Tongue Weight Rating

I have to admit this is rather complicated when it comes to the bars and the actual TW. I have an example here that I'm still trying to decode. For my 2008 EXPY I took it to the scales and did some weight tests prior to going camping. It was fully loaded ready. The way I know to measure TW is to weigh the truck as is then hook up the trailer and weight it again. The difference should be your TW. However I noticed the TW is different when the bars are hooked vs not. So which TW would be the correct? In my case one of the weights is over the rated hitch while the other isn't. Again just based on net difference of TV weight before and after.

With bars TW = 794 Lbs
NO Bars TW = 926 Lbs

Scale values:

No Bars (KG):
Truck = 3510
Rear = 2140
Trailer Hooked = 2390

Bars (KG)
Truck = 3450
Rear = 1950
Trailer Hooked = 2460

Assuming the formulas are correct, and I have no reason to believe they are not, here’s my question.

I load my trailer, take it to the scales, and it weighs 10,000 lbs. For proper handling my tongue weight then needs to be between 1,300 and 1,500 lbs. I adjustment the load, use my portable scales, and the TW comes in at 1,400 lbs. Now I hook up my TT using a WDH. The tongue weight doesn’t change—it still weight 1,400 lbs.—but the net downward force on the ball is LESS THAN that number.

In other words, if I’m reading this right, the raw weight (downward force) of the tongue on the portable scales is not the same as the actual weight (downward force) on the ball with the WDH engaged.

So…am I still within the recommended TW range for safe towing?

myredracer wrote:
I think the harder thing to picture is what happens when the spring bars are hooked in place. In a way, it would *seem* like when you tighten up the chains, the tongue coupler gets pulled down onto the ball and therefore that the ball would get a higher vertical downward force which in turn would be transferred down to the ground.

But as you tighten up the chains, more of the weight of the rear of the truck (at the ball) is being suspended by the chains. This thus relieves some weight off the ball and rear axle of the truck. At the same time, due to leverage action, the chains pull down vertically on the A-frame transferring weight to the TT axles. Also at the same time, with the spring bars being pulled upward, there is a leverage action that tilts the front of the truck downwards thus transferring weight to the steer axle.

I'll offer a slightly different description of the process and include some example numbers to help put things in perspective.

When the lift chains are tensioned, they pull up on the WD bars and pull down on the trailer's A-frame.
The downward force on the A-frame is applied approximately 30" behind the ball.

Let's assume the distance from the ball to the midpoint between TT axles is 240".
Let's also assume the tension in each lift chain is 880#.

Since the point of application of lift-chain force is much closer to the ball than to the axles, a larger portion of the force will be carried on the ball.
In this case, the downward force on the ball is increased by 2*880*(240-30)/240 = 1540#.
The downward force on the TT's axles is increased by 2*880*30/240 = 220#.

Assuming a tongue weight of 1000#, the combined downward force on the hitch head is 1000+1540 = 2540#.
However, each WD bar is being pulled upward with a force of 880# for a total upward force of 1760# applied to the hitch head.
The resulting vertical force on the hitch head is 2540-1760 = 780#.
This is numerically equal to the TW minus the 220# which was transferred to the TT's axles.

The net effect on the hitch head is the same as exerting an upward force of 220#.
There also is a pitch-axis torque applied to the hitch head. For this example, the torque is 2*880#*30" = 52,800 lb-inch.
Assuming the upward force of 220# is applied 65" behind the TV's rear axle, the upward force generates an additional torque of 220#*65" = 14,300 lb-inch when using the TV's rear axle as a fulcrum.

Assuming a wheelbase of 130", the TV's front tires will react against the torque with an upward force of (52,800+14,300)/130 = 516#.
As a check, If we calculate the 220# added to the TT's axles multiplied by distance from TT's axles to TV's rear axle and then divide by TV's wheelbase, we get 220*(240+65)/130 = 516#.

The upward force of 880# applied to each WD bar has caused 220# to be transferred to the TT's axles and 516# to be transferred to the TV's front axle.
This means 220+516 = 736# has been removed from the rear axle.

If I am visualizing this correctly, there is therefore no net increase in weight of the coupler acting downward upon the ball. Structurally, the TV can handle the lower rating receiver rating without WDH engaged (say 500 lbs). Then when the WDH is engaged (with 1500 lb rating), there is no net additional downward force onto the ball itself and the receiver and TV does not actually "see" the additional 1000 lbs the tongue may be. Have I got this right at all, or am I out to lunch?

