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Old 07-07-2014, 02:10 AM   #1
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Formula for calculating tongue weight?

Is there a formula for calculating tongue weight based on the actual weight of the cargo and water?

I'm wondering what percentage of the used portion of the "Net Carrying Capacity" should be added to the A/S published unladen hitch weight to arrive at a Tongue Weight. I need that figure to add to occupant and cargo weight in order to see how close I am to the max payload of my tow vehicle.

Also, should the hitch and weight distribution system weights be assigned to tow vehicle or to the trailer?

I'm also interested in how the weight distribution system setup might affect the payload calculations of the tow vehicle and the trailer? Is this actually important?

My 2013 International 19 has a "Hitch Weight (w/LP & w/o options, water & cargo)" of 550. A "Unit Base Weight w/LP & w/o options, water & cargo) of 3823. "Gross Vehicle Weight Rating" of 4500. "Net Carrying Capacity" of 677.

2013 Dodge RAM 1500 Outdoorsman Crew Cab 4x2. 1403 pound payload...max cargo and occupants (door sticker-not RAM website).
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Old 07-07-2014, 06:15 AM   #2
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Why have two threads about the same subject. The current discussion is here:

http://www.airforums.com/forums/f238...ts-121859.html
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Old 07-07-2014, 06:27 AM   #3
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Originally Posted by interstateflyer View Post
Is there a formula for calculating tongue weight based on the actual weight of the cargo and water?
Not that we can probably get ahold of. AS might have a computer model of these relationships? You would need to know where each of the loads rests on the frame.

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Originally Posted by interstateflyer View Post
I'm wondering what percentage of the used portion of the "Net Carrying Capacity" should be added to the A/S published unladen hitch weight to arrive at a Tongue Weight. I need that figure to add to occupant and cargo weight in order to see how close I am to the max payload of my tow vehicle.
Without an actual tongue weight I would assume that it is 15% of your GVWR. This number will likely increase if your water tank is located in-front of the axle, and is full of water. If you've actually weighed your tongue at 550 lbs. then I would divide 550/4500 = 12.2%. If you have a tongue scale you might try filling up the tank and loading up your cargo. I received a rude-awakening when I did that exercise.

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Originally Posted by interstateflyer View Post
Also, should the hitch and weight distribution system weights be assigned to tow vehicle or to the trailer?
I assign them to the tow vehicle. My assumption is that the majority of the parts are physically hanging from the TV's hitch receiver. Generally only brackets are mounted on the trailer. I'm using an Equalizer brand hitch. Other brands of hitches might need to be treated differently.

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Originally Posted by interstateflyer View Post
I'm also interested in how the weight distribution system setup might affect the payload calculations of the tow vehicle and the trailer? Is this actually important?
I don't think that it is important, but I'm not absolutely sure.
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Old 07-07-2014, 09:16 AM   #4
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This would be the same math that a pilot uses to calculate weight and balance for an aircraft. Arms and moments calculation. You would need the starting weight at the axles and tongue. Using a datum point (like the hitch) measure from that point to each spot where you are adding weight. Then do a bunch of math to get close to the weight shift addition. Frankly not worth the effort for all of the different ways you can load a trailer. Better to take it to a CAT scale.
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Old 07-07-2014, 01:36 PM   #5
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I ordered a Sherline Trailer Tongue Weight Scale. This should take the mystery out of tongue weight calculation for various truck and trailer load combinations.
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Old 07-07-2014, 03:02 PM   #6
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I ordered a Sherline Trailer Tongue Weight Scale. This should take the mystery out of tongue weight calculation for various truck and trailer load combinations.
It has limited value. You need to weigh the truck (without Airstream) ready to camp at a truck scale. Then weigh the combination hooked up and ready to camp and weight distribution set, with the Airstream axles not on the scale. The difference is the payload the Airstream adds to the truck. It costs a lot less than a new scale and will give accurate payload results, which the Sherline scale alone cannot.

If you read the current thread referenced above in post #2 there is a good discussion about tongue weight and it's many variables.
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Old 07-07-2014, 03:39 PM   #7
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I intend to do what you describe. However I feel that there is value in knowing tongue weight when placing and distributing cargo in the trailer.

I've fine tuned my Reese weight distribution system for level riding and good handling so I don't want to change that.
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Old 07-07-2014, 03:42 PM   #8
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You can use a bathroom scale and a few boards to get your tongue weight. So load the coach as if it were ready for travel. Then weigh the tongue weight with a bathroom scale.
Look on the Internet, there are instructions on how to do it.
OR
Weigh the trailer alone at the scales.
Weigh the truck alone at the scales.
In both cases, they should be packed and ready for travel. You and all passengers should be in the TV when weighed.
Hitch the trailer to the truck. Then get the truck weighed on the scale, trailer not on the scale. The difference between the truck only weight and the truck with the trailer hitched is the tongue weight.
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Old 07-07-2014, 03:42 PM   #9
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Quote:
Originally Posted by interstateflyer View Post
I intend to do what you describe. However I feel that there is value in knowing tongue weight when placing and distributing cargo in the trailer.

I've fine tuned my Reese weight distribution system for level riding and good handling so I don't want to change that.
Yes, agree. I have a Shurline and use it as a quick pre-trip check when I've made significant changes to the load for that particular run. They are a good tool but have accuracy limitations.
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Old 07-07-2014, 04:54 PM   #10
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It's 110 miles round trip to the nearest CAT scale. I realize that the Shurline measures in 50 lb increments but it looks like a good place to start. Besides I can share with friends on rallies in exchange for beers.
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Old 07-07-2014, 05:20 PM   #11
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With that combo I wouldn't be too worried about the payload unless the Outdoorsman has worse payload than my Laramie.
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Old 07-07-2014, 05:30 PM   #12
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With that combo I wouldn't be too worried about the payload unless the Outdoorsman has worse payload than my Laramie.
This RAM's advertised payload is 1646. The door sticker says 1403. It's going to be close with my new camper shell.
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Old 07-07-2014, 05:32 PM   #13
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Ahh, I gotcha! Surprising how much those shells weight, I was going to get one myself, but opted to just stick with the flip bak.

Like you, the nearest scale is a hike and a half, thats why I started the other thread.
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Old 07-07-2014, 05:37 PM   #14
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You don't need a CAT scale for the process I described above.
Any truck stops near you?
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