WD hitch and cargo behind rear axle & tongue weight

I'll offer another opinion.

According to Reese, (and they have said this for at least the last 11 years I know of) Reese states that weight in the truck behind the rear axle is to be applied to the sizing of the WD bars.

This is a 4 meg Reese WD catalog file if you hit on it.

www.reeseprod.com/support/catalogs/Cequent-2015-06-Weight-Distribution.pdf

See the last page, page D-20 on the PDF.

Reese wrote:
The hitch weight formula for determining the load
which the hitch must carry:
HITCH WEIGHT* = TONGUE WEIGHT +
VEHICLE CARGO LOAD BEHIND REAR AXLE

OK, so that is what Reese has said for some time now. But, they do not describe to you how that actually works into the sizing of the WD bars. They leave it wide open for you to interpolate or just buy larger bars to cover any anticipated truck bed loads.

Now to the setup.

If you check your unhitched truck front fender heights or axle weights with the truck bed loaded and you hitch up and adjust the WD hitch to return the front end to unhitch height/weight, then the load on the WD bars is only from you adjusting the hitch.

OTOH If after you had adjusted the hitch as described above;

And you add extra weight to the truck bed behind the truck rear axle which is a large enough weight and or far enough behind the axle to lower the back of the truck, this can change the hitch head angle relationship to where it was originally adjusted to and add a level of tension to the WD bars. How much tension rise in the WD bar depends on how much the hitch head angle changed.

That is the only way I can figure (right now at least) why they feel you need to upsize the WD bars. If there are other ways, please point them out.

John

JBarca wrote:
OTOH If after you had adjusted the hitch as described above;

And you add extra weight to the truck bed behind the truck rear axle which is a large enough weight and or far enough behind the axle to lower the back of the truck, this can change the hitch head angle relationship to where it was originally adjusted to and add a level of tension to the WD bars. How much tension rise in the WD bar depends on how much the hitch head angle changed.

If the downward force exerted on the A-frame by the WD bars is increased, the load on the TT's axles will increase.
Since the weight of the trailer has not changed, and since the trailer axles now are carrying more load, the vertical load on the receiver must decrease by an amount equal to the load increase on the trailer axles.

That is the only way I can figure (right now at least) why they feel you need to upsize the WD bars. If there are other ways, please point them out.

I have no idea why they feel you need to upsize the WD bars. Perhaps they'll change this recommendation just as they have changed their recommendations for amount of front axle load restoration.

Ron

1. The WDH does in fact transfer a good % of the tongue weight, split to the front of the TV and the trailer axles. There is no magic number however, because the % transferred either direction differs among every set up WDH set up. More so, the length of trailer and TV wheelbase (different axle distances from the hitch) changes how much goes where. ONLY a scale will tell you exactly how much is transferred, and where it went.

2. While its good practice not to cheat the payload rating with the WDH, because actual weight is in fact transferred, you absolutely can use the WDH to work the payload rating in your favor. But again, there's no accurate math to work this out, you must used a scale to check Gross Weight, Gross Combined Weight and Axle ratings. Only the person towing can say if they feel ok doing this, as it is fact and legit, but it is not a recommended practice.

JBarca wrote:
I'll offer another opinion.

According to Reese, (and they have said this for at least the last 11 years I know of) Reese states that weight in the truck behind the rear axle is to be applied to the sizing of the WD bars.

This is a 4 meg Reese WD catalog file if you hit on it.

www.reeseprod.com/support/catalogs/Cequent-2015-06-Weight-Distribution.pdf

See the last page, page D-20 on the PDF.

Reese wrote:
The hitch weight formula for determining the load
which the hitch must carry:
HITCH WEIGHT* = TONGUE WEIGHT +
VEHICLE CARGO LOAD BEHIND REAR AXLE

OK, so that is what Reese has said for some time now. But, they do not describe to you how that actually works into the sizing of the WD bars. They leave it wide open for you to interpolate or just buy larger bars to cover any anticipated truck bed loads.

Now to the setup.

If you check your unhitched truck front fender heights or axle weights with the truck bed loaded and you hitch up and adjust the WD hitch to return the front end to unhitch height/weight, then the load on the WD bars is only from you adjusting the hitch.

OTOH If after you had adjusted the hitch as described above;

And you add extra weight to the truck bed behind the truck rear axle which is a large enough weight and or far enough behind the axle to lower the back of the truck, this can change the hitch head angle relationship to where it was originally adjusted to and add a level of tension to the WD bars. How much tension rise in the WD bar depends on how much the hitch head angle changed.

That is the only way I can figure (right now at least) why they feel you need to upsize the WD bars. If there are other ways, please point them out.

