Assuming the formulas are correct, and I have no reason to believe they are not, here’s my question.
I load my trailer, take it to the scales, and it weighs 10,000 lbs. For proper handling my tongue weight then needs to be between 1,300 and 1,500 lbs. I adjustment the load, use my portable scales, and the TW comes in at 1,400 lbs. Now I hook up my TT using a WDH. The tongue weight doesn’t change—it still weight 1,400 lbs.—but the net downward force on the ball is LESS THAN that number.
In other words, if I’m reading this right, the raw weight (downward force) of the tongue on the portable scales is not the same as the actual weight (downward force) on the ball with the WDH engaged.
So…am I still within the recommended TW range for safe towing?