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.