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Old 05-21-2020, 08:58 PM   #1
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Effective vs Actual Tongue Weight 2

Hi Folks, The 2 in the title implies this is a second post since I am not sure the first worked. I’m new here. Will look at Bambi 16’ and 20’ tomorrow. The Bambi 20’ has stated tongue weight of 540lb. In the Bambi Owner’s Manual under weight distribution hitches Airstream states that when used properly the hitch transfers 1/3 of tongue weight to the trailer axle and 2/3 of tongue weight to the tow vehicle. Does this then imply that, in effect, the truck is only “feeling” 360lb of the tongue weight and that we use that number when we run the calculation for Gross Vehicle Weight?
Thanks, Stephen
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Old 05-21-2020, 09:17 PM   #2
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Yes, that is a fairly good guideline, if you use a WD hitch. However if you are that close to GVWR with the base tongue weights that you are worried about 180 lbs then you may need a tow vehicle with more capacity. The stated weights don't include any water in any of the tanks and no cargo. You should add 7 lbs for each gallon of water capacity and then 150-300 lbs for other stuff and figure 15-20% of all that is going to end up on the tongue then use the 1/3-2/3 guideline.

Tell me about your planned tow vehicle , perhaps I can help.
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Old 05-21-2020, 09:55 PM   #3
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BayouBiker,
Thanks. I did add weight of water at 28 gal times 8.34lb/gal, 200lb of food, pots, pans, dishes, misc, cloths and even 100lb for generator to be transported in the trailer, but I only used those lbs in determining the Gross Trailer Weight. I did not add percentage of the extra weight to the already 540lb tongue weight. So I see your point and will rerun my spreadsheet adding some percentage.

The tow truck is a 2018 Toyota Tacoma CrewCab 4x4 OR 3.5L V-6 with full Tow Package. Toyota specs say max gross trailer weight 6400lb and max tongue weight 640 lb. My gross trailer weight (3790+225 for fresh water+200lb for food and incidentals+100lb for generator) is 4315lb which is 67% of allowed max gross trailer weight of 6400lb. But I was concerned that the 540 lb tongue weight was pushing my gross vehicle weight rating a bit high (5447lb actual vs 5600lb max allowed). As such I though if the WD hitch actually relieves some of the actual tongue weight I would be less concerned. I will look at spreadsheet tomorrow, add 15-20% of extra trailer load to the tongue weight and then see where the 2/3rds puts the tongue weight at.
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Old 05-22-2020, 04:15 AM   #4
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Quote:
Originally Posted by smsasf View Post
Hi Folks, The 2 in the title implies this is a second post since I am not sure the first worked. I’m new here. Will look at Bambi 16’ and 20’ tomorrow. The Bambi 20’ has stated tongue weight of 540lb. In the Bambi Owner’s Manual under weight distribution hitches Airstream states that when used properly the hitch transfers 1/3 of tongue weight to the trailer axle and 2/3 of tongue weight to the tow vehicle. Does this then imply that, in effect, the truck is only “feeling” 360lb of the tongue weight and that we use that number when we run the calculation for Gross Vehicle Weight?
Thanks, Stephen
The truck will always support the full tongue weight of the trailer, there’s no way around that.
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Old 05-22-2020, 04:42 AM   #5
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Welcome Aboard 👍

The tow vehicle will 'feel' all the weight including the tongue.
Add at least 300lbs to the TW...that may be high but BSTS.
TW is measured most accurately on a scale with a with a level,fully loaded for camping rig.

Good Luck

Bob
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Old 05-22-2020, 06:16 AM   #6
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My suggestion is to just order a Sherline scale and take it to the dealer when you look at trailers if TW is an issue. I think that is the only way to know for sure what you are getting . Yes, the WD hitch transfers some of the weight back to the trailer but I doubt if it is 1/3. I have no idea how to "count" that weight.
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Old 05-22-2020, 06:39 AM   #7
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The workings of tongue force seems to confuse a lot of people. It is made more challenging by the confusion created by the word weight, which in English means both a force/load and mass.