Application of WD does cause a significant increase in vertical force between coupler and ball.
However, the upward force from the WD bars (acting upward under the ball) causes the net vertical load on the hitch head to be reduced by an amount equal to the load which is transferred to the TT's axles.
The net load on the hitch head will be less than the tongue weight.

500# of tongue weight, without WD, will produce 500# of vertical load on the hitch head.
In my example above, the assumed 1000# of tongue weight, with WD applied, produced 780# of load on the hitch head.

When you go to a scale, the empirical data proves this to be true. It would be interesting to test this with some type of strain gauge or load cell.

The scales prove, within their accuracy, the load on the hitch head is reduced by an amount equal to the load which is transferred to the TT's axles.

Further to this discussion, I'm wondering what happens to weight transfer and weights/forces between coupler & ball when you use over or under-sized spring bars? Is there any difference in weight that the ball sees when the WDH is engaged? If you have say 1000 lbs of tongue weight, and only 800 lb bars, if you tightened the heck out of the bars to get enough weight onto the steer axle (if you even could), what happens? Same if you go the other way with over-sized bars and had say 1200 lb bars? Or does it even affect anything other than having a bouncier or harsher ride? Perhaps with too under-sized bars, there could be higher momentary up/down force between ball and coupler as you drive down the road? Could this possibly over-stress the receiver?

When using WD bars, if the rear of a TV goes through depression relative to the front tires and TT tires, the load on the WD bars will increase. This will cause increased loading of the coupler, ball, and hitch head.
Higher-rated (stiffer) bars will cause more load increase -- lower-rated bars will cause less load increase.

Normal driving down the road should not cause overstressing of a receiver.
VESC-5 specifies that the test torque (moment) for a 1000# tongue weight should be 114,200 lb-inch. This is more than double the WD-bar generated torque (which produced more than 100% of front axle load restoration) in my example above.

Ron

Have been following this thread and trying to digest differing sides of the discussion.

I can only see one definition of tongue weight, which is the portion of the weight of the trailer bearing down on the tongue.

Secondly, I can only see the weight of the WDH (less snap-up backets) as being part of the tow vehicle.

I don't think the age of the V-5 reg. matters and the basic definitions are still just as valid today. I'm not sure what is used in Canada.

In regards to adding a bike rack to the rear of a TV (I think that's what was meant), that is dead load added to the rear of the TV and counts as payload. Further (with risk of being smacked), I think it's a bad idea to load a TV aft of the drive axle.

I think some are having difficulty conceptualizing what is happening. If you had a 3' 2x2 length of tubing welded to and structurally attached to the rear of the TV and protruding out as far as a spring bar would, that'd be no different compared to a spring bar. Spring bars do not move vertically at the point they are attached to the TV.

I think the harder thing to picture is what happens when the spring bars are hooked in place. In a way, it would *seem* like when you tighten up the chains, the tongue coupler gets pulled down onto the ball and therefore that the ball would get a higher vertical downward force which in turn would be transferred down to the ground.

But as you tighten up the chains, more of the weight of the rear of the truck (at the ball) is being suspended by the chains. This thus relieves some weight off the ball and rear axle of the truck. At the same time, due to leverage action, the chains pull down vertically on the A-frame transferring weight to the TT axles. Also at the same time, with the spring bars being pulled upward, there is a leverage action that tilts the front of the truck downwards thus transferring weight to the steer axle.

If I am visualizing this correctly, there is therefore no net increase in weight of the coupler acting downward upon the ball. Structurally, the TV can handle the lower rating receiver rating without WDH engaged (say 500 lbs). Then when the WDH is engaged (with 1500 lb rating), there is no net additional downward force onto the ball itself and the receiver and TV does not actually "see" the additional 1000 lbs the tongue may be. Have I got this right at all, or am I out to lunch?

When you go to a scale, the empirical data proves this to be true. It would be interesting to test this with some type of strain gauge or load cell.

