"off-roading" - frame twisting in a C

Thanks for all the informative replies.

DiploStrat wrote:
vibration, as from washboard and pot holed asphalt, is a much greater danger than the odd twist, especially as the washboard goes on forever

pnichols wrote:
we go VERY SLOW (7-10 MPH) on washboard roads..We also travel on canted offroad surfaces VERY SLOW ... picking our track very carefully so as to absolutely minimize the front being twisted one direction (i.e. counter clockwise) simultaneous with the rear being twisted the other direction (i.e. clockwise).

Good advice. Arriving I picked the track carefully and slowly; but when departing drove straight out at walking speed and heard the twisting/creaking. It was just one off-camber whoop. Regarding washboards, I realized the need to slow down and run recommended tire pressures (not 5+ psi) to minimize transmitted vibration and jolts.

pnichols wrote:

It's the end-to-end length-wise torsional twisting of the frame - if the frame isn't strong enough versus the weight it's carrying to remain in a plane - that does the real damage to the coach if three-point or other ultra-isolation techniques aren't used between the coach box and the frame. "Remain in a plane" does not mean the frame has to be level - the frame can be tipped width-wise or length-wise on bad roads - it means that all four frame corners must remain flat relative to each other so no coach box bending will result.

Exactly. I previously only considered approach/departure angles and ground clearance, but am now acutely aware of the torsional twisting constraint. If the suspension were fully compliant, looks like my 13K E-450 has about 6" remaining compression front and rear. If the front compresses 6" and the rear extends the same amount, hopefully frame/box twisting would be minimal. Guess the short answer is if you hear creaking you've exceeded the suspension or frame stiffness. Ballpark maybe less than one foot height difference diagonally.

DiploStrat wrote:
The new Tiger Siberian and Malayan models are playing with a form of pivot mount, especially needed on the larger Siberian on the more flexible Ford frames. As expected, however, this adds weight, cost, and height. ;-(

That's the model(s) I was thinking of. COG looks high. The conventional tigers likely do well because they don't have the long cantilevered box typical of larger C's. A short-stiff rig like pnichols would also fare well.

If not for the conveniences of a Class C; could have just thrown my Hi-Lo on a UniMog. Well that and $$$ He knows how to have fun