THEORETICAL tongue wt question

IN THEORY:

Scaled truck, no TT  front axle  4000#    rear axle  3500#  Total    7500#
Scaled TT unattached    Tongue 1000#    axles    9000#      Total  10,000# TT

With TT attached,  WD hitch adjusted    front axle  4200#  rear axle  4100#  Truck wt 8300#    TT axles    9200#

The WD hitch pushed 200# to front axle and 200# to TT axle, leaving 600# on rear axle.

What is the real tongue weight?? Is it 1000#, as weighed unattached and before WD hitch connected???  Is it 800# added to the truck load??
If it is 800#, which is only 8%, is this too little tongue wt?  Is it 600# on the rear axle??  6% tongue wt.??

Is the 10% tongue wt minimum measured before or after WD hitch adjustment?

Am I making a mountain out of a mole hill??

No mountain, no mole hill.
Tongue weight is 800 as measured with WD hitch engaged as you have described.
Simple math is your truck weight total changed by 800 lbs when you attached the trailer. It gained this by supporting part of the trailer weight (800 lbs) on the hitch. This 800 lbs is shown in the truck axle weights.

IMO, 10 to 15% tongue weight is a guideline for trailer handling, remembering that too little tongue weight can be just as bad as too much tongue weight. You may find that 8% in your configuration is a comfortable tow, but it would be best to try adjusting your trailer weight cargo and test drive for comparison. It's what I've done on the last two TTs I've owned and I've been comfortable at 10-11%.

Adjusting the hitch will move the 800 lbs tongue weight between the truck axles with little effect on the total tongue weight. The goals of hitch adjustment are (1) level travel trailer and tow vehicle and (2) safe controlled towing thru proper tongue weight distribution to the tow vehicle axles.
To increase weight on the tongue, move some cargo in the trailer forward and then adjust the WD spring links to compensate for any rear hitch sag.

The real tongue weight is 1000# as scaled, not 800#. After the WDH is is sprung up, part of the weight get transferred to the trucks front axle, part gets transferred back to the trailer's axle(s) and the rest is carried by the trucks rear axle, as shown by the scaled weights. If the truck was scaled with the trailer hooked up, and the WDH not sprung up, the truck would have been 1000# heavier. I think you are trying to figure out which number to use when calculating payload huh? In that case, it's 800# as that is what the truck is actually carrying. The scales tell the tale.

Two responses and two different answers already.    I guess I'll ride the center line, and say that since there's a fairly small difference between the two numbers (800# and 1000#) with or without the WDH engaged... that it likely won't matter all that much.  Unless your tow vehicle's tongue weight upper limit is, say, 800# in this theoretical example.  But then you'd probably need to think about upgraded the tow vehicle regardless, since you'd be at/near the max at all times... a condition we usually recommend avoiding.

In our forum library article Weighing Travel and Fifth Wheel Trailers, there is a reference to leaving the WDH attached (if you have one) during the weighing process.  So that would leave toward the 800# figure.  But what if you aren't using a WDH, that day or ever?  Then you are at 1000# tongue weight.

So the answer can be "neither" or "both" depending on the equipment you're using, and the source of information. 

Scaled tongue weight is just that. The WDH just does what the name implies, distributes the weight. A 1000# tongue weight is still a 1000#  when using a WDH, it's the place the weight is carried changes.

LOL!  Both answers are correct, depending on the perspective.  The actual Trailer Tongue Weight is the 1000 lbs. The weight the trailer tongue puts on the rear axle via the hitch is the 800, meaning the rest of the "tongue weight" is on the front. So, it is 800+200 = 1000.  Viewed from the perspective of the hitch it is 800#, but viewed from the perspective of the trailer it is still 1000#. Maybe it would help to think of "Hitch Weight" as distinct from "Tongue Weight".

If a 200# man stands on two feet and is well-balanced, each foot carries 100#, but his weight is still 200#, right? If he leans left or right, the weight on each foot changes somewhat, but his total weight doesn't change at all.

Gary RV Roamer said:

If a 200# man stands on two feet and is well-balanced, each foot carries 100#, but his weight is still 200#, right? If he leans left or right, the weight on each foot changes somewhat, but his total weight doesn't change at all.

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...depending on the scale he's using... because we know THOSE are never accurate! 

Yeah, but the accuracy (or not) affects all the numbers. It's still the same proportions, even if the absolute values are off.

