WDH - I think I understand

[TheGreatWaz00]

OK a WDH distributes the hitch weight across three points (theoretically) - Front axle back axle, TT axle as opposed to simply at the hitch point.

So for simple math a hitch weight of 900# would DISTRIBUTE that 900# across the 3 axles 300/300/300 in a perfect world.

If my understanding is correct, the total downward pressure exerted by the hitch weigh is spread across the 3 axles. So would that mean only 600# (in my example) count against my payload amount since 300# is distributed back onto the TT axle?

Happy Trails!

[gijoecam]

sch911 wrote:
Weight is distributed across both of the tow vehicle axles, nothing much changes on the TT axles.

All of the hitch weight still goes on the tow vehicle. So you still add the full hitch weight to the tow vehicle. GVWR - Actual weight of tow vehicle = What you can carry.

Incorrect. Generally-speaking, with your typical 30-foot travel trailer, and most pickups, you will get a dead tongue weight distribution of roughly 1/3 on the trailer, 2/3 on the tow vehicle using a weight distributing hitch. Obviously everyone's rig is unique, and your mileage may vary, but that's a decent approximation for a lot of the rigs out there.

So, generally-speaking, if you have a 900lb tongue weight, when it's all said-and-done and adjusted, you will be bearing approximately 2/3 of the tongue weight across the tow vehicle's axles, and the remaining 1/3 will be borne by the trailer's axles.

Many of us have actual scaled weights to show the weight transfer. I'd be happy to share my numbers with you to let you do the math if you think it would help you understand the physics involved.

Ultimately, what APT wrote is a spot-on assessment of how they work and what happens.

[Dog_Trainer]

TheGreatWaz00 wrote:
Dog Trainer

No I am not going from thread to thread trying to justify pulling a TT with and under rated TV, and your comment is insulting to those of us on the forum who are newbies and ask lots of questions of those who have done this before. YES I ask lots of questions so I can fully UNDERSTAND what I am getting myself into.

Towing weight is along the X axis. Weight is along the Y axis and needs to be distributed. Two very different actions occurring and I am trying to understand every aspect of it before I make a well informed decision.

So please let me ask my questions without judgement, and thank you for your input.

Sorry I did not mean to insult you please seek all the information you need then go buy a truck that will pull what you want. I was simply pointing out that the truck in your other posts will not adequately pull the TT you have posted about.

[lbrjet]

Waz, read and understand what APT wrote and then you can make an informed decision.

[TheGreatWaz00]

Dog Trainer

No I am not going from thread to thread trying to justify pulling a TT with and under rated TV, and your comment is insulting to those of us on the forum who are newbies and ask lots of questions of those who have done this before. YES I ask lots of questions so I can fully UNDERSTAND what I am getting myself into.

Towing weight is along the X axis. Weight is along the Y axis and needs to be distributed. Two very different actions occurring and I am trying to understand every aspect of it before I make a well informed decision.

So please let me ask my questions without judgement, and thank you for your input.

[Dog_Trainer]

OP I think you are going from thread to thread trying to justify pulling a TT with an under rated TV. A properly adjusted WDH will give you a good tow experience and properly distribute the weight for that best experience. Go to the thread which gives you the proper set up procedure and follow it. In one of your posts you talk about a carrying capacity of under 1300lbs a WDH no matter how it is adjusted will increase that capacity it will do as noted and re distribute that weight. No matter how it is re distributed it will not change by much the amount of weight being carried by the TV.

[mosseater]

gmw photos wrote:
The scales tell the story. Example, on my travel trailer ( funfinder 189FDS ) and truck ( Nissan Frontier ) combo, I have 600 pounds of tongue weight. When the WD bars are tensioned, I am distributing 300 pounds to the front axle of the truck, and 140 to the trailer axles.
I can post a pic of the scale tickets if that would help visualize it.

Stole my lightning. I was going to say there isn't anthing "theoretical" about it. I have the weight slips to prove it, and you can't cheat physics. When one snaps up the brackets, that tension is carried between the points of the trailer axles and the hitch ball. There is no way around some of that weight being transfered to the trailer axles. No different than hanging a weight in the exact same spot

[gmw_photos]

The scales tell the story. Example, on my travel trailer ( funfinder 189FDS ) and truck ( Nissan Frontier ) combo, I have 600 pounds of tongue weight. When the WD bars are tensioned, I am distributing 300 pounds to the front axle of the truck, and 140 to the trailer axles.
I can post a pic of the scale tickets if that would help visualize it.

