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.

[BarneyS]

#20 Home Depot,
"Thing that amazes me is how I ever got trapped into it pages back.......I pull a darn FW!!!"


I think that is a RIOT!!! :B
You are sure right in your other statement though. You guys are really educating a bunch of people including me. Looks like a good comprehensive summary is well in the making. Keep it up guys! 🙂
Barney

[_20_Home_Depot]

If someone doesn't get lost and actually reads through this entire thread to this point, stop and think about how much more you know about a WD system and TT/TV dynamics than you did when you started reading this thread. Pretty amazing isn't it?!!! Thing that amazes me is how I ever got trapped into it pages back.......I pull a darn FW!!!

[thomas_malenich]

I love it! Looks great.

On Edit: Do you think 12% to 15% is too restrictive? How about a # to strive for?? Then again perhaps it is better left out.

[Ron_Gratz]

I would say the first two sentences are confusing. I understand what you are saying, but the percentages will be confusing to someone who knows little about WD hitches. ---

Tom, you're absolutely correct. I got a little carried away trying to make the point that the rear axle load increase actually is GREATER than the tongue load. What would you think of the following:

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.

--- The most common recommendation I've seen for travel trailers is 10%-15% ---

Tim, I agree that 13%-15% is too restrictive. How about the following:

Recommended tongue weight

for travel trailers

is from

10%

to 15%.

Ron

On edit: Tom, I didn't see your 1:33pm reply to Tim before I posted. However, unless we are prepared to expand this thread to a more detailed discussion of tongue weight, I think it would be better not to recommend a TW percentage range at all than to recommend a range which is too restrictive.

[thomas_malenich]

Tim, You are right. Most sources have published 10% to 15%. Sherline recommends 12% to 15% - not sure if that is the same source that you were thinking of. That said, most of the research that I have done suggests that it is better to be closer to 15% than to 10%. And I support that based on personal experience. Having a range that starts at 10% suggests that 10% is OK, but I think having that asks for a bit of trouble. I have been recommending 13% to 15%, but I would also agree with the 12% to 15% range.

[tluxon]

thomas malenich wrote:
...Recommended tongue weight is from 13% to 15%.

I've never seen this range published by any reputable source. The most common recommendation I've seen for travel trailers is 10%-15% and at least one instance of 12%-15%. Bill Bryant's book, "Trailers and Fifth Wheels Made Easy", says on page 6,

"Tongue weight for conventional trailers should be about 10-15% of the gross weight. Remember low tongue weight causes fish-tailing, and control problems."

Other than that, I really like where this is going.

[thomas_malenich]

Without a WD system, the TV's rear axle load could increase by as much as 150% of the TT's tongue weight depending on overhang and wheelbase. The front axle load could be decreased by as much as 50% of tongue weight. For most TV/TT combos, these axle load changes will make the TV 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.
_____________________________________________________________________
Critique of the above statement:

I would say the first two sentences are confusing. I understand what you are saying, but the percentages will be confusing to someone who knows little about WD hitches. I would be thinking to myself "How could my rear axle load increase by more than the tongue weight I am adding to it??" I also think the percentages are unnecessary.

I think it needs to be simplified. We are not writing this statement for ourselves but for the new members benefit.

I still like the second paragraph if you want to go back to that definition of what a WD system does. However I would simplify your first paragraph to read like this:

Without a WD system, the tow vehicle's rear axle load could significantly increase from the added 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.

I would consider adding the recommended tongue weight percentage range to the end of the second paragraph. Those percentages are very important.
So the whole thing would look like this:

Without a WD system, the tow vehicle's rear axle load could significantly increase from the added 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 13% to 15%.

[Ron_Gratz]

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.

This summary was developed by team effort and was posted on 9/2/2004. I think it does a very good job of explaining to New Member WHAT a WD system does (and does not). However, it does not explain WHY the tow vehicle might need to be able to more effectively handle the tongue weight. We could begin the summary with a statement of WHY as a lead-in to the WHAT. The following have been offered as statements of WHY:

"From Equal-i-zer: With ordinary ball-type hitches, most of the trailer tongue-weight gets carried on the back axle of the tow vehicle, often this raises the front end of the vehicle."
Critique of this statement:
1) It is not "most of" the load that gets carried on the back axle. The added load is MORE THAN 100% (perhaps 150%) of the hitch load.
2) The hitch load does not "often" raise the front end. It ALWAYS decreases front axle load and raises the front end.

"Hitch-Web quote: Many vehicles can't carry the full tongue weight of a given trailer, and need some of the tongue weight transferred through the frame and pushing down on the front wheels."
Critique of this statement:
1) Doesn't really explain what happens at the rear axle.