Gary RV Roamer said:

LOL!  Both answers are correct, depending on the perspective.  The actual Trailer Tongue Weight is the 1000 lbs. The weight the trailer tongue puts on the rear axle via the hitch is the 800, meaning the rest of the "tongue weight" is on the front. So, it is 800+200 = 1000. Viewed from the perspective of the hitch it is 800#, but viewed from the perspective of the trailer it is still 1000#. Maybe it would help to think of "Hitch Weight" as distinct from "Tongue Weight".

If a 200# man stands on two feet and is well-balanced, each foot carries 100#, but his weight is still 200#, right? If he leans left or right, the weight on each foot changes somewhat, but his total weight doesn't change at all.

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Gary,
I may be splitting hairs, but in my example, with WD, rear axle was +600#, front was +200# with 200# shifted back to the TT.  Does the hitch carry all 1000#, shifting 200# forward and 200# back?  The truck is only 800# heavier.

All a weight distributing hitch does is raise the hitch point back to a horizontal posture, taking the V out of the hitch.

How much weight gets distributed to each of the 3 axles depends on each axle's spring weight and the distance from the hitch to each axle.

Without an equalizing hitch, if you put 800 lbs of tongue weight on the hitch ball, the back of the truck will go down, compressing the rear springs, while the front of the truck rises.  If the expanding springs at the front of the truck take 200 lbs off of the front end, the rear axle weight will go up by that amount in addition to the hitch weight, or 1000 lbs.

Note that the truck is only carrying 800 lbs of tongue weight but the weight distribution has shifted, adding 1000 lbs to the rear axle.

Without a weight distributing hitch, the trailer axle weights stay the same, hitched or unhitched, because the trailer's tongue weight is carried either by the hitch ball or the trailer's tongue jack.

A weight distributing hitch restores the level posture of the truck by leveraging the hitch up until the truck and trailer are riding level. 

Part of the hitch weight will be leveraged onto the truck, the rest will be leveraged onto the trailer frame and from there onto the trailer axles.

If the truck's front and rear spring rates are the same and you set the equalizing hitch to duplicate the unhitched truck's posture (i.e. make the truck level when hitched up) you'll add half of the hitch weight, or 200 lbs to each axle, or 400 lbs to the truck's GVW.

The other half of the hitch weight is transferred to the trailer frame by the leverage placed on it raising the hitch to a level posture.  This should transfer the remaining 400 lbs to the trailer axles.

All of the above is theoretical, the actual weights transferred to the truck and trailer axles depend on each axle's spring rates, how hard you crank up the equalizing bars (what percentage of the hitch weight are they offsetting?) and the distances from the hitch to each axle.

When you use a tongue weight scale you simply measure the tongue weight. You do not  use anything but the scale under the hitch. What happens after that is  irrelevant.  Just because the WD bars distribute some of the weight around does not mean you have less tongue weight.

keymastr said:

When you use a tongue weight scale you simply measure the tongue weight. You do not  use anything but the scale under the hitch. What happens after that is  irrelevant.  Just because the WD bars distribute some of the weight around does not mean you have less tongue weight.

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SHORT AND SWEET!  Thank you!

keymastr said:

When you use a tongue weight scale you simply measure the tongue weight. You do not  use anything but the scale under the hitch. What happens after that is  irrelevant.  Just because the WD bars distribute some of the weight around does not mean you have less tongue weight.

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Same thing Gary and I said. Folks seem to get testy about different people saying the same thing on here, but this is a case where at least three people said the same thing three different ways and the OP finally caught on because of the way it was stated.

I may be splitting hairs, but in my example, with WD, rear axle was +600#, front was +200# with 200# shifted back to the TT.  Does the hitch carry all 1000#, shifting 200# forward and 200# back?  The truck is only 800# heavier.

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Sorry about the different numbers. Just consider my numbers to be an example. The point remains the same; changing where the weight is carried on the truck is doesn't alter the total tongue weight. I gather you got that from keymastr's verbiage, so I won't belabor it further.

I LIKE to see the same response more than once!  It is just key mastr was the most to the point.  Thanks all for your responses

It was a good question. We often forget what weight distributing really means for the hitch. The "weight carrying" capacity of the hitch really is all the weight it can handle. The reason for a higher hitch rating with WD is that the WD can shift enough weight so that the hitch isn't actually carrying more. What goes unsaid is that you actually have to apply enough pressure on the WD spring bars so that the extra weigh is shifted forward and off the hitch.  If you don't do that, the hitch is still overloaded.

Hitch engineers would probably say the above is a bit of an over-simplification because the torque change that WD applies to the hitch when the trailer bobs or jerks suddenly, but the basic concept applies.