tongue weight, dumb question - Fiberglass RV


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Old 07-14-2007, 07:56 AM   #1
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Realizing the importance of tongue weight to safe trailer towing, and getting ready to buy a travel trailer, I have a question. How do you measure/weigh it? I have always guessed, if my boat weighed 3000 lbs and I could hardly lift the tongue it was probably good enough --- not very scientific. Now I could be towing a trailer great distances with a load that can be adjusted and I should have at least 10% or more of the weight (4K-5K lbs) on the tongue. The typical bathroom scale won't cut it, are there special scales that you use or??? thanks, Ed
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Old 07-14-2007, 08:23 AM   #2
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One possibility:
A scale built into a hitch draw bar.
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Old 07-14-2007, 08:30 AM   #3
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This is how I calculated my tongue weight:
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(1) To weigh (my) trailer, I completely unhitched it, totally on the scale platform, with my tow vehicle off the platform, and the readout was [b]2620 pounds. Then I hitched up, but did not install the WDH spring arms. With the tow vehicle off the scale and the trailer on the scale, the readout was [b]2420 pounds. I deduced from that a hitch weight of [b]200 pounds.
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Old 07-14-2007, 04:27 PM   #4
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Here's a simple method for weighing your tongue with a bathroom scale.
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Old 07-14-2007, 06:19 PM   #5
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Don't forget the sherline tongue scale Sherline scale

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Old 07-15-2007, 08:44 AM   #6
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One possibility:
A scale built into a hitch draw bar.

The link in that thread is no good - did they go out of business?
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Old 07-15-2007, 12:28 PM   #7
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Don't know about out of business. Here is a link listing the item for sale JPCycles - SenZbar

I doubt it would retain it's accuracy for very long.

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Old 07-18-2007, 08:53 AM   #8
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Don't forget the sherline tongue scale Sherline scale

Curt
That Sherline product looks like a great tool. I have several trailers and knowing the real tongue weight would be nice (although I have been getting by for close to 40 years by guessing). Anyone have any input on accuracy and reliability of the sherline? It looks real rugged. Ed
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Old 07-18-2007, 09:33 AM   #9
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The Sherline scale is simply a hydraulic cylinder with a cross-sectional area of one square inch. That way, the pressure of the fluid inside in pounds per square inch equal the force pushing the piston down in pounds. You can use any hydraulic cylinder this way if you know the area (or work it out with a known weight), but sizing it this way makes it easy to use (no conversion factor needed).

There are four sources of inaccuracy that I can think of offhand:
  1. pressure gauge inaccuracy: depends on the gauge
  2. reading the gauge - can you eyeball the needle position well enough?
  3. cylinder off vertical - if the cylinder is off of vertical, it will read the force along the cylinder direction, not the weight (vertical force)
  4. stickiness - there will be a little bit of sticking in the seals, and it will be worse if there is (incorrectly) side load applied
I don't think any of these will be significant, and I expect that the scale probably works quite well, but that's just my feeling without quantitative evidence.

Since our tongue weights are so low, I think this scale would be best chosen lowest range gauge (0-1000 psi; that would make the markings easiest to read, and since the accuracy of a pressure instrument depends in part on the range it needs to cover, the instrument error would be lowest as well. Since most of us never need even half of that range, and even lower (e.g. 0-600 psi) range gauge would be even better.
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Old 07-18-2007, 11:06 AM   #10
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One nice thing about 13 footers is that we don't need special products or math formulas -- proper tongue weight will be less than 300 lbs. Just put your bathroom scale under the front of the tongue, with a chunk of 2x4 to bring the trailer to level. Voila - the scale should give a pretty accurate tongue weight.
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Old 07-18-2007, 03:51 PM   #11
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Rather than spend money on special scales, my personal preference is to spend the money on scales where I can weigh the tow vehicle and trailer, axle by axle, and do the math to get the tongue weight. Just knowing the TW, without knowing the trailer's actual loaded weight, isn't sufficient for my purposes...
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Old 07-18-2007, 07:54 PM   #12
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Quote:
The link in that thread is no good - did they go out of business?
Hmmm... It works for me.

http://senzbar.com/

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I doubt it would retain it's accuracy for very long.
Definitely not if you tried to TOW with it. It's not made for that.
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Old 07-19-2007, 10:53 AM   #13
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One nice thing about 13 footers is that we don't need special products or math formulas -- proper tongue weight will be less than 300 lbs. Just put your bathroom scale under the front of the tongue, with a chunk of 2x4 to bring the trailer to level. Voila - the scale should give a pretty accurate tongue weight.
That idea was recommended to me last week and it's a good one, except...I have a digital scale! I'll have to borrow/buy one with a needle to make it work.
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Old 07-19-2007, 12:29 PM   #14
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One nice thing about 13 footers is that we don't need special products or math formulas -- proper tongue weight will be less than 300 lbs.
This is what I do for my 17' Boler, as well... it is within the 350 lb capacity of my scale, although it would be slightly over the 300 lb capacity of some common bathroom scales.

