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Old 07-15-2015, 09:02 PM   #1
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Tongue weight?

I have always thought that tongue weight is your friend when trying to set up a stable towing trailer. I have always been careful to load utility trailers and boat trailers s o they have a good percentage of tongue weight. Yet almost every day I read a post in which people are trying to reduce the tongue weight of their trailer by shifting the load or by other means. How does this reduction help make a stable tow. One person was going to move stored goods from the Airstream designed storage at the front of the trailer to over the wheels. I would prefer it to be in the front. Or am I just like the captain of the Titanic in that what I know for sure is wrong?
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Old 07-15-2015, 09:44 PM   #2
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Not enough information. It is possible to have either too much or too little tongue weight. Multiple sources say the Goldilocks range is 10-15% of TT GVW.

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Old 07-15-2015, 11:07 PM   #3
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Here's what my Airstream Owner's Manual says about it in the Towing section:

"WARNING: The tongue weight should he approximately 10% of the trailer’s total weight, but MUST NOT EXCEED 1,000 lbs. And, under no condition should it exceed the hitch rating. Your hitch installer should provide your hitch rating information."

I believe most of the Owners Manuals for late models have the same statement. Note that that our 2012 FC 25 maximum load is 7300 lbs, 10% for tongue weight is 730 lbs. The maximum load on any current production Airstream is 10,000 lbs, 10% is 1,000 lbs which matches their warning.

I also have loaded trailers (utility) heavy on the front to ensure stability after a particularly wobbly experience bringing home a load of lumber some years ago with a short utility trailer. So what you are saying makes sense to me, but for the Airstream I'll stick with their guideline and warnings.

My goal is 730 - 1000 lbs for our 25' FC, and I move loads around trying to ensure we stay within those parameters. Benefits are less tension needed on the w.d. bars, smoother ride, and more effective payload available with our truck. Without loss of stability demonstrated to us during many cross-country trips in all weather and traffic conditions, including dodging deer and quick-lane-change artists on the interstate.
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Old 07-17-2015, 10:26 PM   #4
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How does one measure tongue weight?
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Old 07-17-2015, 10:50 PM   #5
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google Cat Scale. Look at the how to drawings.

Search this forum for how to calculate different weights. You also should know the loads on tires, axles, hitch load (not the same as tongue weight), gross trailer weight, tow vehicle payload capacity, tow vehicle gross weight, load transferred by weight distribution, etc. Each component of the rig has its own load limits.

First weigh with the tow vehicle with trailer connected, with load distribution tensioned.
Second weigh with the tow vehicle with trailer connected, with load distribution loose.
Third weigh tow vehicle only.

This will give you information needed to calculate.

Cost $10 for the first weigh, then $2 for each additional during the same day.
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Old 07-18-2015, 06:08 AM   #6
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Question Question?

Has anyone confirmed that what AS recommends in the OM is 'tongue weight', (unhitched) or receiver load with WD set.

...I have never been below 900-1000lbs TW, but carry 800-840lbs with WD set.

Is AS worried about the TV receiver or the Airstream tongue construction/limit?...or both. Obvious you need to stay within the limits of the receiver, but are they saying the AS's tongue can't support more than 1000lbs?


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Old 07-18-2015, 06:17 AM   #7
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We have a heavy tongue at near 15%. We try to load a lot of our stuff over the rear axles. Works good for us. The 23' handles and tows fine with our car.
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Old 07-18-2015, 06:35 AM   #8
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What did your tw weigh in as?
I know this model (73 23') is nose heavy, but I've never actually weighed mine.
The nose-heavy tendency is why I'm not too concerned about adding 2 grey tanks and a bigger black tank in my renovation. Its not that much static weight added to the structure (tanks themselves, and the hardware to attach them), and I'll also probably never drive around with full tanks, either.
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Old 07-18-2015, 07:06 AM   #9
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He there Chuck.... I believe our era of 23' has a listed tongue weight of 590lbs and road ready we are at about 4,500lb on the axles. For our car we don't want it to go much heavier. Keeping our bikes and other heavier items loaded on the rear axle area seems to work well.
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Old 07-18-2015, 08:19 AM   #10
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Quote:
Originally Posted by LyleRussell View Post
How does one measure tongue weight?
This is what I use:

Sherline Trailer Tongue Weight Scale - 2,000-lb Capacity Sherline Tools 5780
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Old 09-11-2015, 08:34 PM   #11
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Quote:
Originally Posted by Bill M. View Post
I have always thought that tongue weight is your friend when trying to set up a stable towing trailer. I have always been careful to load utility trailers and boat trailers s o they have a good percentage of tongue weight. Yet almost every day I read a post in which people are trying to reduce the tongue weight of their trailer by shifting the load or by other means. How does this reduction help make a stable tow. One person was going to move stored goods from the Airstream designed storage at the front of the trailer to over the wheels. I would prefer it to be in the front. Or am I just like the captain of the Titanic in that what I know for sure is wrong?

