Tongue Weighing Question

[Morbo]

Can someone explain why the material that is used as a base for a tongue scale matters?

The reason I ask is, I weighed my trailer's tongue at the storage unit and it was 640 pounds (I used concrete blocks to support the tongue weight scale). Then on a camping trip, I wanted to check it again, this time it was lighter by 40 pounds (I used orange leveling blocks to support the scale this time).

It seemed odd to change so much since the trailer load was the same, so I wanted to doublecheck. So today I weighed it 3 times. Once with concrete blocks as support, then again with one concrete block and some orange levelers, then finally with all orange levelers. The heaviest weight was with the concrete blocks (675 lbs), then a lighter weight was reported for the combination of a concrete block and orange levelers (660 lbs), then the lightest weight was with the orange levelers alone used for a base (645).

Not that it matters, but the trailer is a 23' Globetrotter with a max weight of 6300 lbs. (we are loaded close to that when we camp). The scale is a brand-new Sherline and I used the scale post in the ball socket on the trailer as the point of contact.

Thanks for any enlightenment you can shed.

[CharlesinGA]

Did you have the trailer exactly level every time? Out of level can easily make a 40 lb difference. Were the water tank and waste tanks filled or empty the same?

Charles

[SSquared]

On my 25 footer, changing the tongue height by the thickness of one lego-type block changes the tongue weight by about 40 pounds.

[Genebuilder]

Originally Posted by SSquared

On my 25 footer, changing the tongue height by the thickness of one lego-type block changes the tongue weight by about 40 pounds.

I don’t think the combination of two cinder blocks, then a cinder block and legos, and finally all legos would add up to the same exact height for all three stackups. First thing I would have measured to ensure no variability. Most likely cause of weight variation.

Why would the OP think the weight would change by changing stackups? The law of gravity doesn’t change with differing stackups as long as the trailer stays level…or the stackups are all exactly the same height.

[richard5933]

What's the accuracy/reliability of the scale? Could it just be that the scale has a consistency issue itself and will give you different numbers each time, even if you use the same base?

If the scale is accurate and reliable, then I'd suggest it's a height-related issue.

[Andy543]

You probably have air bubbles inside your hydraulic scale. This will give erratic readings. The Sherline manual has instructions for bleeding the air out.

[nelsonh]

I just acquired the 1000 lb Sherline scale and plan to weigh my rig with it tomorrow. FWIW the manual states that the scale's accuracy is plus/minus 2%. The manual also suggests using the scale on top of a hydraulic automotive (rolling type) floor jack, which I was planning to do because my driveway is not level, and using the jack will make it much easier to get the trailer level. And now that I've read this thread, it will allow me to observe the weight readings as I intentionally put the tongue higher and lower than level, just to see the effects that an out-of-level tongue have on the weight reading. Will post back with my findings since I'm certain everyone here is on the edge of their seats.....

[Morbo]

After reading the replies above, I suspect that the difference in height for each stack I used probably was the source of the variance. I didn't measure the height with a ruler, I just relied upon a bubble level on the tongue; probably not precise enough.

Now I have to go measure the height of each stack I used to see how much of a difference it made.

Thanks for the replies.

[Profxd]

It common for dual axle trailers to have a varying TW over a span of heights. It’s referred to as hysteresis.

[gypsydad]

I don't use the portable scale; I use CAT scales. Works for me. Tongue weight is just one part of the concern. Are CAT scales accurate? Are portable scales accurate? Make sure your level...get yourself a Level Mate Pro. (Also helps when parking.)

[nelsonh]

I weighed my (loaded for outing) trailer with the Sherline scale and it's right at 600 lbs in a level position. I had the scale on a hydraulic floor jack... I slowly raised the jack to get the rig out of level and was surprised to see that when I went all the way up to 3" higher than level, the weight was up to 700. I slowly lowered the jack and observed the scale, and essentially saw that the weight went back down by about 35 lbs for every inch of downward travel. I cannot offer an explanation into the physics of this phenomenon , I just saw what I saw. So my takeaway is that when getting a trailer tongue weight with a scale in this manner, you really want to be as level as possible to get the most "accurate" reading.

[Wazbro]

Originally Posted by nelsonh

I weighed my (loaded for outing) trailer with the Sherline scale and it's right at 600 lbs in a level position. I had the scale on a hydraulic floor jack... I slowly raised the jack to get the rig out of level and was surprised to see that when I went all the way up to 3" higher than level, the weight was up to 700. I slowly lowered the jack and observed the scale, and essentially saw that the weight went back down by about 35 lbs for every inch of downward travel. I cannot offer an explanation into the physics of this phenomenon , I just saw what I saw. So my takeaway is that when getting a trailer tongue weight with a scale in this manner, you really want to be as level as possible to get the most "accurate" reading.

With tandem axles with independent suspension like Airstreams have as you raise the front end it shifts the pivot point from between the axles further back toward the back axle until the front wheels come off the ground then it is at the back axle (if the back of the trailer hasn't hit the ground).