John

Thanks John for that input since now TWO MAJOR hitch manufacturers (Equal-i-zer and Reese) along with e-trailer have all confirmed what I have contended all along. Ron and I have disagreed on this before over the last several years with his "TRUMP CARD" being a decades old document defining tongue wt. as "THE AUTHORITY". All I can say is that what I have been advocating to me makes absolute sense and I guess one has to decide for themselves what should and shouldn't be included against the various tongue wt. ratings. While not critical most of the time it can make a difference in both receiver tongue wt. capacities along with proper sizing of WDH bars where many here advocate IMO cutting the size too close since they do not consider such items as the wt. of the WDH system itself or potential cargo behind the rear axle. However, IMO again WDH sizing is a two edged sword since unless you have "ENOUGH DOG" for your tail going too high of a WDH bar can result in a hasher ride on the more lightly suspensioned vehicles especially these 1/2T based TVs.

On this cargo subject it's probably more accurate that the wt. to be added is actually that seen "AT THE POINT OF THE BALL" so for example if the ball is 4' behind the rear axle and a 100lbs is added 2' (1/2 way) behind the rear axle then maybe only 50lbs should be added to the tongue wt. However, this really makes things complicated and why I think those advocating this simply assume any wt. behind the rear axle is at the point of the ball which would be the worst case which is what one should be using for safety reasons to begin with.

Larry

Ron Gratz wrote:

JBarca wrote:
OTOH If after you had adjusted the hitch as described above;

And you add extra weight to the truck bed behind the truck rear axle which is a large enough weight and or far enough behind the axle to lower the back of the truck, this can change the hitch head angle relationship to where it was originally adjusted to and add a level of tension to the WD bars. How much tension rise in the WD bar depends on how much the hitch head angle changed.

If the downward force exerted on the A-frame by the WD bars is increased, the load on the TT's axles will increase.
Since the weight of the trailer has not changed, and since the trailer axles now are carrying more load, the vertical load on the receiver must decrease by an amount equal to the load increase on the trailer axles.

Hi Ron,

I agree with you "if" there was weight added to the trailer A frame. That was not what I was saying or thinking. There is no weight change on the A frame. My thought was;

- The back of the truck was lowered by adding enough weight to truck bed (and the farthest back from center of the rear axle increases the moment)
- The added weight will compress the truck suspension to change the hitch head angle.
- The hitch head angle will tilt back the head (not a lot, but still be towards the TT)
- This head angle change will increase the WD bar tension for that point in time the weight was added
- The back of the truck will rise to create equilibrium once again but at a different lower vertical location.
- If the WD bar is sized larger, the drop effect will be less. (This is the only thing I can think of "why" they are saying this)


There will need to be enough weight change in the truck bed to practically affect this. A light suspension truck will have more affected then a heavier truck for the same amount of weight added.
Example 400# of oak firewood sitting right at the tail gate area. On a 1/2 ton truck that will cause a lot of truck drop ~ 2" - 3". On a 1 ton truck not so much but still movement ~ 1/2 to 1".

Ron Gratz wrote:

JBarca wrote:
That is the only way I can figure (right now at least) why they feel you need to upsize the WD bars. If there are other ways, please point them out.

I have no idea why they feel you need to upsize the WD bars. Perhaps they'll change this recommendation just as they have changed their recommendations for amount of front axle load restoration.

Ron

I agree, I am scratching my head on why they are trying to create a 1 size fits all recommendation. And they carry the same recommendation from a 600# WD bar to a 1,700# WD bar.

To me and my pee brain engineering mind, It seems that the common sense answer here is that the Hitch itself is rated by the manf. to carry a certain load. as example 500 tongue weight vs 1050 TW using a WDH. This is the amount of weight that the manufacture of the hitch attached to the frame of the truck is certified to carry. Nothing added to or subtracted from the bed of the truck will affect that certification.
Now along comes the WD hitch Manf. and he says to select the proper WD bars you must add the load behind the rear wheels to include all the weight that you need to redistribute. To me this is a value used to determine the size bars that you need for the WDH. It does not change the amount of weight that the Hitch is certified to carry as that weight is calculated by adding the weight added to the hitch receiver such as tongue weight + WDH weight.
I have never seen any warning by the OEM or hitch receiver manf. to the contrary that adds any caution to add the weight in the bed behind the rear wheels. Once again I think the confusion comes perhaps from the sizing of the WDH bars.

Well, I'm going to agree with Dog Trainer and LarryJM on this one, it's the only thing that makes sense. That was my original questions, how is the manufacture receiver rating affected by this added weight.
Yes, I do have a 1/2 ton truck however The F150 HD is a slightly different animal. 400 lbs. of firewood in the rear and I'd get very little squat. I never asked about the capability or overall payload capacity of my set-up, it's well within all limits, the question was only about the receiver limits and weight behind the rear axle. I'm good with the idea that this weight only affects the weight that needs to be transferred and has no bearing on the receiver limits.

LarryJM wrote:
---Ron and I have disagreed on this before over the last several years with his "TRUMP CARD" being a decades old document defining tongue wt. as "THE AUTHORITY".---

Larry, I define "tongue weight" as the downward force exerted by the coupler against the ball with the trailer level and no WD applied.

Can you please provide YOUR definition of "tongue weight", and explain how load in the bed of the TV changes the value of the tongue weight?

