Weight of a 21 - Page 3 - Escape Trailer Owners Community

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Old 11-14-2013, 12:10 PM   #21
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Chicken!
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Old 11-14-2013, 12:23 PM   #22
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I'm retired and stop thinking years ago.
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Old 11-14-2013, 12:28 PM   #23
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Does that not-thinking feel pretty good? I'm on the verge of retirement and looking forward to that frame of mind. I can drive myself crazy virtually all the time!
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Old 11-14-2013, 12:39 PM   #24
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Quote:
Originally Posted by TAfraser View Post
The Anderson was installed, but the chains were not tightened for the measurements I gave. I did run it over the scale twice with the chains set two different ways, but the weight measurements went a different way then what I expected.
Tighter chains means less load on the tug's rear axle and more on both the tug's front axle and the trailer axles; that's the point of a WD system. Is that what you were expecting, and is that what you saw?

This, of course, has nothing specifically to do with the weight of an Escape 21'...
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Old 11-14-2013, 12:51 PM   #25
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Sorry, I didn't read all the way to this post before posting my response above:
Quote:
Originally Posted by TAfraser View Post
Using the WDH, adjusted wrong, with the trailer only on the scale, the trailer weight went down by as much as 200 lbs to around 3160#. I thought that transferring weight off the tongue would put weight on the truck's front axle and the trailer's axles. The trucks front axle weight did go up by 40 lbs.
Your understanding of WD action is correct, and the front axle change is as expected. I agree that the trailer axle weight reading change does not make sense

Quote:
Originally Posted by TAfraser View Post
While the trailer was on the scale, I loosened the chains (just checking) while watching the scale weight, and the weight of the trailer went up. The truck weight, including tongue weight, also went down. So what I saw was both the trailer and truck individual weights going down, while the front axle weight went up. The only thing that remained constant was the total weight of truck and trailer. So where did that weight go to?
As you know, it has to go somewhere. Also, the average position of all the loads must stay in the same place - the weight of the mass of the truck and trailer is in the same place. There is no physical way to transfer load from one end of the combined rig to the other, only to move it between the middle (the tug's rear axle) and the ends (the tug's front axle and the trailer axles).

I suspect that the problem arises from (necessarily) making separate measurements at each axle (instead of simultaneously) and changing the height of the coupler on a tandem-axle trailer with non-equalized suspensions. Even slight (an inch or two) changes in coupler height cause significant shifts in the sharing of load between the axles, which changes the effective axle position, which changes how much load is carried on the hitch. If you are seeing only the trailer axle load, you might not be aware of the tug rear axle load change. You don't have separate scales under each trailer axle, so you can't see if the distribution between them is changing.

Here's a possibility: you crank up the tension on the chains, the coupler/hitch rises, the tongue gets so much more load (instead of the trailer axles) that the net change on the trailer is a decrease when you expect an increase. The balance works out because the effective trailer axle load is located further back. It's just a theory, but when you try this again I suggest observing coupler/tongue height carefully.

See why I think WD systems are interesting, but I avoid them? Also, why I'm not a big fan of tandems?
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Old 11-14-2013, 01:07 PM   #26
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Originally Posted by azjack View Post
The Jeep weighs 5300# with 2 pax, When it had the equipment inside the jeep it was about 5800#, we then transferred the traveling equipment (we are travelers, not campers) into the trailer, Jeep was then about 5300#.
Thanks Jack - I just wanted to make sure that I understood that correctly.

Quote:
Originally Posted by azjack View Post
The sherline reading seemed to vary with level and chocking.
It absolutely will change with level, and I suspect TAfraser (Tom?) is seeing the same effect.

With a single-axle, tongue weight is moderately reduced by an increase in tongue height (the centre of mass of the trailer pivots back closer to the axle). The same thing happens in a tandem, but is overwhelmed by the transfer of load from the leading (forward) trailer axle to the trailing (rearward) axle, because they don't share load equally. The net effect is that tandem trailer tongue weight increases noticeably with the tongue higher, and vice versa, as the effective distance from the rear axle set to the centre of mass (weight) changes. In the extreme you could lift the leading axle right off the ground, leaving you with a very rear-set axle and the tongue taking a substantially greater share of the weight of the trailer.

Look at the tandem cargo trailers on a U-Haul lot - they don't have tongue jacks and the skid on the tongue is barely in contact with the ground when lowered down. I dropped one off after a rental and after unhitching it rolled across the lot with the skid barely skimming the pavement! The effect is even more pronounced with two Torflex suspensions which are independent of each other (leaf spring axles are usually linked together with an equalizer which helps them share load).

Now chocking is different. I think if the presence of a chock changes the Sherline scale reading that the scale may be under side load, not just straight up and down. That would be bad for almost any scale, and I expect it would cause binding in a hydraulic cylinder like the Sherline scale.
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Old 11-14-2013, 01:19 PM   #27
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Quote:
Originally Posted by TAfraser View Post
The reason I question the Sherline's accuracy is the following: I put the trailer tongue weight on the scale and received an indication of 380#. I then placed about 200 more pounds on the tongue and it indicated 580#. I then removed the 200# and the scale only returned to about 500#. If I do it again, but only use 100#, the Sherline doesn't return at all.
This sounds like it is sticking. The hydraulic pressure in the scale must correspond exactly to the piston area (which will have very little variance) and the load on it plus or minus friction in the seal. That friction and pressure gauge error seem like the only two likely candidates for significant error, and friction seems a far more likely cause of repeatability errors.

Quote:
Originally Posted by TAfraser View Post
I also received two different measurements depending on weather or not I lowered the trailer tongue onto the scale (only by 2") or raised the scale to the tongue with my hydraulic floor jack. Both methods are recommended in the Sherline directions.
I can't see why the method would matter, but the height would - see my previous post. Does lowering the tongue onto the scale end up 2" or more lower than raising the scale to the tongue?

Two inches of tongue height doesn't sound like much, but can makes a significant difference. Try raising the scale up to the tongue, then without changing anything else, raise it a couple more times in 2" steps, and see the readings... then to be thorough (because I think you will be, Tom ) go through the same heights on the way down to average out offsets due to scale cylinder friction. You could even start with the tongue lower than normal (lower the tongue jack), to see the tongue weight on both sides of the normal towing height. I expect a significant effect of height on tongue weight.


I think the Sherline scale is a brilliantly simple and effective design, which is why I adopted the idea for my own home-built scale. It does have its limitations, and it difficult sometimes to distinguish problems with the measurement from actual changes in the situation being measured.


And we were all told towing a travel trailer was simple...
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Old 11-14-2013, 02:40 PM   #28
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Does that not-thinking feel pretty good? I'm on the verge of retirement and looking forward to that frame of mind. I can drive myself crazy virtually all the time!
Don't you mean "drive yourself virtually crazy" because the other way, "drive yourself crazy, virtually", is what happens here on the forums!!!

Retirement is good, you do one thing a day and it takes all day to do it!!
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Old 11-14-2013, 02:41 PM   #29
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I knew as soon as Brian got on he could answer the question, my right side brain was not working this morning. Have to adjust for the time zones.
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Old 11-14-2013, 02:50 PM   #30
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Don't you mean "drive yourself virtually crazy" because the other way, "drive yourself crazy, virtually", is what happens here on the forums!!!
Hmmm... but I think "virtually" was intended to apply to "all the time", not "crazy", or "drive". It's all about where the comma is located.

For those who find this amusing - it may take an especially warped mind but there are lots of us - I recommend the book Eats, Shoots & Leaves by Lynne Truss.
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