[Morbo]

Originally Posted by gypsydad

I don't use the portable scale; I use CAT scales. Works for me. Tongue weight is just one part of the concern. Are CAT scales accurate? Are portable scales accurate? Make sure your level...get yourself a Level Mate Pro. (Also helps when parking.)

That LevelMate Pro system looks pretty cool. Now I need another new tool for the trailer.

[nelsonh]

Originally Posted by Morbo

That LevelMate Pro system looks pretty cool. Now I need another new tool for the trailer.

It’s extremely handy and a very worthwhile upgrade IMO, especially when you’re leveling the rig alone. I highly recommend it. I saw that they are going to be releasing a new model/version soon ( or maybe already have) so there will be 3 models instead of 2, I’m not sure what the new features are/will be but I’d check their site.

[Profxd]

Originally Posted by nelsonh

I weighed my (loaded for outing) trailer with the Sherline scale and it's right at 600 lbs in a level position. I had the scale on a hydraulic floor jack... I slowly raised the jack to get the rig out of level and was surprised to see that when I went all the way up to 3" higher than level, the weight was up to 700. I slowly lowered the jack and observed the scale, and essentially saw that the weight went back down by about 35 lbs for every inch of downward travel. I cannot offer an explanation into the physics of this phenomenon , I just saw what I saw. So my takeaway is that when getting a trailer tongue weight with a scale in this manner, you really want to be as level as possible to get the most "accurate" reading.

All multi axle trailers will exhibit this to some degree. The SAE describes this in determining TW in their standard.

“ If a multi-axle trailer is used, it will be necessary to account for hysteresis in coupling load that results with coupling
height change. Coupling height and load shall be measured for at least one cycle of height change. Hysteresis will likely
increase with the magnitude of the cycle up to some magnitude of height change. The magnitude of the cycle shall,
therefore, be at least this large with the mid-point of the cycle being the coupling height at which the handling tests are
conducted. The coupling load is determined as the average of the maximum and minimum coupling loads at this
coupling height that are defined by the hysteresis loop.”

[gypsydad]

Originally Posted by nelsonh

It’s extremely handy and a very worthwhile upgrade IMO, especially when you’re leveling the rig alone. I highly recommend it. I saw that they are going to be releasing a new model/version soon ( or maybe already have) so there will be 3 models instead of 2, I’m not sure what the new features are/will be but I’d check their site.

I found the Levelmate to be a great investment, for sure! Saves the wife and I "arguing" about how "level" we are... side to side and front to back!

[Andy543]

What is a level trailer? Depends on where you're measuring it. For us, the most important thing to have level is the kitchen counter. You don't want to have water dripping off the end or peas rolling away. I always put a carpenter's level crosswise on the counter to check the level and adjust accordingly.

[richard5933]

Originally Posted by Andy543

What is a level trailer? Depends on where you're measuring it. For us, the most important thing to have level is the kitchen counter. You don't want to have water dripping off the end or peas rolling away. I always put a carpenter's level crosswise on the counter to check the level and adjust accordingly.

I think for the purposes of towing, it doesn't matter if the trailer is level or not - it matters that the trailer is in the same orientation as it is when being towed. I measure the height of the coupler when hitched, and then I put the scale on blocking to have it be the same height as it is when hitched.

My goal is to know the tongue weight that's being carried by the tow vehicle.

[Wazbro]

Originally Posted by richard5933

I think for the purposes of towing, it doesn't matter if the trailer is level or not - it matters that the trailer is in the same orientation as it is when being towed. I measure the height of the coupler when hitched, and then I put the scale on blocking to have it be the same height as it is when hitched.

My goal is to know the tongue weight that's being carried by the tow vehicle.

I believe you are correct for the purposes of this thread and determining tongue weight. With some setups you can't adjust to perfectly level so checking tongue weight with the same "level" as when set up for towing would be best practice.

[jadatis]

Originally Posted by Morbo

After reading the replies above, I suspect that the difference in height for each stack I used probably was the source of the variance. I didn't measure the height with a ruler, I just relied upon a bubble level on the tongue; probably not precise enough.

Now I have to go measure the height of each stack I used to see how much of a difference it made.

Thanks for the replies.

For single-axle TT or 5thwh the higher the tonge while measuring, the lower the weight gets, lower more weight.

For tandemaxle the other way around, higher on scale gives more weight, and lower on scale gives less weight.

For european TT , where mostly only 4% of total on tonge, if you let tonge of tandemaxle trailer hang free , it stops above the ground, because then zero weight on tonge.

The hight of the total grafity point also plays a role, the higher , more weightdifference at same hightdifference.


On Dutch tt forum I once made a topic about it, for single axle, wich most here are, from wich picture made with paint here. Yust to make you understand the basic idea.

For a single axlleTT with 10% on tongue the total grfity point is 10% of distance axle to tonge, so even has larger effect on weightdifferences.
For tandemaxle its more difficult, because of dynamic balance .