WD Hitch Weight % Transferred

^^^^^^ ....uh.....ok, thanks Ron ! You have given me something think about this afternoon as I sit here and stare at the truck and hitch. I think it's going to take me a little while to wrap my head around all that. :D

gmw photos wrote:
---I have 600 pounds of tongue weight. When the trailer is just on the ball, with no weight distribution, my steer axle loses 300 pounds. I set my WD hitch to restore that 300 pounds to the steer axle, and in doing that, it also increases the load on the trailer axle by 140 pounds.---

Thanks for the numbers. It's good to see that your 23% of TW transferred to the TT axles agrees well with theory.

As others have stated, the vertical force on the ball remains 600 pounds.---

Perhaps you mean vertical force on the hitch?

With WD applied the vertical force on the ball becomes equal to the tongue weight
PLUS the downward force exerted on the A-frame by the two WD bars
MINUS the load transferred to the TT's axles.

In your case, the vertical force on the ball might be 600+1000-140 = 1460#.
The front ends of the WD bars would be pushing upward against the bottom of the hitch head with a force of 1000#.
The net downward force on the hitch then is 1460-1000 = 460# -- which is equal to the tongue weight MINUS the load transferred to the TT's axles.

So, with WD applied, the vertical force on the hitch (and the vertical load on the TV) is decreased by the amount of load transferred to the TT's axles.

Ron

The fairly simple relationship is: TW% = FALR% * D2/(D2+D3)

where TW% is percent of TW transferred to TT's axles
and FALR% is load restored to front axle divided by load removed from front axle.

For example, if D2 = 65", D3 = 195", and FALR% = 100%: TW% = 100% * 65(65+195) = 25%

For the above dimensions, if you wish to restore only 75% of front axle load, TW% is 18.75%.
If you wish to restore 125% of front axle load, the theoretical TW% is 31.25%.

Given the actual values for D2 and D3 and your desired FALR%, you can calculate your own value for the required percentage of TW transferred to the TT's axles.

The short answer to your question -- 20% is a pretty good rule of thumb.

Ron,

Thanks for the formula. I appreciate it.

To the OP, not sure if this is what you are asking, but as an example, this is what my numbers are for my camper. I have 600 pounds of tongue weight. When the trailer is just on the ball, with no weight distribution, my steer axle loses 300 pounds. I set my WD hitch to restore that 300 pounds to the steer axle, and in doing that, it also increases the load on the trailer axle by 140 pounds. So a total 440 pounds of tongue weight gets re-distributed.

As others have stated, the vertical force on the ball remains 600 pounds. Without WD I am effectively heavy in the "center" ( rear axle of the truck) of the combined rig. With WD I am more "balanced" because the action of the weight bars has effectively rotated the truck frame forward, as seen by the weight restoration on the steer axle. It has also rotated the trailer frame backward, again as seen by the increase in weight on the trailer axles.

xcntrk wrote:
Here's an example:

Your example shows, for no WD,
the steer axle lost 3200-3040 = 160# and
the drive axle gained 3880-2840 = 1040#.

With no WD, I would expect the steer axle to lose an amount equal to about 40-50% of the 880# TW and the drive to gain about 140-150% -- depending on TV wheelbase and ball overhang.
How did you calculate the front axle loss and the rear axle gain?

Also, the bottom line shows TW Redistributed = 14% w/WD.
How is that value calculated?

Ron

jmtandem wrote:
---The couple hundred pounds that the WD will redistibute to the TT axles is almost a moot point. As somebody else indicated, if 200 pounds one way or the other will make or break you, then you have too much trailer.

To put that 200# into perspective --
if your TV has a GVWR of 7000#, a GVW of 6800# is 97% of rating and a GVW of 7000# is 100% of rating.
Whether you tow at 97% or 100% of GVWR probably is moot.

However, IMO, the difference of having an allowable TW of 1000# versus 800# is not moot.
It might mean the difference of having an allowable TT weight of 8000# versus having an allowable TT weight of 6400#.

In the above example, you have two choices:
1) operate at 97% of GVWR with a 6400# loaded TT weight or
2) operate at 100% of GVWR with a 8000# loaded TT weight.

