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Old 02-21-2013, 02:14 PM   #1
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WDH and tongue weight

The RAV has a 3,500 lb. tow limit, 350 lb. tongue weight limit.
My Hidden Hitch rates their receiver for the RAV at 4,000 lbs. / 400 lb. tongue weight.
I measured the tongue on my 17B and got 320 lbs. Then I weighed the WDH and got 64 lbs.
And that's were I got far beyond my mechanical and engineering experience.
One might assume that if you add 320 and 64 you would arrive at the tongue weight, but, since the WDH transfers weight to the front wheels of the tow and to the trailer axle, un-weighting the rear of the tow, what might be the actual tongue weight? And how would one figure that out?
And, if that's confusing; I'm confused.
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Old 02-21-2013, 02:34 PM   #2
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baglo

The WDB will distribute the tongue weight to the wheels of the tow vehicle and the trailer, in other words it will reduce the apparent tongue weight.

"A weight distribution system is important because it eases the situation by spreading some of that increased tongue weight off the rear axle of the tow vehicle and onto the front axle, as well as the axle (or axles) of the trailer.:
HowStuffWorks "Purpose of Towing Weight Distribution Systems"

You could confirm that by weighing the load on each axle of tow vehicle and trailer with and without WDB. I don't think you have a problem.
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Old 02-21-2013, 02:41 PM   #3
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I don't have a problem. I'm just bored, and started to wonder what the actual tongue weight would be so I weighed the trailer tongue and the WDH separately. Then it occurred to me that there was weight transfer, it's probably not as simple as adding the two weights.

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Old 02-21-2013, 03:59 PM   #4
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I do not know how you would measure the tongue weight with the WDH installed and the torsion bars loaded. As you know the purpose WDH is decrease tongue weight and level the tow vehicle and the trailer.
Weight Distribution Trailer Hitches Information Video | etrailer.com
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Old 02-21-2013, 04:16 PM   #5
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The only thing I could think of is to drive the rig over the scales with and without the hitch installed ( getting the axle weight for the rear of the tow ), but then the question, is that number relevant? And, what does it mean?

I think I'll vacuum the heat ducts..
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Old 02-21-2013, 05:03 PM   #6
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Lower tow vehicle rear axle weight with the WDH installed and properly adjusted would indicate that it working correctly.
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Old 02-21-2013, 05:19 PM   #7
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The tongue weight should include the WD hardware. Manufacturer's limits (for both tug and hitch) apply to the tongue weight, not the resulting load on anything after the WD spring bars are hooked up.

If you laid the spring bars on the tongue without hooking them up, you would have the situation to which the limits apply.

WD doesn't reduce tongue weight at all - it applies forces to make the tug's front axle and the trailer axle carry more, while the tug's rear axle carries less. You do that because of the high tongue weight. The WD's action actually greatly increases the load on the ball.
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Old 02-21-2013, 05:22 PM   #8
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I know it's working. Has been for five years on my set-up. But, what I'm getting at is that the WDH itself weighs 64 lbs. So when you insert it into the hitch receiver and add the trailer ( 320 lbs ), is the tongue weight now 384 lbs?
It shouldn't be. If the WDH is transferring weight from the rear axle, then it should be less.
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Old 02-21-2013, 05:27 PM   #9
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Quote:
Originally Posted by gbaglo View Post
The only thing I could think of is to drive the rig over the scales with and without the hitch installed ( getting the axle weight for the rear of the tow ), but then the question, is that number relevant? And, what does it mean?
Yes, the axle loads are relevant - they're the reason for using a WD system.
  • If the rear axle load without WD applied is too high, you have a reason for using WD.
  • After the WD system is applied, you need to ensure
    1. that you have not increased the front axle load too much (e.g. beyond what it was without the trailer at all, or in a really bad setup even beyond the front axle's rated capacity),
    2. that you have not overloaded the trailer axle, and
    3. that you have not reduced the rear axle load more than necessary (it needs load to have traction for control).
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Old 02-21-2013, 05:34 PM   #10
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I understand.
But, what is my tongue weight?
320# plus 64# or is it less because the WDH is employed?
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Old 02-21-2013, 05:37 PM   #11
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Quote:
Originally Posted by gbaglo View Post
I understand.
But, what is my tongue weight?
320# plus 64# or is it less because the WDH is employed?
Glenn - have you found a new hobby in retirement? The science of WDH's in relation to tongue weight!
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Old 02-21-2013, 05:38 PM   #12
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Quote:
Originally Posted by Brian B-P View Post