Further to this discussion, I'm wondering what happens to weight transfer and weights/forces between coupler & ball when you use over or under-sized spring bars? Is there any difference in weight that the ball sees when the WDH is engaged? If you have say 1000 lbs of tongue weight, and only 800 lb bars, if you tightened the heck out of the bars to get enough weight onto the steer axle (if you even could), what happens? Same if you go the other way with over-sized bars and had say 1200 lb bars? Or does it even affect anything other than having a bouncier or harsher ride? Perhaps with too under-sized bars, there could be higher momentary up/down force between ball and coupler as you drive down the road? Could this possibly over-stress the receiver?

waynec1957 wrote:

...
However, (as I understand it…and I could be wrong about this) the WDH does nothing to ease the force being applied to the fulcrum point by the weight in the bed of the truck.
...

hmmm, thought the WDH lifts any weight off the truck's rear axle.
Could be weight in the bed, really anywhere in the bed.
Could be weight transferred from the front axle by trailer tongue.
Could be actual tongue weight.
No?

Otherwise, like your explanation ...

waynec1957,

Great job on the summary.

You obviously don't need to have studied physics to understand that if you put a load on a scales, its weight will be registered.
And, if you put a load along side or under a scales, its weight will not be registered.

If we had a miniature scales to put between the ball and the coupler, it would be very easy to prove exactly what you're saying.
But, it shouldn't be necessary to prove it.

Ron

Both of you guys have obviously done a lot more research on this topic than I ever will and you both make good arguments. But for what it’s worth, considering my limited experience, here’s what I’m taking away from this.

When I load something into the bed of my truck, whether it’s 5 lbs. or 500 lbs., that weight is transferred to the ground first through the bed of the truck, through the frame, through the springs, to the axle and wheels, and ultimately to the ground. I can shift that weight around in the bed of the truck where the bulk of it is transferred by the back axle or I can move it forward where the weight is more evenly distributed between the front and rear axles. In either case, I haven’t placed an ounce of weight on my receiver. I can put that weight in the back of the truck (arranged however), crawl underneath, completely remove the receiver, and nothing about how the weight being transferred to the ground changes.

When I hook up my trailer using a ball and coupler setup the weight of tongue eventually gets transferred to the ground as well, but it takes a slightly different path. The weight is transferred through the hitch, through the frame, through the axles and wheels, and ultimately to the ground. The same thing happens (the same path is taken) when I insert my hitch into the receiver whether it’s a plain old 10 lb. hitch and ball or a 100 lb. WDH. Either way, the weight of the hitch starts on the receiver and is transferred to the ground.

Let’s say for instance I have 500 lbs. in the bed of the truck and 500 lbs. of weight on the receiver. There’s a net weight of 1,000 lbs being transferred to the ground…but 500 lbs. starts in the bed and 500 lbs. starts on the receiver. (Obviously what I’m talking about here ends up being payload)

If I take that entire 1,000 lbs and load it in the bed of the truck behind the rear axle I cause the rear axle to become a fulcrum point, but again, I haven’t applied an ounce of weight to the receiver. If I take that 1,000 lbs. and add it to the receiver the rear axle also becomes a fulcrum point but there’s not an ounce of weight being added to the bed of the truck. Likewise, if I put 500 lbs. in the bed of the truck behind the rear axle and another 500 lbs. on the receiver they both add up to 1,000 lbs. acting on a fulcrum point (the rear axle) but that weight originates from two different places.

Now…if I add a WDH to the equation (as I understand it) when I hook up my trailer a portion of that weight being applied to the receiver is distributed to the front axle of the truck and back to the axles on the trailer which eases the forces being applied to the fulcrum point (the rear axle). However, (as I understand it…and I could be wrong about this) the WDH does nothing to ease the force being applied to the fulcrum point by the weight in the bed of the truck.

It seems to me then the weight in the back of the TV (regardless how it’s loaded) is separate from tongue weight even though they both apply essentially the same forces to the TV. For instance, my class V receiver is rated at 1,500 lbs. tongue weight. I’m assuming (but don’t really know) that (somewhere along the line) is based on three things; (1) the construction of the receiver (how much stress it can handle), (2) how it’s attached to the TV, and (3) the towing capacity of the truck. In #1 & #2 how much weight I have in the back of the truck wouldn’t have any effect on the physical capacity of the receiver and in #3 we’re talking about the truck’s capabilities…not the receiver.

Keep in mind I never even took high school physics so I could be totally off base here, but after thinking it through this is what I came up with. Just my 2 cents….