"but the reason people who read this forum are interested in WDH is because a heavy tongue weight has overloaded the rear TV axle (and underloaded the front)."
Critique of this statement:
1) "overloaded" and "underloaded" need to be explained.

"When the trailer tongue is connected to the ball of a receiver, the rear axle bears much of the tongue weight. This raises the front of the tow vehicle and lowers the front of the trailer. --- First, the decreased load on the front axle can cause a loss of steering control and braking difficulties. Secondly, The increased load on your rear axle may be enough to exceed that axle's weight rating. Thirdly, the increased load on your receiver may be enough to exceed the weight rating of the receiver."
Critique of this statement:
1) "ball of a

hitch

" would be more accurate.
2) It is not "much of" the load that gets carried on the back axle. The added load is MORE THAN 100% (perhaps 150%) of the hitch load.

"If your trailer’s ball/tounge weight is causing the back end of the vehicle to sag, a weight distributing hitch can be used to return the vehicle to its normal height. Consult your owner’s manual to determine if your vehicle is suited for a WD hitch. --- When you hook your TT to your TV, the TT’s ball/tongue weight on the hitch causes an increased load on the TV’s rear axle and a decreased load on the TV’s front axle this may also cause your trailer’s COG to be effected ."
Critique of this statement:
1) Raises a very good point -- maybe New Member does not need a WD system.
2) Another good point -- not all TV's are suited for a WD system.
3) Any effect on the COG would be very small. Reference to the COG probably would tend to confuse.

Considering the above, a statement of WHY and WHAT could be:

Without a WD system, the TV's rear axle load could increase by as much as 150% of the TT's tongue weight depending on overhang and wheelbase. The front axle load could be decreased by as much as 50% of tongue weight. For most TV/TT combos, these axle load changes will make the TV 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.

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

Comments??

Ron

[thomas_malenich]

WD hitch forces are not involved directly in TT sway dynamics because they are vertical forces. However, changes in TV axle loads can have a significant effect on TV/TT sway dynamics primarily due to changes in steering response. The vertical load on the tires determines how much horizontal force the tires can generate.
___________________________________________________________________

We can conclude that the WD hitch can be "indirectly" involved in TT sway dynamics, since the WD hitch is responsible for changes in TV axle loads.

[thomas_malenich]

Such confusion about loads resulting from mass versus loads resulting from other effects is the reason I am trying to avoid the use of the term "weight distribution" and its counterparts.
____________________________________________________________________


Ron,

I hear you. We all went through that a while back. I once suggested that we should consider not using the term "tongue weight" once the tongue is hooked to a TV and no longer supported by the tongue jack.

Unfortunately the manufacturers use words such as "weight distribution", and "distributes tongue weight", and "the rear axle bears much of the tongue weight". We can not fight them.

I feel that we can provide the best service to the new members using the ORF search, by providing a definition/summary consistent with the manufacturers, yet enlightening.

That is why I wrote my summary using a blend of manufacturers wording and our/my wording.

[Ron_Gratz]

--- With the application of a 2000# load 30" from the ball coupler (as in your example), it does move the center of gravity of the TT forward. ---

Ken, this statement is true if the 2000# LOAD results from placing some MASS weighing 2000# at that location. The statement is not true if the 2000# LOAD results from TENSION in the spring bar tensioners. The CG of the TT can be moved only by adding or removing mass or by moving some of the existing mass.

Such confusion about loads resulting from mass versus loads resulting from other effects is the reason I am trying to avoid the use of the term "weight distribution" and its counterparts. If one is told that a WD hitch "distributes weight", and if one knows that "redistributing weight" can result in a change in location of the CG, then it is not illogical to incorrectly conclude that application of a WD hitch can move the CG. The problem stems from inconsistent definitions.

I must assume that this should help eliminate sway to some degree, since sway is a function of the position of all of the loads on the trailer in front of and behind the TT axle. (The mechanics of sway don't separate the distribution of the trailer weight from any other load applied to the frame.) Is that true?

The mechanics of sway are determined primarily by horizontal forces on the TT. When a mass is accelerated horizontally, a horizontal force results. Weight, per se, is not involved directly because weight is a vertical force (that comment ought to precipitate another 150 posts). Weight on the TT tires indirectly influences TT sway because it, among other things, determines how much horizontal force the tires can generate.

WD hitch forces are not involved directly in TT sway dynamics because they are vertical forces. However, changes in TV axle loads can have a significant effect on TV/TT sway dynamics primarily due to changes in steering response. The vertical load on the tires determines how much horizontal force the tires can generate.

Is this any clearer or have I only added to the confusion?

