Thor Forums

[Chance]

Originally Posted by Judge

One other thing on my mind last night while lying bed....

How do they maintain structural integrity of the house "box" when they use a full wall slide-out?

At most there is one stud running from the floor to the roof in the very front and one in the very rear of the wall with the slide.

While the passenger side has a large window, there has to be a few studs running from the floor to the roof along that side of the coach. You would have to think the driver side would be subject to more flexing based on the design.

The only other Super C that I have found so far with a full wall slide is a Newmar. So while their quality is supposed to be very good, a full wall slide is not unprecedented. There are also several C's out there with a slide out right up against the Cab-Over so obviously they don't seem too worried about the slides weakening the box structure.

Number of studs would not be my primary concern if analyzing the structural integrity. I’d worry more about how the roof structure is supported over the long slide’s length, and what structural provision there is in place to resist (can’t be prevented) the large opening that makes up the slide to go from a rectangle to a parallelogram when the motorhome twists — and it will. To be clear, I’m not talking huge movement. It doesn’t take much displacement if the component resisting can’t yield much before failure (like screws between parts trying to move apart).

My best guess is that they try to make the roof, passenger wall, and floor act like a “C” channel to give the house structure some stiffness, but I doubt it works adequately. If the chassis and house body structures were actually stiff enough to resist twisting, there would be no problem opening and closing slides without first leveling the motorhome. I expect that when motorhome is not level, the structure can be twisted just enough that as the rectangular opening in slide wall tries to become a parallelogram, it could bind the slide box, making the drive motors have to work harder; or unable to move at all.

The only solution I’m aware of (other than not have a slide at all or make it/them much smaller) is for the chassis to be so incredibly stiff that it can’t twist a significant amount. Unfortunately, I’ve only seen that type of construction on luxury diesel buses. One company even made a video of their slide opening and closing repeatedly while the bus was parked with one front wheel way high.

Bottom line is that truck frames built with open “C” channels are not very stiff in torsion, and will twist a considerable amount as the truck is driven over uneven surfaces. If the RV body isn’t designed to twist some along with chassis, I expect they’ll pull apart after a while.

By the way, the real test will be when 4X4 F-550 motorhomes are driven off-road. I’m curious what problems they’ll encounter with entire structure.