Ron,

I guess you like I can read and interpret VESC-5 our own way, but I still and probably can't be convinced since it was written a VERY LONG TIME ago and had in my view an extremely limited applicability in assisting states in establishing minimum standards to improve safety of vehicles and their highways. You believe I think that tongue wt. is limited to that exerted by the trailer tongue on the ball and only consists of what we would normally measure by something like the Sherline scale inserted into the trailer tongue coupler. That might be fine for testing purposes such as VESC-5,however, I think when in real world applications it is any vertical force exerted at the point of the ball and both weight from above (i.e. the tongue of the trailer) or any other force primarily down at that point like the wt. components of a WDH/SWAY system for both a WC/WDH receiver mode or cargo behind the rear axle (in WDH mode) should count as tongue wt against the receiver tongue wt. ratings. I guess what I'm saying is that the trying to equate tongue wt. as used in a "TESTING DOCUMENT/SPECIFICTION" such as VESC-5 might not be directly applicable to real world conditions. I guess about the only argument I have for this is what e-trailer says about the wt. of the bike rack which is what should be considered as tongue wt. in the actual use of a system. You don't think that is a good analogy, but I do since as I previously stated I view that bike rack as all the extra wt of a WDH/SWAY system is analogus to the bike rack and the tongue wt from the trailer itself is analogus to the bikes ... i.e. the "LOAD". Thus my view of what we should think of tongue wt is more like I think what VESC-5 comment in their testing specs in Table 2 where they define "X" in their calculation as Hitch Rating for Maximum Vertical load on Hitch (lbs.)(Tongue Weight) This Vertical Load can also come from cargo wt. behind the rear axle whose component acts vertically in the plane thru the ball on the hitch. This force in addition to the WDH/SWAY system wt. and the Trailer tongue wt. are the three forces that the WDH system has to act upon and redistribute to the various axles. I just simply can't accept that things like all the variability of the different wts. of the WDH/SWAY systems and Cargo variability behind the rear axle like I showed in my case are basically "FREEBIES" when it comes to the tongue wt. ratings of my receiver and can be ignored ... that just doesn't pass the smell or gut test for me. I guess I've convinced myself that this view is sound and unfortunately as best as I can have listened to your views, but they haven't changed mine and probably never will.


I guess I will just have to leave it there and as I said will simply stand by my position and try to remember to put a caveat on it that there are other views and reference this thread for information.


Larry

LarryJM wrote:
This specifically says the hitch is "NORMALLY" mounted to the towing vehicle and part of the "PRIMARY CONNECTING SYSTEM" and one could I think argue that the WDH sway hitches as they are called are NOT NORMALLY mounted on the towing vehicle, but are added to the receiver temporarily when towing.---

This is simply a matter of definition. It should be clear by now that VESC-5 uses the word "hitch" to include the receiver among other components.

LarryJM wrote:
---Further more under section 3.9 all the components of what we normally consider a WDH and integrated Sway system such as the Reese SL, Equal-i-zer, and Blue Ox Sway Pro except for the ball and some minimal drawbar are clearly excluded specifically from the "Primary Connecting System" and thus are no part of the "HITCH" as used in VESC-5.

That is not correct. 3.9 does not exclude "all the components" 3.9 does not exclude the drawbar and it does not exclude the ball mount. 3.9 does not include WD bars, brackets, friction sway bars, etc because they are not part of the primary connecting system.

larryJM wrote:
I guess you could read it that way, but I consider my receiver a part of my vehicle towing Structural member since it's function to the transfer forces at the receiver to the vehicle frame. So again I read the hitch to be narrowly limited to only the ball and the balls support structure (i.e. minimalist drawbar) as defined previously in para 3.6 and 3.9 above.

Again, that's simply a matter of definition.
But, since your receiver transfers forces from the vehicle frame to your "hitch", your receiver is part of the system which connects the tow vehicle to the trailer.
Therefore, your receiver is part of the primary connecting system.

LarryJM wrote:
Based solely either on my lack of understanding or common sense I personally can subjectively see several components of these vertical loads as they comprise the tongue weight as defined in 5.4. --- These forces at the "ball/socket" in my view can come from 3 sources in the case of a weight carrying configuration ... the "dead trailer tongue wt", the weight of the WDH/Sway system in excess of a simple ball and mount, and the component of the cargo wt after the rear axle of the TV.