Tongue weight is a load created by the torque of the trailer Center of Gravity (CG) around the supporting axles. The tow vehicle supports that load with a counteracting torque around the rear axle generated by shifting sufficient load from the front axle to balance the tongue load as Profxd indicated.

A stable system at rest must have all loads balanced by counter forces. Thus, as it sits 100% of the tongue is now supported by the rear axle of the tow vehicle along with the load shifted to the rear from the front plus the original unburdened load. The load on the trailer tires at this point is unchanged.

By adding Weight Distribution bars and adding tension to them a new torque generated load around the tow vehicle rear axle is added to the trailer at the point the bars connect to the trailer frame. Some of that load is distributed/supported by the trailer axles but most gets gets added to the tongue. To balance the force created by the WD bars acting around the tow vehicle rear axle, load is shifted from the rear axle back to the front axle.

The end result of WD is that it added load to the trailer axles and the tongue and shifted weight from the rear axle to the front axle to balance that load. the Trailer axle has/sees more net load with WD, the tow vehicle rear has less net load and the tow vehicle front has more net load. The tongue also more net load.

The receiver has less torque and stress with WD since the counter torques are acting through the receiver. WD stresses the receiver when backing ,when porpoising over bumps and when traversing uneven terrain. the uneven terrain is the worst as it causes a twisting stress on the receiver.

So Profxd is correct in a sense that the tow vehicle supports the full force of the tongue, it does, but WD adds another force that shifts load from the tow vehicle to the trailer. So the tow vehicle sees less total load and the trailer axles see more total load with WD.
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Old 05-22-2020, 06:55 AM   #8
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Originally Posted by Bill M. View Post
My suggestion is to just order a Sherline scale and take it to the dealer when you look at trailers if TW is an issue. I think that is the only way to know for sure what you are getting . Yes, the WD hitch transfers some of the weight back to the trailer but I doubt if it is 1/3. I have no idea how to "count" that weight.
Correct, this 3rd, 3rd, 3rd thing has always bothered me. If a theoretical rig had a distance from trailer axle to tv rear axle equal to tv wheelbase, then one would have close to equal distribution. In the real world, it is very different. The longer the trailer, the less is transferred to the trailer and more to the tv front axle for a given tv and rear axle weight removal.
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Old 05-22-2020, 08:57 AM   #9
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Originally Posted by Bill M. View Post
My suggestion is to just order a Sherline scale and take it to the dealer when you look at trailers if TW is an issue. I think that is the only way to know for sure what you are getting . Yes, the WD hitch transfers some of the weight back to the trailer but I doubt if it is 1/3. I have no idea how to "count" that weight.
It is fairly easy to estimate the ratio, actual results will be a little different because the suspension tie points are not centered on the axles and neither the tow vehicle or the trailer are rigid, rather they flex quite a bit. Notice though the length of the trailer has no influence on the distribution because the tension bars are fastened to the trailer and trailer torques cancel each other.

The ratio of weight transferred to the trailer axles (WTA) divided by the Tow Vehicle Front Axle (WTVF) equals the ratio of the length of the Tow Vehicle Wheel Base (LWB) divided by the sum of the length of the weight distribution bars (LWDB) plus the length of the ball to axle (LBA).

WTA/WTVF = LWB/(LWDB+LBA)

As Airstream indicated, this ratio will hover around 0.5 (1/3 divided by 2/3). For my setup it is 0.65 because my truck is long.

Edit: The Length of the trailer will influence how much tension is required to to shift the desired weight though. It will be inversely proportional. A trailer twice as long will require twice as much tension to shift the same load.
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Old 05-22-2020, 09:12 AM   #10
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Originally Posted by smsasf View Post
.......

