Weight Distribution (WD) Hitch --- How it Works

[Ron_Gratz]

Edited 9/14/04: A summary of the 150+ posts in this topic has been developed by several of the contributors to explain WHY a weight distribution system might be necessary and WHAT a WD system does to improve a rig's handling:

Without a WD system, the tow vehicle's rear axle load could significantly increase due to leveraging of the tongue weight. Conversely the front axle load will be decreased. These axle load changes will make most tow vehicles unlevel. The decreased load on the front axle can cause a loss of steering control and braking difficulties. The increased rear axle load might exceed that axle's rating, and the load on the receiver might exceed its rating.

A weight distribution system enables a tow vehicle to more effectively handle the tongue weight of a trailer by removing some of the load from the tow vehicle's rear axle and distributing it to the tow vehicle's front axle and the trailer's axle(s). Note - When the WD system is engaged the actual tongue weight does not change. Recommended tongue weight is from 10% to 15%.

Consult your owner’s manual to determine if your vehicle is suited for a WD system.

Several recent posts have discussed WD hitches. One member stopped using his because he felt it was contributing to sway by decreasing the "tongue weight". I hope the following will give a better idea of what the WD hitch does and does not. Questions and comments are welcome.

Example assumptions:
TV wheelbase = 130”
TV rear axle to ball coupler = 65”
Ball coupler to TT axles = 200”
WD spring bar length = 30”
WD spring bar rear end load = 1000 lbs/bar = 2000 lbs total

How the WD hitch works:

Spring bar tensioner pulls UP on rear end of bar and DOWN on TT tongue. DOWN force of 2000 lbs on TT tongue adds a load of 300 lbs at TT axles.
This is calculated using ball coupler as the fulcrum: 2000x30/200 = 300.

Now, having added a load of 300 lbs at the TT axles, we must balance the TV/TT teeter totter. Using the TV’s rear axle as the fulcrum, to balance the 300 lbs at the TT’s axles we must add some load at the TV’s front axle.
The lever arm from the rear axle to front axle is 130”. The lever arm from the rear axle to the TT axles is 65+200 = 265”.
The required balancing load at the front axle is 300x265/130 = 611.54 lbs.

Or, we can calculate the reaction at the TV’s rear axle by treating the TV/TT as a lever with the fulcrum at the TV’s front axle.
The lever arm for the 300 lbs at the TT’s axles is 130+65+200 = 395”.
The lever arm for the rear axle is the wheelbase = 130”.
Since the TT axles are “lifting up” with a force of 300 lbs, this translates to an “uplift” at the rear axle equal to 300*395/130 = 911.54 lbs.

Summary of axle load changes:
TV front axle 611.54 lbs ADDED
TV rear axle 911.54 lbs REMOVED
TT axles 300.00 lbs ADDED

Now it is interesting to consider what happens at the hitch.

DOWN force of 2000 lbs on TT tongue adds a load of 1700 lbs at ball coupler.
This is calculated using TT axles as the fulcrum: 2000x170/200 = 1700.

The UP force of 2000 lbs on the rear ends of the spring bars produces an UP force of 2000 lbs at the hitch end of the spring bars.
The UP force of 2000 lbs minus the DOWN force of 1700 lbs on the ball gives a net UP force of 300 lbs at the hitch.
The vertical load on the receiver has been reduced by 300 lbs.
The vertical load transmitted through the ball has been increased by 1700 lbs.

It is interesting to note that TT weight and “tongue weight” do not enter into these calculations. The WD hitch does not distribute “tongue weight”. It simply removes load from the TV’s rear axle and distributes it to the TV’s front axle and the TT’s axles.

[capehorn]

Very interesting forum I have half the solution, use a SenZBar that would tell you what was happening at the tongue, I got one, but I dont use a weight distributing setup 😞

[thomas_malenich]

Thanks for your reply Ron,
I was coming around to the same conclusion. In studying my EQ it seems that the weight is centered around the ball and that it should be added to the tongue weight.

[Ron_Gratz]

I am still not sure about the weight of the WD hitch itself - would any of the 100#s be noticed in the rear axle load (after engagement)?
Would the full 100#s be used to reduce the hitch capacity in my example from 300#s to 200#s removed?

Tom,

The center of gravity of the WD hitch itself will be approximately under the ball. Therefore, the weight of the hitch simply can be added to the tongue weight when determining how much additional load is leveraged onto the TV's rear axle and removed from the front axle. For your example, the weight of the hitch would add 150# to the rear axle and remove 50# from the front.

In your example, the load on the receiver before WD would be 900# plus 100# for the hitch for a total of 1000#. This would be reduced to 700# when the WD bars are loaded to 2000#. The change in axle loads due to the WD hitch would remain the same.

Ron

[SpoiledRotten]

So now your going to pull the ole no point in continuing because......and do not want further confuse the issue routine.

After all of this, I bet neither one of you have got your weight distribution hitches set correct!!! :? :B

[BarneyS]

Ron,
I think it would be a good addition to the permanent threads at the top. The search engine would still find it and it would be available to new members to discover also. If we let it slide down the pages, it will only be available by search. I am not going to lock it either so you or others will still be able to post to it even if it is made sticky.

I just want to say one more thing about this thread.
It has been just about the most informative thread I have come across in all the forums. The thinking, effort, and cooperation that has occurred between you and the other members in the making of this thread has been outstanding. Congratulations to you and all the others for all your efforts. I will contact Admin and petition that this thread be made sticky at the top of the Towing Forum.
Thanks - all of you! 🙂
Barney

[thomas_malenich]

Tom,
If I saw a topic with this title, I would assume it pertained to why a tow vehicle is limited to carrying a certain amount. However, from your writeup, I assume you are talking about the contribution of tongue weight, hitch head weight, and weight distribution to load on the TV.