WD doesn't reduce tongue weight at all - it applies forces to make the tug's front axle and the trailer axle carry more, while the tug's rear axle carries less. You do that because of the high tongue weight. The WD's action actually greatly increases the load on the ball.
That's an interesting statement because the factory installed Class 3 hitch on my truck has the following stamped on it. Weight Carrying 350 lbs tongue 3500 lbs total, Weight Distributing 600 lbs tongue 6000 lbs total. Can anyone figure out why that is?

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Old 02-21-2013, 05:48 PM   #13
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Here is a source which might help. I haven't quite wrapped my mind around it yet:

RV.Net Open Roads Forum: Towing: Weight Distribution (WD) Hitch --- How it Works

According to this source, a WDH does not change the tongue weight. This contradicts my statement. I stand corrected.
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Old 02-21-2013, 06:00 PM   #14
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I just think of a WDH as a lever arm that is transferring forces - it raises the rear of the tow causing weight to be transferred to the front. When Reace installed ours he measured the height of the hitch off the ground without the trailer attached. Then he attached the WDH and adjusted it until the hitch was the same distance off the ground as it was without the trailer. So, to me, that would mean that the WDH was transferring weight off the hitch thereby making the "virtual" tongue weight less. (Phew, I need a beer after that, and maybe it is total BS)
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Old 02-21-2013, 06:06 PM   #15
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Glenn - have you found a new hobby in retirement? The science of WDH's in relation to tongue weight!
It's raining. It's cold. I have hemorrhoids...

Looked at the link. And, I still don't know if my tongue weight should include the weight of the WDH itself or not. I'm going to pretend not.

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Old 02-21-2013, 06:22 PM   #16
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The t/w is a function of the trailer, adding the t/w and w/d weight is a function of your tow vehicles carrying capacity. The w/d is like having a person lift up your rear end to shift weight to other axles. The weight is always there.
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Old 02-21-2013, 09:22 PM   #17
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Originally Posted by gbaglo View Post
I understand.
But, what is my tongue weight?
320# plus 64# or is it less because the WDH is employed?
320# plus 64#

... although once you start cranking on the vehicle structure with the WD spring bars, the exact value won't matter much, because the WD forces will be so large.
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Old 02-21-2013, 09:26 PM   #18
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You thought I was done, didn't you?
So, if the bars are 26# and the WDH is 38# and the trailer tongue is 320# then would the tongue weight be 320# plus 26# or 346#?
Not that it matters once the bars are deployed.
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Old 02-21-2013, 09:30 PM   #19
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Originally Posted by barry View Post
... the factory installed Class 3 hitch on my truck has the following stamped on it. Weight Carrying 350 lbs tongue 3500 lbs total, Weight Distributing 600 lbs tongue 6000 lbs total. Can anyone figure out why that is?
In weight-carrying mode, the rear of the hitch is being pulled down, and the front pried up in response. In weight-distributing mode the upward prying of the spring bars reduces the downward force on the rear of the hitch and pushes the front down, changing not just the magnitude but the direction of forces on the hitch structure. Since vehicles can handle more tongue weight when the WD system is used, hitch receivers are designed to handle more weight when the forces applied to them are in the directions of the WD mode.
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Old 02-21-2013, 09:40 PM   #20
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The w/d is like having a person lift up your rear end to shift weight to other axles.
Yes, although I'd say "the w/d is like having a person lift up your rear end, while standing on the trailer tongue, to shift weight to other axles".
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