Those who feel it is okay to operate at 100% of the TV manufacturer's ratings might prefer to have the additional flexibility in choosing a TT.

Ron

Here's an example:





As Ron mentioned, there's 2 different sets of weight transferred. There's the exchange of weight between the front & rear axles of the TV, then there's the exchange of weight back to the TT axles. In the example above, 240lbs of tongue weight is moved from the rear axle back to the front, and 120lbs is moved from the rear axle back to the TT axles.

kgarrett9999 wrote:
Obviously, the answer to my question is going to depend, but what is a good rule of thumb to use when estimating how much weight a WD Hitch will transfer from the hitch?

You're correct -- it depends. It depends on:
distance from TV rear axle to ball (D2),
distance from ball to midpoint between TT's axles (D3),
and amount of Front Axle Load Restoration (FALR).

The fairly simple relationship is: TW% = FALR% * D2/(D2+D3)

where TW% is percent of TW transferred to TT's axles
and FALR% is load restored to front axle divided by load removed from front axle.

For example, if D2 = 65", D3 = 195", and FALR% = 100%: TW% = 100% * 65(65+195) = 25%

For the above dimensions, if you wish to restore only 75% of front axle load, TW% is 18.75%.
If you wish to restore 125% of front axle load, the theoretical TW% is 31.25%.

Given the actual values for D2 and D3 and your desired FALR%, you can calculate your own value for the required percentage of TW transferred to the TT's axles.

The short answer to your question -- 20% is a pretty good rule of thumb.

Ron

Obviously, the answer to my question is going to depend, but what is a good rule of thumb to use when estimating how much weight a WD Hitch will transfer from the hitch?

Another thread recently suggested an estimate of 20-25%.

More data would help. What is the gross weight of the trailer? What tow vehicle and how many people, dogs, bbq's, firewood, bicycles, kayaks, etc do you also plan to take along? What does the truck weight empty at the scales, not brochure weights, and what is the gross weight of the truck per the manufacturer? Then we can provide more help.

Generally a WD hitch properly tensioned will place about 20-25 percent of the redistributed tongue weight back to the TT axles, the rest stays with the truck (tow vehicle plus the weight of the hitch that you might want to estimate at 100 pounds). The hitch weight plus tongue weight that remains with the tow vehicle is a direct deduct from tow vehicle payload and axle loading ratings. In most cases the front axle should be loaded to about what it was before the tongue weight was added, but not always and in some cases the manufacturers are suggesting only a fifty percent increase of the weight taken off. I know of no manufacturer that suggests adding back more weight than was taken off. The best way to determine this is to go to the scales and weigh everything and also use a tongue scale as well.

As a rule of thumb use 13 percent of the trailer's gross weight you are looking to purchase as the tongue weight. For example a 7500 pound trailer will have a tongue weight almost 1000 pounds plus about another hundred pounds for the hitch or around 1100 pounds. That is a lot of trailer weight for a tow vehicle that has 1450 pounds of total payload available. The couple hundred pounds that the WD will redistibute to the TT axles is almost a moot point. As somebody else indicated, if 200 pounds one way or the other will make or break you, then you have too much trailer.

The hitch still sees the full TW. In Ron's terms the amount of vertical load on the hitch and tow vehicle axles is reduced by about some amount. I say about 20% when the front axle is load is restored to unhitched amount. However, some vehicle manufacturers are suggesting restoring only 50% of the weight lost on the front axle when using a WDH. This will mean the rear axle is more heavily loaded and less transferred back to the trailer axles.

Example:
1000 pounds of TW
ball on hitch means about 1400 pounds increase to rear axle weight, 400 pound decrease on front axle
WDH with front axle weight 100% restored would mean rear axle bears 800 pounds (instead of 1400) and TT axles bear an additional 200 pounds.

WDH with 50% front load restored means front axle loses 200 pounds, rear axle gains 1100, TT gains 100. So net on TV axles is 90% of TW.

IMHO, if you are concerned about 200 pounds, buy a much smaller TT or larger TV. Otherwise, there are many people who end up over at least one of their TV's ratings and travel safely to their destination.