Rather than going through all the percentage calculations, it might suffice to say that, for estimatimg purposes, one can assume that a properly installed WD system can decrease the vertical load on the receiver by an amount equal to 1/3 of the hitch weight. However, one should always measure the actual weights for comparison with the TV and TT ratings.

Thanks Ron,
____________________________________________________________________

I did want to make a point of how much (in percentage) a WD hitch relieves the rear axle, hitch, and payload capacity.
I was not going to go through the percentage calculations - just use some of the results.

I am still not sure about the weight of the WD hitch itself - would any of the 100#s be noticed in the rear axle load (after engagement)?
Would the full 100#s be used to reduce the hitch capacity in my example from 300#s to 200#s removed?
I know that a Hensley would be added to the tongue weight, but not sure about an Equal-i-zer or Dual Cam hitch. Seems like they would not become a part of tongue weight, but rather would be primarily supported by the TV hitch.

[Ron_Gratz]

--- Is it time to petition Admin to make it sticky?
(after you make the edit :))
Barney

Barney,

It looks like the thread has run its course. I will edit the first post this evening if there are no additional inputs.

As for making it sticky -- I have mixed feelings about that. I tend not to read the new postings to the sticky topics. Because of the title, anyone doing a search for "weight distribution" will find the thread. Also, the thread is referenced in the FAQs.

Just my thoughts.

Ron

[Ron_Gratz]

I am thinking of starting a new thread and calling it "Understanding payload and GVWR limits".

Tom,
If I saw a topic with this title, I would assume it pertained to why a tow vehicle is limited to carrying a certain amount. However, from your writeup, I assume you are talking about the contribution of tongue weight, hitch head weight, and weight distribution to load on the TV.

Rather than going through all the percentage calculations, it might suffice to say that, for estimatimg purposes, one can assume that a properly installed WD system can decrease the vertical load on the receiver by an amount equal to 1/3 of the hitch weight. However, one should always measure the actual weights for comparison with the TV and TT ratings.

Ron

[BarneyS]

Ron, I like it as well! Congratulations on bringing this thread to a full circle.:) Is it time to petition Admin to make it sticky?
(after you make the edit :))
Barney

[thomas_malenich]

Ron, that summary really looks great. I might just frame it and hang it in the bathroom of our trailer.:W

[tluxon]

thomas malenich wrote:
I am thinking of starting a new thread and calling it "Understanding payload and GVWR limits".

Thomas, I think you have a great idea. One thing I would add is some detail related to those whose TT tires don't have a fully-inflated load rating that adds up to the TT's GVWR. It might help them figure out if they're overloading those tires when adding the load from a WD system.

All the best!

[tluxon]

Great job, Ron. I like the idea of putting that summary at the top of the thread in the first post. I think it's simple enough for most newbies to follow and accurate enough to avoid confusion.

[thomas_malenich]

I am thinking of starting a new thread and calling it "Understanding payload and GVWR limits".

A part of what I would discuss would incorporate some of what I have learned in this thread. I need everyones help to make sure that I use accurate percentages. I have used Ron's example to figure and extract the rough percentages that I would use.

Ron's initial example of:
TV wheelbase = 130”
TV rear axle to ball coupler = 65”
Ball coupler to TT axles = 200”
WD spring bar length = 30”
WD spring bar rear end load = 1000 lbs/bar = 2000 lbs total


I would like to now introduce a tongue weight(TW) of 900#s.

Before a WD hitch is engaged:
1. What is the increased load on the rear axle? Approx 1350#s or 150% of TW. The added weight is a combination of tongue weight and front end weight transferred to the rear.
2. What is the decreased load on the front axle? 450#s or 50% of TW.

After a WD hitch is engaged as per example above with a total of 2000#s of tension:

Summary of axle load changes from Ron :
TV front axle 611.54 lbs ADDED
TV rear axle 911.54 lbs REMOVED
TT axles 300.00 lbs ADDED


The WD hitch distributes 300#s or 33% to the TT axles, so the LOAD introduced to the TV is 600#s or 67%. Of this 600#s, 162#s is now on the front axle and 438#s remains on the rear axle. The front axle lost 450#s originally but now it is only increased by 162#s.
The load on the receiver has been reduced by 300#s.

The load on the rear axle was increased by 150% of TW before the WD hitch was engaged. Now the load on the rear axle is only about 50% of the TW.

Conclusion regarding payload: The TV needs 600#s of available payload (not 900#s), after it is loaded with passengers, gear, and fuel.

On edit:

I did not consider the weight of the hitch itself. Lets say the weight of the WD hitch is 100#s.

[Ron_Gratz]

I propose to place the following at the beginning of the initial post for this thread. If no additional suggestions for the summary are posted by 9/14, I will do the editing on that date.

Edited 9/14/04: A summary of the 150+ posts in this topic has been developed by several of the contributors to explain WHY a weight distribution system might be necessary and WHAT a WD system does to improve a rig's handling.

Without a WD system, the tow vehicle's rear axle load could significantly increase due to leveraging of the tongue weight. Conversely the front axle load will be decreased. These axle load changes will make most tow vehicles unlevel. The decreased load on the front axle can cause a loss of steering control and braking difficulties. The increased rear axle load might exceed that axle's rating, and the load on the receiver might exceed its rating.

A weight distribution system enables a tow vehicle to more effectively handle the tongue weight of a trailer by removing some of the load from the tow vehicle's rear axle and distributing it to the tow vehicle's front axle and the trailer's axle(s). Note - When the WD system is engaged the actual tongue weight does not change. Recommended tongue weight is from 10% to 15%.

Consult your owner’s manual to determine if your vehicle is suited for a WD system.

Ron

P.S. I pull a Ford Explorer.