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Old 07-29-2019, 10:28 PM   #1
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Testing the 10% tongue weight rule

I was curious about that “10% rule”. You know the one that says whatever you load in your coach you can presume 10% of the weight will be added to the tongue weight. So, I though I’d test that out. After this exercise I'm not so sure about that rule.

Home made tongue weight scale:
I watched this video awhile back and decided to build this apparatus to measure “Trailer Tongue Weight” using a bathroom scale. It took about 20 minutes to build. I calibrated it by measuring several items of known weight (including my own body weight) and it worked perfectly; surprisingly accurate and very repeatable.
Here's a link to the video:


So, I verified the coach was level and the home made scale was level (it makes a difference if it’s not level) and measured the coach tongue weight at 1145 lbs. I then made a number of weight changes and measured the tongue weight at each step. Below are the steps I took and below that is an image of the coach with the approximate location of each step annotated. Below that is a side view of the coach relatively lined up with the above image to show the location of the axles. Below that, image 3, is my bathroom scale tongue weight setup.

In step #2 I used my own body weight and had my wife take a weight reading. In step #3 I added a 30 gallon trash can to the rear luggage rack and added 25 gallons of water to it.

The weight indicated following each numbered step below is the weight after the specific step was completed. example: step #2, 1250 lbs is the weight after the 229 lbs was added.


#1. 1145 lbs Starting Tongue Weight

#2. 1250 lbs Added 229 lbs at diagram position #2 (46% of that weight xfred to tongue)
Removed 229 lbs at #2 back to 1145 lbs tongue weight.

#3. 1020 lbs Added 200 lbs water on the rear luggage rack. (63% of the 200 lbs reduced tongue wt.)
Removed the 200 lbs water from the rear luggage rack; back to 1145 lbs.

#4. 1022 lbs Removed a bunch of tools (168 lbs?) from two front storage compartments.
(I didn’t actually weight them, however, see #8 below.
Assuming 168 lbs was removed, 73% of the 168 lbs reduced tongue wt.)
New tongue weight is 1022 lbs.

#5. 985 lbs – filled rear gray tank with 30 gal. water (240 lbs) (15% of 240 lbs reduced tongue wt.)
Dumped rear gray tank; back to 1022 lbs.

#6. 1055 lbs – filled front gray tank 30 gal. water (240 lbs) (15% of 240 lbs added to tongue wt.)
Dumped front gray tank; back to 1022 lbs.

(interruption to science experiment)

#7. 1045 lbs – Wife cleaned the toilet and dumped unknown amount of water in the black tank so the
new starting weight is 1045 lbs.

#8. 939 lbs – moved all the tools from step #4 to the rear luggage rack. Though the actual weight was
unknown I can assume a 63% reduction in tongue weight as in step 3, therefore the tools
must have weighed 168 lbs. That seems about right to me, it was several boxes of tools
and took 3-4 trips.

Thought it was an interesting exercise and decided to share the results.
Attached Images
File Type: jpg Tongue Weight.JPG (169.1 KB, 18 views)
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Old 07-30-2019, 05:17 AM   #2
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I have seen those videos on those scales, they seem accurate.

You’re calling it a coach, isn't a coach something you drive?

Looks more like a travel trailer
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Old 07-30-2019, 05:50 AM   #3
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Good write up. The 10% rule or your version is new to me. The one I know of is a ball hitch should have at least 10% and a 5th wheel at least 15% of the weight on the tongue. Its just a known that WHERE you add weight - in front of or in back of the axle- will add or reduce the tongue weight. That's why the water tank is usually in the rear of- over or slightly in front of the axles.

Your experiment will help others understand that where you load extra weight will affect the tongue weight and that will affect the amount of sway you will get. Although tongue weight is just one of several things that will affect sway.
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Old 07-30-2019, 06:01 AM   #4
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Quote:
Originally Posted by Sprink Fitter View Post
I have seen those videos on those scales, they seem accurate.

You’re calling it a coach, isn't a coach something you drive?

Looks more like a travel trailer
Coach - Camper - RV - Trailer - Travel Trailer All the same thing anymore.

You are correct - Coach used to refer to a "motor home" but times have changed so call it what you want just have fun in it and remember to make some memories along the way!

Happy camping!
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Old 07-30-2019, 07:19 AM   #5
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Before a recent 2500 mile trip I weighed mine. Tongue was 858 and trailer was 6204 loaded but without any fluids. That’s 13.8%. It towed no problem even though I added about 30 gallons of fresh water after I weighed it. I don’t play around with changing location of contents as I have it where everything is in its place.
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Old 07-30-2019, 08:18 AM   #6
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Clarity the photo with load xfr ranges

Thanks for the feedback. Shortly after purchase I contacted Crossroads and asked about the transfer of weight to the tongue. They told me to remember the 10% rule. However, nearly all the storage in the TT is in the front, either under the bed or in a large pass thru directly behind the propane bottles and in large clothes closets directly above pass thru. The weight really stacks up on the tongue with this design.
Happy RV-ing.

I've updated the photo to better clarify the message. I'll post it here since I can't figure out how to edit the original message. Not sure how to make the image larger, it uploads as a thumbnail.


.
Attached Images
File Type: jpg Tongue Weight 2.jpg (92.8 KB, 13 views)
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