The tow truck is a 2018 Toyota Tacoma CrewCab 4x4 OR 3.5L V-6 with full Tow Package. Toyota specs say max gross trailer weight 6400lb and max tongue weight 640 lb. My gross trailer weight (3790+225 for fresh water+200lb for food and incidentals+100lb for generator) is 4315lb which is 67% of allowed max gross trailer weight of 6400lb. But I was concerned that the 540 lb tongue weight was pushing my gross vehicle weight rating a bit high (5447lb actual vs 5600lb max allowed). As such I though if the WD hitch actually relieves some of the actual tongue weight I would be less concerned. I will look at spreadsheet tomorrow, add 15-20% of extra trailer load to the tongue weight and then see where the 2/3rds puts the tongue weight at.
Hi

Plus:

Passengers (check how Toyota figures them in, do they weigh 50 pounds? )

Weight of the hitch ( likely a couple hundred pounds)

Fuel for generator (if in the TV)

........

Best if you stay below 80% of the magic numbers. At 5600 lb max, a good spread sheet target would be 4,480 lb.

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Old 05-22-2020, 09:40 AM   #11
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I am getting a headache. The discussions of TW with a WD hitch has always confused me. Here is my take. Say you have 600 lbs of TW. Engaging a WD system will "transfer" this weight. It is not going to make this weight disappear nor will it increase this weight. Am I correct so far?


If some goes to the back of the trailer and some goes to the front of the TV, how can the weight at the hitch remain the same?....Now read this.



Quote:
Originally Posted by BayouBiker View Post
...


The end result of WD is that it added load to the trailer axles and the tongue and shifted weight from the rear axle to the front axle to balance that load. the Trailer axle has/sees more net load with WD, the tow vehicle rear has less net load and the tow vehicle front has more net load. The tongue also more net load.

....

I am interpreting load here as weight or the force caused by bearing that weight. Is this correct? If so, this statement means that the TW is actually getting increased. I am missing something here for sure.
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Old 05-22-2020, 09:44 AM   #12
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...

Edit: The Length of the trailer will influence how much tension is required to to shift the desired weight though. It will be inversely proportional. A trailer twice as long will require twice as much tension to shift the same load.

Isn't this "directly proportional"? If inversely, then twice as long would require half as much tension.
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Old 05-22-2020, 09:48 AM   #13
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Smsasf don’t go by the marketing specs. You can use the yellow door sticker which will show weights for ‘your’ truck. Even more accurate is to load up the truck as you would for camping and go to a truck stop CAT scale for actual weights. Also the published tongue weights of AS trailers always seem to be 100-200 lbs low. So the actual tongue weight will usually be higher. Also you need to add in the additional weight of the hitch system. Probably less than a 100# for a BlueOx or Equalizer.
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Old 05-22-2020, 09:51 AM   #14
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BayouBiker,
Thanks. I did add weight of water at 28 gal times 8.34lb/gal, 200lb of food, pots, pans, dishes, misc, cloths and even 100lb for generator to be transported in the trailer, but I only used those lbs in determining the Gross Trailer Weight. I did not add percentage of the extra weight to the already 540lb tongue weight. So I see your point and will rerun my spreadsheet adding some percentage.

The tow truck is a 2018 Toyota Tacoma CrewCab 4x4 OR 3.5L V-6 with full Tow Package. Toyota specs say max gross trailer weight 6400lb and max tongue weight 640 lb. My gross trailer weight (3790+225 for fresh water+200lb for food and incidentals+100lb for generator) is 4315lb which is 67% of allowed max gross trailer weight of 6400lb. But I was concerned that the 540 lb tongue weight was pushing my gross vehicle weight rating a bit high (5447lb actual vs 5600lb max allowed). As such I though if the WD hitch actually relieves some of the actual tongue weight I would be less concerned. I will look at spreadsheet tomorrow, add 15-20% of extra trailer load to the tongue weight and then see where the 2/3rds puts the tongue weight at.
As I mentioned before WD does relieve some of the load from the rear axle and does shift some of net load generated by the tongue to the trailer axles. It's a complicated situation that depends on the limiting factor used to set the payload limit. If you know it is suspension or axle related then you can safely make use of the load gained by shifting it to the trailer. If the limit is structural, generally the manufacturer addresses it by not increasing the tongue limit for WD. In your case I would presume it is a suspension/ride/comfort issue and would take advantage of the additional available load.
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Old 05-22-2020, 09:54 AM   #15
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Isn't this "directly proportional"? If inversely, then twice as long would require half as much tension.
Oops, yes aftermath, I misspoke, Appreciate the correction.
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Old 05-22-2020, 10:21 AM   #16
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I am getting a headache. The discussions of TW with a WD hitch has always confused me. Here is my take. Say you have 600 lbs of TW. Engaging a WD system will "transfer" this weight. It is not going to make this weight disappear nor will it increase this weight. Am I correct so far?
You can describe it this way and from a layman's perspective it's not wrong as this it one of net effects. Strictly though, Profxd is correct unfortunately, he didn't provide an explanation. The WD bars add a load on the trailer frame which shifts weight to the trailer axle. But the WD bars are affixed to the hitch receiver as an extension of the tow vehicle frame not the trailer tongue so transfer is not from the tongue, instead the transfer is from the tow vehicle rear axle. In fact, the WD bars add a significant additional load on the tongue. Part of the WD tension goes to the trailer axles but the bulk of it goes to the tongue.