Ron

JBarca wrote:

Ron Gratz wrote:

JBarca wrote:
OTOH If after you had adjusted the hitch as described above;

And you add extra weight to the truck bed behind the truck rear axle which is a large enough weight and or far enough behind the axle to lower the back of the truck, this can change the hitch head angle relationship to where it was originally adjusted to and add a level of tension to the WD bars. How much tension rise in the WD bar depends on how much the hitch head angle changed.

If the downward force exerted on the A-frame by the WD bars is increased, the load on the TT's axles will increase.
Since the weight of the trailer has not changed, and since the trailer axles now are carrying more load, the vertical load on the receiver must decrease by an amount equal to the load increase on the trailer axles.

I agree with you "if" there was weight added to the trailer A frame. That was not what I was saying or thinking. There is no weight change on the A frame.---

John, there is no weight (mass) added to the A-frame. However, the tension rise in the WD bar does cause an increase in the downward force exerted against the A-frame by the WDH chains.
I was trying to point out that weight behind the TV's rear axle does not increase the downward force on the receiver.

My thought was;

- The back of the truck was lowered by adding enough weight to truck bed (and the farthest back from center of the rear axle increases the moment)
- The added weight will compress the truck suspension to change the hitch head angle.
- The hitch head angle will tilt back the head (not a lot, but still be towards the TT)
- This head angle change will increase the WD bar tension for that point in time the weight was added
- The back of the truck will rise to create equilibrium once again but at a different lower vertical location.
- If the WD bar is sized larger, the drop effect will be less.

I agree 100%.

IMO, if the added drop due to behind-the-axle weight is unacceptable, it is better to compensate for that added drop by using a rear suspension aid.
The problem with using the WDH to compensate for rear end drop due to bed load is that doing so will contribute to undesirable oversteer.

When load is added behind the TV's rear axle, load on the rear axle will increase and load on the front axle will decrease. This, by itself, will increase the tendency to understeer.
However, the behind-the-axle weight also causes the TV's center of gravity to move rearward. That makes the front tires more effective at steering and the rear tires are less effective. This, by itself, will increase the tendency to oversteer.
The two effects -- 1) changing the axle load distribution and 2) moving the CG -- tend to cancel each other.

If you then use the WDH to compensate for the effects of bed load, you are decreasing the rear axle load and are increasing the front axle load. This increases the tendency toward oversteer -- which is not a good thing when towing.

In the past few years, TV and WDH manufacturers have been specifying reductions in WDH load transfer based on directional stability considerations.
IMO, using more highly rated WD bars to achieve more load transfer is in direct conflict with the recent changes in Front Axle Load Restoration specifications.

It took some time for the WDH industry to make the FALR changes and, I guess, it'll take some more time for them to change their minds about using the WDH to compensate for bed load.

Ron

Ron Gratz wrote:

IMO, if the added drop due to behind-the-axle weight is unacceptable, it is better to compensate for that added drop by using a rear suspension aid.
The problem with using the WDH to compensate for rear end drop due to bed load is that doing so will contribute to undesirable oversteer.

When load is added behind the TV's rear axle, load on the rear axle will increase and load on the front axle will decrease. This, by itself, will increase the tendency to understeer.
However, the behind-the-axle weight also causes the TV's center of gravity to move rearward. That makes the front tires more effective at steering and the rear tires are less effective. This, by itself, will increase the tendency to oversteer.
The two effects -- 1) changing the axle load distribution and 2) moving the CG -- tend to cancel each other.

If you then use the WDH to compensate for the effects of bed load, you are decreasing the rear axle load and are increasing the front axle load. This increases the tendency toward oversteer -- which is not a good thing when towing.

In the past few years, TV and WDH manufacturers have been specifying reductions in WDH load transfer based on directional stability considerations.
IMO, using more highly rated WD bars to achieve more load transfer is in direct conflict with the recent changes in Front Axle Load Restoration specifications.

It took some time for the WDH industry to make the FALR changes and, I guess, it'll take some more time for them to change their minds about using the WDH to compensate for bed load.

Ron,

But doesn't the TW of the trailer also decrease the front axle weight while moving the TV center of gravity to the rear? By your logic, the under/over steer should cancel each other out and we wouldn't need a WDH is the first place.

It doesn't seem to make sense that 600# placed in the bed behind the rear axle has a different effect than 600# placed under the bed behind the rear axle.

I'm inclined to agree with Reese, Progress and eTrailer that behind the axle weight in the bed needs to be taken into account when selecting the right bars as some of that weight will be redistributed.

From a FALR perspective, it seems to me that 100% FALR number would be the load measured with my truck full of passengers, fuel and cargo in the bed in front of the rear axle but nothing in the behind the rear axle in the bed (or in the trunk! as I have a Honda Ridgeline ;)

Granted, in my particular case...I don't have enough payload left to really carry much in the bed or trunk given my trailer TW. So it doesn't matter to me. But for those with more payload...