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Old 09-18-2020, 10:07 PM   #1
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Hensley Tongue weight experiment

I had a some spare time before we started our trip to the local state park last week and I weighed the tongue of our trailer. I have seen this method several times in our trailer manual and have always wanted to try it out of curiosity.
- Trailer is 1994 Classic 30 with a factory tongue weight of 750 lbs.
One modifications is the batteries have been moved from inside the trailer to a heavy metal case on the trailer tongue. These are Deka deep cycle lead acid group 31 @ 60 lbs each.
1 propane tank is full and I would guess the other to be closer to 3/4. The trailer was stocked with groceries and clothes. The fresh water tank was empty but this shouldn't matter because the tank is located between the trailer axles. I typically have it full for a trip.
I used the bathroom scale method as described in the Airstream manual and came up with 855 lbs. I placed the hydraulic jack under the stinger where it would be held by the trucks receiver and zeroed out the bathroom scale to account for the weight of the jack. I placed a couple sets of vice grips to keep the Hensley hitch stable and the spring bar jacks had to be tightened down some to keep the stinger level. From there I just used the hydraulic jack until I saw the trailer jack move from its foot.
Think this method is accurate enough?
I have weighed the trailer in the past and there is typically 7400 lbs on the axles and we camp with about the same amount of stuff each time so it should be close enough for this experiment.
So then what is the correct percentage:
855/7400 = 11.5% tongue weight divided by axle weight
or would it be
855/8255 - 10.3% tongue weight divided by total weight

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Steve, Christy, Anna and Phoebe (Border Collie)
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2009 Dodge 2500, 6 Speed Auto, CTD, Quad Cab, Short Bed
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Old 09-19-2020, 07:41 AM   #2
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Tongue weight percentage is figured by dividing the tongue weight by the total weight of the trailer with WD bars NOT attached.
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Old 09-19-2020, 08:44 AM   #3
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First off...some terminology issues. Tongue weight is measured at the ball and is a spec required/determined from a trailer manufacturer standpoint. Your exercise is measuring TV receiver weight, and is required/determined from a TV manufacturer standpoint.
The two weights are significantly different values.
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Old 09-19-2020, 09:02 AM   #4
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Quote:
Originally Posted by dznf0g View Post
First off...some terminology issues. Tongue weight is measured at the ball and is a spec required/determined from a trailer manufacturer standpoint. Your exercise is measuring TV receiver weight, and is required/determined from a TV manufacturer standpoint.
The two weights are significantly different values.
Thank you Rich, I was here earlier this morning but didn't want to make the same observation I've blabbering for years.
TW is NOT the same as receiver weight.

Bob
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Old 09-19-2020, 09:07 AM   #5
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Following- Thanks for this thread chrispyboy.

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Old 09-19-2020, 09:09 AM   #6
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As rich indicates your scale is maybe 18 inches from the pitch articulation point where the load of the trailer is actually being supported so your tongue weight is likely 80-150 lb off. Also if there is any tension on the WD bars and I think there must be to support the pitch point, that will also cause additional significant underweight. You need to catch the weight on the trailer side of the tension bars at the pitch point.
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Old 09-20-2020, 03:50 AM   #7
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I never thought about the difference in tongue weight and receiver weight. I was only curious about tongue weight and how it relates to the WD bars. I guess the receiver weight will tell me that weight is within the window of the class 4 receiver on the truck. I think dead weight on the class 4 receiver is 1000 lbs max and 1,200 with a WD hitch in use.
So to get the actual tongue weight should the scale be under the trailer ball?
All this brings me to another question about picking the correct WD bars. Which weight should be used in sizing the bars correctly? Which weight is more relevant?
Currently using 1000 lb bars. These seem to be doing the job but they do get cranked up tightly.
And yes for this experiment the WD bars were tightened only enough to keep the stinger level.
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Steve, Christy, Anna and Phoebe (Border Collie)
1994 Classic 30'11" Excella - rear twin
2009 Dodge 2500, 6 Speed Auto, CTD, Quad Cab, Short Bed
Hensley Arrow hitch with adjustable stinger
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Old 09-20-2020, 06:00 AM   #8
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We use a Hensley, I started with 1400lb bars.
After weighing and getting the actual weight that needed to be moved I got a better designed receiver, (longer moment arms to improve WD leverage) and dropped down to 1000lb bars.

The numbers....

1200lb TW on a Sherline scale 4" forward of the ball.

760lb off the TV front axle with no WD and a loaded for camping rig.
560lb returned to the FA with WD set, 200lb light.
AS axles 7480lb with no WD, 7640lb with WD, 160lb moved.
560+160=720lb total weight moved. with 1000lb bars.

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"cranking up tight" moves weight.
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Old 09-20-2020, 07:09 AM   #9
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Quote:
Originally Posted by crispyboy View Post
I never thought about the difference in tongue weight and receiver weight. I was only curious about tongue weight and how it relates to the WD bars. I guess the receiver weight will tell me that weight is within the window of the class 4 receiver on the truck.

I think dead weight on the class 4 receiver is 1000 lbs max and 1,200 with a WD hitch in use.
Actually, no because the advertised weights are expressed as common coupler weights assuming a standard size shank and ball assembly.

Quote:
So to get the actual tongue weight should the scale be under the trailer ball?
Bob's photos addressed this I hope.

Quote:
All this brings me to another question about picking the correct WD bars. Which weight should be used in sizing the bars correctly? Which weight is more relevant?
The typical loaded trailer tongue weight is the target for WD bar strength. There is some wiggle room as the bars are strong beyond their need and will not themselves fail due to normal cycle use. So you can go one notch weaker for a more gentle tension profile. Going stronger risks trailer damage so you will want to do that purposefully.

Quote:
Currently using 1000 lb bars. These seem to be doing the job but they do get cranked up tightly.
And yes for this experiment the WD bars were tightened only enough to keep the stinger level.
The weaker bars will require more displacement to obtain the ideal tension but if you have more adjustment left then you are good. Only switch them out if you have a specific technical reason to do so.

The loads are all torque based and linear with respect to the moment axis so you can measure at one spot and calculate it at another. On the stinger as you did is problematic for calculations because the WD bars had some tension to hold the ball pitch fixed and that complicates the math a bit.
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Old 09-20-2020, 10:15 AM   #10
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I will have the trailer out again in a few weeks and will attempt the weigh again. Very busy with some fall projects at this time. For now I will let this sink in a bit.
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Steve, Christy, Anna and Phoebe (Border Collie)
1994 Classic 30'11" Excella - rear twin
2009 Dodge 2500, 6 Speed Auto, CTD, Quad Cab, Short Bed
Hensley Arrow hitch with adjustable stinger
WBCCI # 3072
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