Originally Posted by PteJack
As for the advertised "broucher" pin rate on a 5th wheel being the max the pin can carry, I am learning from 5th wheel owners that is is not the case. I am being told that it is the actual dry weight of the pin when the unit sits on the hitch plate and the unit is dry. As you add weight to the trailer, the pin weight will flucuate up or down dependent on where you place the load in relation to the trailer wheels. (Normal teeter-totter effect applies.)This has also been confirmed by RV dealerships. ALSO this logic from my second calulation is NOT true, the weight of the towed vehicle is constant. There is no transfer of to the tow vehicle through the pin. If the weight of your trailer is 10820lbs and the pin weight is 2065, when you tag up the weight of the pin is pressing on the truck and is not subtracted in any way, shape or form from the weight of the trailer, the weight of the trailer is still 10820lbs on the trailer axles. (Confirmed by the RV Dealership and so much for my perspective of simple physics.)
Someone is giving you bad information. If the trailer weights 10820 lbs and the pin weight is 2065 lbs, then the trailer axle WILL weight 8755 lbs; don't let anyone tell you otherwise. Here is where the proof comes. If your truck has a curb weight of 7392 lbs and your trailer weighs 10820 lbs, then the combined weight on a scale will read 18212 lbs. If it doesn't, the scale has a problem.
If you add the axle weights of the combined unit, they will add up to the same 18212 lbs (+/- a tad for scale grad size). If not, then either the scale is bad, or the scale approaches are not perfectly level.
If the pin weighs 2065 lbs and is placed on the 5th wheel hitch in the truck bed, that same 2065 lbs will press down on the truck and the rear axle weight will increase. Likely, the front axle will change weight slightly up or down depending on the exact placement of the 5th wheel pin. Hopefully it will increase slightly. At this stage the difference between the curb weight of the truck and the scaled weights of the front and drive axle combined will equal 2065 lbs, netting the trucks scaled weight at 9457 lbs.
If the trailer axle weight did not change, then the unit weight would be 9457 + 10820 = 20277 lbs. This would mean that the combined unit would increase in mass by the exact amount of the pin weight thereby defying the laws of physics as we know them, and if this can be proved to exist, I will write the science paper on this and retire with more money than I know what to do with, so will take $75K from the windfall and use it to get you the DRW unit you want.
You can confidently inform the dealer/RV dealer/etc. the the trailer axle WILL weigh the gross trailer weight less the pin weight. The laws of physics dictate this which is why they are laws.....not the general suggestion of physics.
Your math is good; very good in fact.
The part that I am not convinced, is the specified pin weight of the trailer. I am not confident that those that should know, do know.
As for the 'trailer weight' (ie towed weight), that is NOT affected by the pin weight as whether the gross weight of the trailer transfer any weight to the truck or not, the actual trailer weight will remain the same. The trailer axle however, will vary.