Ron

[4runnerguy]

Ron-

Before I comment on your comment on my comment on your comment on . . . 🙂

I made a statement earlier that WDH by themselves do little to eliminate sway. But maybe they do. With the application of a 2000# load 30" from the ball coupler (as in your example), it does move the center of gravity of the TT forward. I must assume that this should help eliminate sway to some degree, since sway is a function of the position of all of the loads on the trailer in front of and behind the TT axle. (The mechanics of sway don't separate the distribution of the trailer weight from any other load applied to the frame.) Is that true?

I guess I should try to do more of my brainstorming in the light of day rather than the middle of the night as I sometimes do. I look back at some of my posts as less than clear and maybe contradictory. Sorry.

[Ron_Gratz]

--- You have previously defined Tongue Weight as: "Tongue Weight: That portion of the TT weight which is carried on the ball coupler as opposed to that carried on the axles". Using your own definition, once the WDH is hooked up the tongue weight must decrease since the weight on the rear axle has increased.

Hello Ken,

Thanks for your contributions to the thread.

My definition of "tongue weight", Tongue Weight and Hitch Load - What are they and how are they different?, differentiates between WEIGHT of the TT and EXTERNAL FORCES on the TT. The definition states:

"If the weight of the hitch assembly is neglected, tongue weight is numerically equivalent to hitch load when there are no forces other than the TT's weight acting on the TT. If there are other vertical forces acting, then the values will be different."

and

"An example of other forces are those imposed on the TT by a WD bar tensioner."

My whole objective in proposing different definitions for "tongue weight" and "hitch load" was to have a definition by which "tongue weight" does NOT change when the WD bars are tensioned. Tongue weight, by this definition and when expressed as a percentage, is a measure of the relative location of the TT's center of gravity. As such, tongue weight is an important consideration for determining sway stability.

By the way, I don't think we should push someone to use a WDH without a caveat regarding the suitability for their particular trailer and TV.

I fully agree. I had considered adding the words, "where appropriate", to my proposed response to New Member. I will edit that post to include those words.

Ron

[Batmovan]

Remember the K.I.S.S. method? These are newbies who just want some basic facts for the purpose of deciding on, hooking up and using a WD hitch. Maybe the generic tongue weight term is fine. However if we think tonge weight is core to the idea I suggest we define Tongue, Ball and Hitch weight. We could then expand each question using those terms. The question and answer idea is a good one Ron; it is simple and to the point. Like this thread? 😉

NM: Do I need a WD hitch?
SM: If your trailer’s ball/tounge weight is causing the back end of the vehicle to sag, a weight distributing hitch can be used to return the vehicle to its normal height. Consult your owner’s manual to determine if your vehicle is suited for a WD hitch.

NM: Why do I need a WD hitch?
SM: , When you hook your TT to your TV, the TT’s ball/tongue weight on the hitch causes an increased load on the TV’s rear axle and a decreased load on the TV’s front axle

this may also cause your trailer’s COG to be effected

.

NM: Why is that bad?
SM: The increased rear axle load might exceed that axle’s load rating. Perhaps more importantly, the decreased front axle load might cause diminished steering response and braking action

of both TV and TT.

NM: How does the WD hitch change that?
SM: The WD hitch

redistributes

the amount of load carried on each of the TV

and

TT axles. The
TV’s rear axle load is decreased and the TV’s front axle load and the TT’s axle(s) load are increased

thus helping in leveling the TV and TT

.

NM: I’ve heard you need a certain amount of tongue weight for sway stability. Does the WD hitch change the tongue weight?
SM: No, the tongue weight remains the same. The WD hitch simply changes the way the total weight of

the

TV and TT is carried by the TV and TT axles.

This is still my favorite.

Ron and I hitch up his trailer. The rear of the truck sits way low, the front is way high, and the front wheels don't steer or brake worth a darn 'cuz of this.

We stick a long pry bar into the back end of his truck frame and pull up hard. The rear rises and the front drops. I have Ron trot along holding that bar up as I drive...the truck drives really well now, but Ron is getting tired. He chains the bar to the trailer tongue so he can take a breather. This works OK on the straights, but is a big problem on curves. We figure out a pivot system for the point the bar attaches to the truck. It turns well, but is really bumpy. Ron's Mrs. says to use spring steel bars. Duh!...Why didn't we think of that? Ron and I, and his Mrs., just invented the weight distributing hitch.


Ken

[4runnerguy]

Oasis Bob-

Sorry, it was late at night when I wrote that. I should have been more specific. It is the 4Runner that advises against using the WDH. But I would check the minivan owners manual. Often unibody vehicles advise against using the WDH because of the stresses they place on the vehicle.