True, most people will NEVER load their trailer to its GVWR, but then the question begs:
What weight number do you use?
It's somewhere between the "dry" weight and the GVWR, but where?
Start with a realistic estimate of "dry" weight.
If you're looking at an existing trailer, use the value from the federally-mandated sticker.
If you're shopping online, Google the make and model and you'll probably find dealers' websites which list the factory-delivered dry weight or show an image of the sticker.
First, check to see how much cargo capacity the trailer has.
If you tend to load lightly, add 500# to the dry weight,
If you tend to load moderately, add 1000#,
If you like to take a lot of stuff, add 1500# -- unless that would exceed GVWR.
If you have a trailer with 4000# of cargo capacity and really believe you'll load it to the GVWR, use the GVWR.
Keep in mind, this thread is about selecting WD bars.
WD bar ratings probably still are based on the out-dated assumption that the WDH will be adjusted to transfer equal loads to the steer and drive axles or to achieve "equal squat".
The modern approach to WDH adjustment (return steer axle to unhitched weight or slightly less than unhitched) requires less load on the WD bars.
So, if you under-estimate the tongue weight a bit, you'll probably still have sufficient WD bar capacity.
Going by GVWR is SAFE because it's the realistic worst-case scenario. At that point you don't even have to weigh it because you already KNOW that you're prepared for any realistic possibility.
If you don't know the dry weight, and/or
if you don't know how much you are loading, and
if you don't weigh the loaded trailer,
how do you KNOW you've not exceeded the GVWR?
Based on what I've read on Open Roads Forum, exceeding the GVWR is a realistic possibility.
Barney, thanks -- I know he is talking about trailer GVWR.
---I think, even according to many of your own posts, that exceeding the trailers GVWR is not very likely.---
Something can be "not very likely" but still be a "realistic possibility".
My data base of reported TV/TT weights contains 32 reports where both the trailer GVWR and the trailer GVW are known. These are for "loaded" trailers. Two of the 32 reports show GVWs which exceed the GVWR.
IMO, 2 out of 32 is not very likely. However, those two cases are not just "realistic possibilities" -- they're realistic actualities.
If someone is advocating using 100% of trailer GVWR as a "design load", why not use 110% or 120% or 150%. There's nothing magic about the 100% value, and most assume a higher value would be a "safer" value.
100% of GVWR does not establish the "worst case scenario".
A small minority of people knowingly or unknowingly exceed manufacturers' ratings. When we are dispensing loading advice should we assume every recipient is going to do the same?
Or, should we try to help them establish the most likely maximum value to which their trailer will be loaded?
Suppose someone has researched trailers and their first choice has a certified empty weight of 6000# and a GVWR of 9000#. They've done their homework and are quite confident their loaded trailer weight will not exceed 7500#. Their TV has sufficient capacity to tow a 7500# trailer without exceeding any ratings.
The problem with telling them they must assume the trailer will be loaded to its GVWR is that their TV cannot handle a 9000# trailer. Blindly following the "must assume 100% of GVWR" advice would deny them their first choice of trailer, even though the unused 1500# of CCC will have no effect whatsoever on the TV.
So, in effect, we're telling them it is better to tow a less-desireable trailer loaded to 7500# (100% of GVWR) versus towing their first-choice trailer loaded to 7500# (83% of GVWR). To me, that's backwards.