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Open Roads Forum  >  Towing

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

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Ron Gratz

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Posted: 09/11/04 06:16am Link  |  Print  |  Notify Moderator

Quote:

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

sound beach, new york 11789

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Posted: 09/11/04 08:42am Link  |  Print  |  Notify Moderator

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%.



Thomas and Laura Malenich
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tluxon

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Posted: 09/11/04 10:24am Link  |  Print  |  Notify Moderator

Quote:

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.


Tim -
wife Beverly & 2 boys who love camping
2002 K2500 Suburban 8.1L 4.10 Prodigy
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Replaced 2000 Sunnybrook 26FK on 8/6/04



thomas malenich

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Posted: 09/11/04 12:33pm Link  |  Print  |  Notify Moderator

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.

Ron Gratz

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Posted: 09/11/04 12:36pm Link  |  Print  |  Notify Moderator

Quote:

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.

Quote:

--- 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.

* This post was edited 09/11/04 12:43pm by Ron Gratz *

thomas malenich

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Posted: 09/11/04 12:46pm Link  |  Print  |  Notify Moderator

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.

* This post was last edited 09/11/04 04:20pm by thomas malenich *   View edit history

#20 Home Depot

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Posted: 09/12/04 07:27am Link  |  Print  |  Notify Moderator

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!!!


#20 Home Depot
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BarneyS

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Posted: 09/12/04 10:50am Link  |  Print  |  Notify Moderator

#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!!!
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


2004 Sunnybrook Titan 30FKS TT
Hensley "Arrow" 1400# hitch
2002 Ford F250 Super Duty, 7.3L PSD
Visit our website here


Ron Gratz

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Posted: 09/12/04 08:32pm Link  |  Print  |  Notify Moderator

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.

Quote:

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.

thomas malenich

sound beach, new york 11789

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Posted: 09/12/04 09:37pm Link  |  Print  |  Notify Moderator

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.

* This post was last edited 09/14/04 10:40pm by thomas malenich *   View edit history

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