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Old 03-02-2019, 12:33 PM   #29
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Please allow me to qualify my previously posted comments on calculating tongue weight.

An LDH will change matters some. The gross combination weight will increase by the weight of the extra hitch hardware.

It's the balance, or axle weights that will change.

So in my basic, simple example posted previously, you need to weigh the combination without the LDH bars chained up if you wanted to know the accurate tongue weight.

However, knowing that is not the total pictre if you're pulling something large enough to require an LDH.

Adding an LDH in the mix is a bit more complicated than my basic example from earlier. But is still doable with the correct information from the Cat scale.

The main point to keep in mind is, no matter what your weights are, or how you transfer weight, the "moment" on each side, fore and aft, of the rear axle must be equal.

Dave
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Old 03-02-2019, 03:45 PM   #30
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Originally Posted by Metallicat View Post
I have a question that, based on my personal searches, hasn't been posted or discussed. The question has to do with tongue weight. Admittedly, I'm quite new to this world, but I've done extensive research and feel confident that I'd ace any written test. Now, since we all know that ideally you'd like your tongue weight to be 10-15% of gross trailer weight (or ACTUAL, loaded trailer weight), how does one actually go about obtaining this weight? I've seen many people post with the suggestion that they fall in that tongue weight sweet spot. But without a tongue weight scale......HOW?! I've researched tongue weight scales and I really don't want to come out of pocket for $150 for a product that will see very minimal use. Also, I don't actually see how to use a CAT scale to determine this, either. Thoughts from the smart people, please.

Maybe you can get some help from an owners manual.

https://www.dutchmen.com/rv-manuals-online
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Old 03-02-2019, 05:39 PM   #31
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I think you can come close with a CAT scale. It will take 2 weights. One with truck only then one with truck and trailer without a weight distribution hitch.

The truck's rear axle weight difference will be very close to the tongue weight.

It would be close enough for me.
2 weighs on the Cat will tell you what you need to know. First pass, loaded with everybody and every thing you plan to take camping, and hooked up like you go down the road. This will give you 4 numbers Steer, (Front axle of TV) Drive, (back axle of TV) Trailer, (weight on trailer axles) and Gross. (Total weight of combination)
Drop the trailer off out of the way, and pull back on, put the TV back where it was, and get a re-weigh. This will give you 3 numbers, Steer, Drive and Gross. Now you need a 3rd grader or a calculator. Gross with minus Gross without= Trailer weight. That Trailer weight minus the trailer axles will be the Tongue weight while going down the road.
Now some people say you need to weigh the whole rig with the spring bars lose, but what does that tell you? Does the TV squat when you take the bars loose? If not, you don't need WDH. If yes, than the tongue will be lower, and the higher the tongue, less it weighs.

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$20/$30 for all three weigh tickets and you have ALL the weights needed to figure Trucks GVWR, Truck/Trailer GCVWR, Affect of WDH, Tongue weight, Axle weights etc
A quick note on cost; First trip, pay full price. After that, tell them "re-weigh", give them the first ticket number, and the rest of your checks are discounted
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Old 03-02-2019, 07:20 PM   #32
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There will always be variations in measured tongue weight on dual axle trailers due to tongue height changes prior to measuring. The SAE addresses this in the j2807 towing standard.
“If a multi-axle trailer is used, it will be necessary to account for hysteresis in coupling load that results with coupling height change. Coupling height and load shall be measured for at least one cycle of height change. Hysteresis will likely increase with the magnitude of the cycle up to some magnitude of height change. The magnitude of the cycle shall, therefore, be at least this large with the mid-point of the cycle being the coupling height at which the handling tests are conducted. The coupling load is determined as the average of the maximum and minimum coupling loads at this coupling height that are defined by the hysteresis loop.”
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Old 03-03-2019, 07:51 AM   #33
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There will always be variations in measured tongue weight on dual axle trailers due to tongue height changes prior to measuring. The SAE addresses this in the j2807 towing standard.
“If a multi-axle trailer is used, it will be necessary to account for hysteresis in coupling load that results with coupling height change. Coupling height and load shall be measured for at least one cycle of height change. Hysteresis will likely increase with the magnitude of the cycle up to some magnitude of height change. The magnitude of the cycle shall, therefore, be at least this large with the mid-point of the cycle being the coupling height at which the handling tests are conducted. The coupling load is determined as the average of the maximum and minimum coupling loads at this coupling height that are defined by the hysteresis loop.”
Sorry, I thought this was a English language forum.
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Old 03-03-2019, 06:40 PM   #34
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Sorry, I thought this was a English language forum.
My thoughts too!!! But, after reading it out loud 3 times, I'm pretty sure I understand it. Even though I'm still very foggy on the "hysteresis loop."
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Old 03-04-2019, 03:16 AM   #35
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I think my first sentence sums it up pretty well.
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Old 03-04-2019, 04:59 AM   #36
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My thoughts too!!! But, after reading it out loud 3 times, I'm pretty sure I understand it. Even though I'm still very foggy on the "hysteresis loop."
Isn't that what happens when your wife tells her sister she saw a snake?