The vertical force at the "ball/socket", in my view, comes from one source -- the downward force exerted by the trailer tongue. There also is vertical upward force exerted on the ball mount via the WD bars.
The weight of the WDH/Sway system does not exert force on the "ball/socket". The weight of the WDH/Sway system is carried by the receiver.
TV cargo does not exert force on the "ball/socket" and it does not exert force on the receiver. The weight of TV cargo behind the rear axle is carried on the rear axle.

LarryJM wrote:
You made as I remember a comment about this cargo thing and when it's added or considered and I'm not sure that matters because in my view whatever wt. behind the rear axle that is acting as a lever on the TV to change the wt on the front axle the vertical component of that "CARGO WT" attributed at the ball/coupler location will be redistributed the same way as the additional wt. of just the trailer tongue. Thus to my way of thinking it is the same as tongue wt from a WDH standpoint as the tongue wt. at the trailer coupler.

Larry, you can define tongue weight any way you want to.
That doesn't change the fact that VESC-5 gives us a different definition of tongue weight and VESC-5 defines the procedure for determining a receiver's tongue weight rating.

Ron

LarryJM wrote:
Here is para 3.9 from the regulation you quoted excerpts from that I think are germane to your quote below and something I will refer to in my comments ....

"Primary Connecting System" means the combination of devices and their attaching structures that are normally utilized to maintain the connections between towing vehicles and trailer during towing operations. This includes, but is not limited to the ball-and-socket type of connection or draft means. NOTE: this does not include a safety chain, which is part of a secondary system normally utilized only upon failure of the primary connection, nor does it included weight distributing or sway control features or devices whose function is accessory to the maintenance of the towing vehicle-trailer connection

This seems to exclude all parts of either the WDH or Sway system such as the Sway bars, brackets, and sway hitch head.---

Larry, I think you completely missed the point of defining the "Primary Connecting System". Please note that the definition also refers to the "secondary system".

The Primary Connecting System is comprised of the components which are the path for transmission of the towing load between tow vehicle and trailer. These components are: "receiver" or "hitch", "shank" or "drawbar" or "hitch bar", "ball mount" or "ball platform", and "ball". The Secondary System primarily is the safety chains.

There is no reason to include "sway bars" or "brackets" in the definition of "primary connecting system" because those items are not part of the path for transmission of towing load.
I'm not sure what you mean by "sway hitch head", but I assume it is similar to "ball mount" or "ball platform".

LarryJM wrote:
---It would only include as mentioned in para 3.6 below that you quoted the ball and it's supporting structure which I take to mean the "drawbar" in it's simpliest configuration. I.E. these massive multiple height, extended length drawbars could be considered necessary to support the WDH functions to position the ball properly and not really what is being defined as part of what VESC is defining as the "Primary Connecting System"

Since a "drawbar", of any kind, is part of the towing load transmission path, it certainly would be included as part of the primary connecting system.
It is covered in the part of the VESC definition which says, "combination of devices and their attaching structures that are normally utilized to maintain the connections between towing vehicles and trailer during towing operations".

You are not correct in saying the primary connecting system would only include "the ball and it's supporting structure. Para 3.6 says:

3.6 "Hitch" defined for specific uses under Section 3.6(a. and b. below), generally means that part of the primary connecting system normally mounted on the towing vehicle, including a ball-support platform and those components which are attached to the towing vehicle.

Please note that this says, "including". It does not say, "only".

LarryJM wrote:
---Of course we have no way to resolve this issue of TW rating of the receiver when used in WDH configuration and how it applies to VESC-5 since it appears that VESC-5 sort of ignored all the WDH stuff which as already noted was almost non existent back when this reg was written and revised 36 years ago.

The WD bars and brackets were not included in the definition of "Primary Connecting System" because they are not part of the primary connecting system.

You are wrong about "WDH stuff" being "almost non existent back when this reg was written and revised". The authors of VESC-5 were well aware of that weight distributing systems were being used.
Please take a look at

10.2 Table 2 HITCH TEST FORCES

.
You will see that the right half of the table pertains to

WEIGHT DISTRIBUTING HITCH

Finally, please go back and read the portion of the definition of Primary Connecting System which states:

NOTE: this does not include a safety chain, which is part of a secondary system normally utilized only upon failure of the primary connection, nor does it included weight distributing or sway control features or devices whose function is accessory to the maintenance of the towing vehicle-trailer connection.

Yes, the VESC-5 authors were well aware of the existence of WDH stuff.

Ron