jmtandem wrote:
Which one's of us would purchase a truck with a frame that was overlapped and welded together in a typical RV factory?
Excellent point. And a point that seems to be lost on overly optimistic reliability assertions. Anybody that has interest in frame failures can research Lippert (and perhaps others) frame failures. Lippert builds about eighty percent of all travel trailer RV frames. There were documentable Lippert frame failures in both fifth wheels and travel trailers. The Weekend Warrior forums well chronicle frame issues by owners for travel trailer toy haulers 'A' frames and the frames near the triple axle on those units. Keystone has had to fix a number of fifth wheel frames built by Lippert. Many that have been on these and other RV forums remember the many frame failure threads. In the past five or so years frame failures seem to be less or folks are not posting about them.
One exception is Northwood Mfg that makes their own frames and they are overly built and not prone to failure.
There is a fundamental misundrstanding about the dropped or "stepped frame as you call it.
First of all. The main reason for the failure in the pics above is POOR DESIGN.
Tubular rectangular steel box sections are INTENDED to be loaded from the TOP or the narrow section. They are not meant to carry anywhere near their capacity in a butt joint as shown in the pictures. This was simply THE WRONG way to load that steel member.
The dropped frame IS THE CORRECT way to load that steel member, with the load on top of the narrow section and wedled there.
It is not a financial choice it is proper design.
Now that is not to say that you cannot use the box sections in other ways, you can. But you cannot load them to the same limits.
This is why I have said that the dropped frame will be stronger and ultimately more reliable. (All design elements being equal)
