I will also add that I realized after recaluclating using the 3500's numbers, I was doing "combined axle rating." So I wanted to go back and do only REAR axle rating calculation.
Assumptions- Mostly the same as before; except I'm going to split the family 50/50 between the front and rear axles.. it's probably a good enough approximation.
- family+in-cab stuffs: 300lbs for rear axle calculations (splitting 600lbs of family+snacks between two axles), or 225lbs ((600-150)/2) for payload calculations
- I couldn't find the exact same vehicle used
here but a close approximation is a 2014, 2500 CrewCab, Short Box, 4x4, Laramie... 2180 payload, 7818 curb weight, 6000f/6500r axle ratings, 17,010 trailer max. So we'll go with that.
5th wheel hitch ~150lb
payload method: 2,180 - 225 - 150 = 1,805lb
REAR axle method: rawr (6,500) - rear base weight (2,969) - 225 - 150 = 3,156
** This method actually brings them closer together
somewhat .. available 'payload' increases by 300lb and available rear axle rating decreases by ~800lb. And probably a much better approximation anyway because the 5th wheel is going to be MOSTLY on the rear axle.
So in these equations, kingpin weight limit yields between 16% rv gvwr to 20% rv uvw using the remaining 'payload' numbers, and again easily handles the full 25% rv gwvr (2,750lb) with 400lb to spare. backing off to 22.5% (2,475) increases the safety margin from 400lb to over 650lbs.
..dane