[BarneyS]

sch911 wrote:

BarneyS wrote:
What you have written is incorrect.

No not really! Perhaps I could have been more specific. But definitely not incorrect as you say. The weight is distributed to the tow vehicle differently. Not all on the rear axle. But nothing happens to the TT axles. And more importantly all of the TT's tongue weight is still resting on the tow vehicle, and must be considered in the payload calculations.

BTW: It has been part of my job to understand and determine such things!

I am sorry to say that, if you did your job according to what you have posted here, your results would have been skewed in the wrong direction. Your statement quoted above is still in error.

When you lift up the WD bars, via the chains and snap-up brackets which are attached to the trailer A frame, where do you think the force that results from lifting those chains/bars goes?

The downward force on the A frame, through the Snap-ups, is moved to the trailer axles which are the next part attached to the ground. There is no where else for that force to go.

I suggest, once again, that you take a long look at the first post in this thread for an understanding of how a WD hitch works.
Barney

[LarryJM]

sch911 wrote:

BarneyS wrote:
What you have written is incorrect.

No not really! Perhaps I could have been more specific. But definitely not incorrect as you say. The weight is distributed to the tow vehicle differently. Not all on the rear axle. But nothing happens to the TT axles. And more importantly all of the TT's tongue weight is still resting on the tow vehicle, and must be considered in the payload calculations.

BTW: It has been part of my job to understand and determine such things!

Yes you really ARE INCORRECT ... you apparently do not understand how a WDH works. It distributes the dead tongue wt (i.e. what you would see as TW on something like a Sherline scale) between the axles on both the TV AND the Trailer.

Larry

[jmtandem]

BarneyS wrote:

What you have written is incorrect.


No not really! Perhaps I could have been more specific. But definitely not incorrect as you say. The weight is distributed to the tow vehicle differently. Not all on the rear axle. But nothing happens to the TT axles. And more importantly all of the TT's tongue weight is still resting on the tow vehicle, and must be considered in the payload calculations.

BTW: It has been part of my job to understand and determine such things!



Barney is correct. If you understand how a weight distribution hitch works it has to add weight to the trailer axles when tensioned. The hitch redistributes tongue weight to both the front axle and the trailer axles. To see this redistribution of weight go to the scales and watch the axle weights (including the trailer axles) change as the hitch is tensioned.

[Sport45]

With enough spring bar you could lift the rear TV tires off the ground. Anyone else remember the commercial that featured a small car with no rear wheels pulling a trailer around? It was when small front wheel drive cars were pretty new in the USA.

[lbrjet]

The WDH works exactly as APT described.

[APT]

TheGreatWaz00 wrote:
So for simple math a hitch weight of 900# would DISTRIBUTE that 900# across the 3 axles 300/300/300 in a perfect world.

No. The purpose a a WDH is restore weight that is taken off the front axle by distributing some weight from the rear axle. A smaller amount is put on the TT axles.

For example using your 900 pounds of TW. If you just put the tongue on the ball, this would be the typical weights over nothing hitched:

TV front axle decreases by 300 pounds
TV rear axle increases by 1200 pounds
Net of 900 TW

Many WD systems and tow vehicle manuals recommend 100% front axle weight restoration. If you were to do this with typical vehicles today, these would be your weights compared to unhitched.

TV front axle same as unhitched
TV rear axle increased by 700 pounds
trailer axles increased by 200 pounds

As you can see, the weigh on the rear axle is significantly decreased from just weight carrying as well as front/steer axle weight is restored.

The percentage of TW applied to the trailer axles is typically in the 20% range based on the wheelbases and rear overhangs of full sized pickups and SUVs.

[sch911]

BarneyS wrote:
What you have written is incorrect.

No not really! Perhaps I could have been more specific. But definitely not incorrect as you say. The weight is distributed to the tow vehicle differently. Not all on the rear axle. But nothing happens to the TT axles. And more importantly all of the TT's tongue weight is still resting on the tow vehicle, and must be considered in the payload calculations.

BTW: It has been part of my job to understand and determine such things!