[nickcrowhurst]

To respond to some of the comments so far:
Markdoane said
“If someone would enter the spring rates (lbs/in deflection) for the various weight bars, we could combine this with Inland Andy's recommendation for 1-2 inch bend and tell exactly which bars to order.”

Yes, exactly so, and a great idea. The equations are simple practical tools to assist in the selection of a load distribution hitch. An analogy would be the decision as to which paddle a kayaker should buy. The vendor should give advice based on the height of the paddler, the beam of the kayak, the type of water being traveled. The kayaker should then be equipped with a paddle “fit for purpose”. However, it doesn’t mean she’ll be safe or efficient in the real world situation of moving water. That will require skill, experience and judgment. Just like towing heavy.

59 toaster said
“That will once and for all put it to rest what bars with how much deflection is needed to make a DC work properly in an emergency situation and back up Inland Andy's observations about "over hitched".

My guess (and it’s no more than that, so not very helpful), is that although a certain bar tension is required for a given rig for correct load distribution, this tension could be obtained from either:
(a) A stiff bar with a small deflection, OR
(b) A soft bar with a larger deflection.

I guess that the soft bar with the larger deflection would be far preferable when the rig is traveling. When traveling over bumps, the load distribution effect would remain steadier, as a one inch deflection of the soft bars would have less impact on this effect and hence the trailer behavior would be more stable. Also, the impact loads on the trailer would be lessened, and thus cause less stress on the trailer. (Andy’s point, I believe). As 59 toaster said, this will enable more consistent sway control from the Dual Cam hitches.

2Air makes some very good points
“....i agree the trailer can function like a simple seesaw (single fulcrum lever) but the truck? wouldn't we need to know the center of gravity/balance point for the truck? most of the diesel rigs are very front heavy...until we get the beds loaded up....but still seems we'd need to know cog instead of just the overhang?”

2Air has hit on the central difficulty in analyzing this issue. In the real world, the center of rotation of the TV will depend on the relative hardness of the front and rear springs. In the past I have attempted to include these variables, but the math became too complex to be of practical use to me. By assuming the suspension is rigid, I have attempted to produce a practical, usable, set of equations whose accuracy is sufficient for the purpose. By concentrating on returning the TV front axle to its original height, I have attempted to minimize the distortion caused by the assumption.

“increasing force from 1000 to 1400 doesn't really move 1/3 more does it?”

Yes, I believe so. As you correctly state, I have concentrated on the tension in the chains, and not the required deflection of the bars. The sophisticated way to find out is by following Pick’s excellent suggestion!

I have to take my 4 year old granddaughter (number 5) out into the woods to show her how to break trail, mark trail etc, so farewell for now.
Nick.