Quote:
Rather than spend money on special scales, my personal preference is to spend the money on scales where I can weigh the tow vehicle and trailer, axle by axle, and do the math to get the tongue weight. Just knowing the TW, without knowing the trailer's actual loaded weight, isn't sufficient for my purposes...
Since our highway scales are free, the cost of total getting trailer weights is not an issue for me; however, as tongue weight sources they have two problems:
  1. they're not in my driveway, so they can't be used to determine weight distribution until the trailer is loaded and on the road
  2. they are not very sensitive, because they are intended for large trucks, so when the difference is taken between two weights to determine tongue weight, it's not very accurate
I agree that total actual loaded weight is important.

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That idea was recommended to me last week and it's a good one, except...I have a digital scale! I'll have to borrow/buy one with a needle to make it work.
I use a digital scale, and it works for me. There is a knack to getting it to lock on the tongue weight, but it can be done. Scales vary, and it is probably impractical with some digital scales; I have not seen an inexpensive electronic scale with manual zero/reset/hold controls.
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Old 07-19-2007, 09:37 PM   #15
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Hmmm... It works for me.

http://senzbar.com/

Hmmm... Yep, works for me now, too.

Must have been an internet burp.
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Old 07-24-2007, 03:57 PM   #16
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http://senzbar.com/
Definitely not if you tried to TOW with it. It's not made for that.
Not so, according to the manufacturer; it is made for towing. See my new post #8 in the previous topic [b]Unique Tongue Weight Scale.

If I had a 2" receiver box, I would be very tempted to buy one of these and use it to tow my Boler, which is about half the rated total trailer capacity, and one third of the tongue weight capacity, of the drawbar.
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Old 07-24-2007, 04:39 PM   #17
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Here's a simple method for weighing your tongue with a bathroom scale.
I wish this drawing would go away forever. As I have pointed out before, it is wrong when it says to "multiply the scale value by the distance between the pipes.

When I use this method, I set the 'pipes' four feet a part and the hitch jack at the exact center. If I did what they said my hitch would weigh about 864 lbs. Where in fact in fact the weight is 432 lbs. or 'the distance between the pipes divided by the distance between the hitch jack and the scales times the scale value'.

OBTW, you also have to transpose the weight from the hitch jack to the hitch ball.
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Old 07-24-2007, 05:08 PM   #18
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I use that method to get my hitch weight.I just reread the articale and it says to multiply by distance between pipes.I only multiply by distance from center of jack to pipe.Now you got me wondering.
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Old 07-24-2007, 05:53 PM   #19
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I wish this drawing would go away forever. As I have pointed out before, it is wrong when it says to "multiply the scale value by the distance between the pipes.

When I use this method, I set the 'pipes' four feet a part and the hitch jack at the exact center. If I did what they said my hitch would weigh about 864 lbs. Where in fact in fact the weight is 432 lbs. or 'the distance between the pipes divided by the distance between the hitch jack and the scales times the scale value'.
Charles, I agree that your value is correct for your setup, but the drawing's direction is also correct, if you follow all of their instructions. By insisting that the distance from the fulcrum pipe (the one shown on the right) to the tongue support point is exactly one foot, then the required factor of is simply the number of feet between the pipes... it is planned to be simple.

Also, 'the distance between the pipes divided by the distance between the hitch jack and the scales' would not be correct; it should be 'the distance between the pipes (the lever arm length for the scale) divided by the distance between the hitch jack and the fulcrum pipe (the lever arm length for the load)'.

I assume that the reading in this case (for Charles' trailer) is 216 lb (a 432 lb hitch weight, divided by two by placing it in the middle of a four-foot board, [b]two feet from the fulcrum). To completely follow the published method, the hitch weight would be placed at [b]one foot from the fulcrum, the scale reading would be 108 lb, and the "multiply the scale value by the distance between the pipes" method would correctly return 432 lbs.

Quote:
OBTW, you also have to transpose the weight from the hitch jack to the hitch ball.
If weighing at the jack, I agree a further correction is required; however, I assume that the illustration is intended to show a vertical strut (a piece of pipe, or lumber) from the board up into the coupler socket. It does look like a jack leg.
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Old 07-24-2007, 06:19 PM   #20
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I use that method to get my hitch weight.I just reread the articale and it says to multiply by distance between pipes.I only multiply by distance from center of jack to pipe.Now you got me wondering.
Sorry, Chester... your tongue weight is even higher than your thought.

This is a lever problem, and I think most people find levers easiest when the fulcrum (the pivot point) is in the middle (that's a first class lever), but in this case it is at one end (second class lever). Like any lever calculation, what is needed is a ratio of lengths from the fulcrum; in this case, those are
  • the distance from the load (jack, whatever) to the fulcrum (the pipe shown on the right) - this is what the procedure wants to be one foot
  • the distance from the scale (the pipe shown on the left) to the fulcrum (the infamous distance between the pipes)
As Charles noted, the scale reading must be multiplied by the ratio of those lengths, which is 2:1 in his case, and 3:1 or 4:1 in the illustrated example.

So, Chester, what are your lengths and scale reading... lets work them out. The good news: if you really are using the tongue jack, then compensating for that (again, as Charles mentioned) will lead to a slightly lower number.
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