I find the attached article useful for describing the effect of where the weight is in a trailer and hopefully it will answer your question.
Some of the other information might be troublesome for some, but that is not my intention.
The link was previously in a deleted thread that had a horrible title and possibly caused some upset.
Again, just hoping more information about our trailers won't hurt.
http://oppositelock.kinja.com/tow-me...qnbJxnyozIeA.2
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Old 09-11-2015, 09:54 PM   #12
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The location of the center of gravity, relative to the location of the axle(s), is a primary factor in establishing the yaw stability of a TV/TT combination.

"Tongue weight percentage" simply is a shortcut to expressing the ratio of distance from TT axle(s) to center of gravity divided by the distance from axle(s) to the ball coupler. Instead of saying the distance from axle(s) to CG is 30" and the distance from axle(s) to coupler is 200", we say the tongue weight percentage is 15%. Unfortunately, we then tend to focus on how much vertical load is applied to the ball rather than on how the TT exerts lateral forces on the ball.

A fundamental objective in designing a trailer is to minimize the lateral force which can be exerted on the TV by the TT when the TT is subjected to lateral force due to wind loading, lateral road force on tires, etc. The force imposed on the TV is a function of:
a = distance from axle to CG
b= distance from CG to coupler
M = mass of the trailer
I = polar moment of inertia of the trailer.

Without providing the derivation, the relationship among these four variables is given by:
a*b = I/M
From this equation, if you knew the values for M and I, you could calculate an "optimum" value for a/(a+b) which is numerically equal to TW%.

Unfortunately, a TT's polar moment of inertia hardly ever is known, so the equation is not of much use. However, we can use a special case to demonstrate where the "rule of thumb" values for TW% might come from.

Let's assume the mass of the TT is uniformly distributed front to rear. Then, given that a typical TT is relatively narrow compared to its body length (L), we can approximate its polar moment of inertia as:
I = M*L*L/12

If we put this special value of I into the equation for a*b and assume the TT has an A-frame length of 4' and L = 20',
a little algebra would give a = 14', b = 2.38' and TW% = 2.38/(14+2.38) = 14.5%.

However, we know that most real trailers do not have their mass uniformly distributed front to rear. Instead, they tend to have more of the mass located closer to the center near the CG and axles. This reduces the polar moment of inertia. If the value of I for the above example were reduced by 30%, the corresponding "optimum" TW% would be reduced to 10.6%.

Since each element of mass in the trailer contributes to the polar moment of inertia in proportion to the square of its distance from the CG, it's not hard to see that concentrating the mass near the longitudinal center can significantly reduce the inertia value. If you compare the layout of a typical European caravan with a typical US trailer, it should be easy to see why the Europeans can get by with a TW% as low as 7% in most cases and as low as 4% in some.

Unless you have some way of estimating the polar moment of inertia for your trailer, there is no good way of knowing the "optimum" TW%. Some people resort to seat-of-the-pants experimentation with varying TW to try to achieve "optimum" yaw stability.

Ron
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Old 09-11-2015, 10:38 PM   #13
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Quote:
Originally Posted by Ron Gratz View Post
If we put this special value of I into the equation for a*b and assume the TT has an A-frame length of 4' and L = 20',
a little algebra would give a = 14', b = 2.38' and TW% = 2.38/(14+2.38) = 14.5%. Ron
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Old 09-11-2015, 10:56 PM   #14
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I have to agree with what Ron says, but I had to learn it all by trial and errors. What I learned was to not put a "wad" of weight ( like a 26 gallon water tank) clear at the back of the trailer behind the axles even with 15% tongue weight. I did get sway! I learned it was not all just tongue weight. Mass distribution plays a large part of smooth towing.

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