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I think my first sentence sums it up pretty well.
Don't get upset, it is common for people to be educated beyond my intelligence. You quote a rule that looks like it was written by somebody that was educated beyond their intelligence.
Moving on our roads the weight on tongue and tires will be constantly changing. We I can not measure or predict the changes. But with a scale, I can measure weights while not moving. And logic let's me see that with no other changes, raising the tongue it will transfer weight to trailer axle.
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Old 03-04-2019, 07:16 AM   #37
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Ok, a quick and dirty way (that may be a repeat of what somebody already said).


Weight of trailer not hooked up minus the weight of trailer hooked up equals tongue weight.
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Old 03-04-2019, 08:05 AM   #38
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Ok, a quick and dirty way (that may be a repeat of what somebody already said).


Weight of trailer not hooked up minus the weight of trailer hooked up equals tongue weight.
But how do you get the weight of the trailer hooked up? The CAT scale will tell you the weight on the trailer axles, but not the weight of the trailer.

So your quick and dirty would work only if by "Weight of trailer not hooked up" means the weight of the trailer axles and tongue jack sitting on one scale pad without the tow vehicle on the scale, and "weight of the trailer hooked up" means weight on the trailer axles with the combined truck and trailer sitting on the CAT scale.
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Old 03-04-2019, 08:49 AM   #39
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Is this possible on a CAT scale? Pull the trailer onto the cat scale to a point where the rear wheels of the tow vehicle are slightly off the scale platform. Weight the trailer hooked up. Unhook the coupler and raise the trailer just enough to take the weight off the ball. Bear in mind the tongue jack is on the scale platform. Weight the trailer "unhooked". Lower the tongue back onto the hitch ball and drive off the scale. Do the arithmetic from the two weights.
I used this method many times on equipment trailers at an inert landfill scale and it was simple and quick.
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Old 03-04-2019, 12:07 PM   #40
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Isn't that what happens when your wife tells her sister she saw a snake?



Don't get upset, it is common for people to be educated beyond my intelligence. You quote a rule that looks like it was written by somebody that was educated beyond their intelligence.
Moving on our roads the weight on tongue and tires will be constantly changing. We I can not measure or predict the changes. But with a scale, I can measure weights while not moving. And logic let's me see that with no other changes, raising the tongue it will transfer weight to trailer axle.
Certainly not upset
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Old 03-04-2019, 01:00 PM   #41
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Is this possible on a CAT scale?
Yes. That's basically rewording of my reply in post #38 above.

The point is to not confuse trailer weight with weight on the trailer axles.
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Old 03-04-2019, 01:25 PM   #42
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Originally Posted by ScoobyDoo View Post
Isn't that what happens when your wife tells her sister she saw a snake?



Don't get upset, it is common for people to be educated beyond my intelligence. You quote a rule that looks like it was written by somebody that was educated beyond their intelligence.
Moving on our roads the weight on tongue and tires will be constantly changing. We I can not measure or predict the changes. But with a scale, I can measure weights while not moving. And logic let's me see that with no other changes, raising the tongue it will transfer weight to trailer axle.
You are correct that raising the tongue will change the TW and you will reach a point where the TW stops changing. Same thing with lowering the tongue you will reach a point where TW stops changing. The high point where it stops changing and the low point where it stops changing, that span is the hysteresis loop.
So here’s how it works if you lower the tongue to the low end of the loop then raise it enough to sit on the ball you will get XXX for TW. Now raise the tongue to the high end of the span then sit it down on the ball, you will get YYY for TW. The variation will depend on the trailer but it can be quite different between the two.
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