized items being sold to begin with as well, so it takes many years for them to make enough money off their capital investments. Then there's the whole standard on what to agree on for accessibility to running stuff inside the rails like wiring and access holes/panels. It'd just get messy so I believe the industry just stays c-channel to make life easier for the OEM's and upfitters.

Engineers love to stiffen the frame. The stiffer the frame, then the finer they can tweak the suspension to perform the way they intended.