Again you can think of it in the terms you used.


Quote:
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If some goes to the back of the trailer and some goes to the front of the TV, how can the weight at the hitch remain the same?....Now read this.
Remember, there is almost no mass at the ball and tongue. All (almost) the load there is torque generated. It is also unsupported and (largely) unrestrained. Therefore the torques at point where the ball meets the tongue must all cancel to zero in order for it to remain stationary. So the "net weight" always remains the same, namely zero. However the downward weight on the tongue is the original tongue weight plus the load generated by the tension from the WD bars. Therefore the upward force on the ball also increases by the same amount and it is generated by the other end of the WD bars fastened to the ball mount extended tot he frame so the lever moment for this force is the distance to the rear axle.

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I am interpreting load here as weight or the force caused by bearing that weight. Is this correct? If so, this statement means that the TW is actually getting increased. I am missing something here for sure.
No! You are spot on. I think you're picking this up!
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Old 05-22-2020, 11:07 AM   #17
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trade the taco for something with more beef. Reading you inquiry and all the replies sounds like you're dancing around disaster.
Good luck.
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Old 05-22-2020, 11:52 AM   #18
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The 1/3 - 1/3 - 1/3 load distribution with a WDH is a myth, as has been explored in other threads here. We had our truck-trailer weighed December 1, 2019 (fully loaded for travel) by the Escapees SmartWeigh service at their Sumter Oaks RV Park in Bushnell Florida. Individual wheel weights for all axles. Truck alone and then truck plus trailer with ProPride 3P WDH adjusted to make the trailer near level (slightly tongue low). The gross weight of the truck went up by 900 lbs. We calculated that the static tongue weight (with the PP 3P hitch) was 1,034 lbs., 134 lbs. or ~12.9% of which was transferred to the trailer axles. The other 87.1% was on the truck. IIRC, Sean at ProPride has reported that something like 10% - 80% - 10% is much more in line with reality than the 33% - 33% - 33% that is so often cited. Note that the spec'd tongue weight for our trailer is ~800 lbs. That is for an empty trailer, as built, and without the added weight of the WDH system. As someone else pointed out, the published tongue weight is not the actual tongue weight.
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Old 05-22-2020, 12:28 PM   #19
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The rule is often misquoted. Strictly, the rule is 1/3 rd of the weight transferred by the WD hitch goes to the trailer 2/3 rds returns to the front axle. Note though it is of the weight transferred not the tongue weight.

However, if you happen to have a fairly short wheel base vehicle like an SUV or a short bed no crew cab truck and you added enough tension to return 100% of the shifted front axle weight, the WD weight is similar to the tongue weight and the 1/3 of tongue to trailer 2/3 to rear tow vehicle axle 0 to the front would apply.

In order to achieve 1/3, 1/3, 1/3 you would need an extended crew cab or a crew cab long bed (a pro pride or Hensley would also help here) and you would have to add double the recommended WD tension, not a good idea.
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Old 05-22-2020, 01:55 PM   #20
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To me it seems that the published tongue weight is often close to the payload of the TV used after weight distribution is applied to transfer weight to trailer. Normally good enough to assume it's close until getting to a scale.
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