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Old 01-06-2012, 10:08 AM   #113
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Originally Posted by Airtandem View Post
we have been discussing the stiffness of the bars of the Equilizer hitch and the damage they can cause. after I got the 98, (not foot) home I noticed that the A frame had a slight upward bend and there were cracks in the skin at the corner of both battery boxes not to mention the leaks.
On the A frame were holes where SOB of hitch had been installed.I believe it might been of the bar chain type. If this is true, there should have been sufficient flex to have prevented the cracks and bend in the A frame.
Just some thoughts, and from my experience. Now back to the discussion.
mike
Not necessarily, You can also get very heavily rated "chain" type bars as well.
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Old 01-06-2012, 10:15 AM   #114
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OK, so have we (mostly, Andy's not with us, for sure) arrived at some level of concensus that "high frequency, low amplitude" shock loads from the TV are not significant contributors to AS damage? (I still think there may be room for discussion on, for example an empty 3500 dually and a small tongue weight AS vs. a 3500 loaded to cargo capacity....in other words COMPLIANCE of TV and AS suspensions at GIVEN CARGO LOADS.)

NOW, are we ready to move on to "low frequency, High Amplitude" inputs...ie. large angle changes between AS and TV frames. This is where my most concerns are with heavy bars....and where Andy and I are completely on the same page.
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Old 01-06-2012, 10:36 AM   #115
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Originally Posted by Inland RV Center, In View Post
The numbers, while it may answer some questions, doesn't really matter.

What does matter, is the stiffer the bars, the more shock is transfered to the trailer.

As an example, lets use railroad track for bars. Will they bend? Heck no. Then all of the forces from bumps etc, will be directly transfered to the trailer.

Now lets use broom sticks for bars. Skip the fact they we all know they will easily break. But, since they will easily flex, less forces will be directed to the trailer.


Andy
Andy,
Although it is dangerous to try to interpret what another is saying, I am going to take a stab at it. I think you are describing here a condition of one kind, and assigning it to another. I'd like to try to differentiate the two.

Condition 1
A TV with rock solid stiff suspension that has just about no give at all. The heaviest of heavy duty. When the back end goes over a little bump you get a CLUNK as the tires jump up and down to the pavement. The suspension has virtually "no compliance." No give when you jump up and down on the back. Ok? Let's call this "Hard TV."

Condition 2
A hitch using a stiff WD bar. Let's say the hitch weight is 500# and the WD bars is rated at 1200#. Here the WD bar is clearly a much higher rating than needed for the hitchweight. This bar has essentially no give, no bend when the trailer is attached. But the TV here is just a normal 1/2 T SUV or something with regular suspension. Let's call this "Rigid Bar."

What would I say about these conditions?
  1. They mean DIFFERENT things to the trailer.
  2. It is easy to see how condition 1 (Hard TV) could cause trailer damage. On a chuck hole, the TV rear end will clunk up and down like a hammer on an anvil. This will be true no matter what kind of WD bar is used. I think this is the case you are really saying causes damage to the trailer. I would agree 100% conceptually. I can visualize the effect very clearly.
  3. Condition 2 (Rigid Bar) only seems like it is the same as Hard TV. It actually is not the same, but it appears visually to be the same. This condition is not at all the same as Hard TV. The TV suspension is working fine here, and has plenty of compliance, the bar has no compliance and doesn't even come into play. This is what is being posited by my thought experiment and sketch. The bar only LOOKS like it is a compliant suspension piece, but it is not. It's a deception - the bar is only a lifting member and a resistance to hinging.
  4. Take a trip with your AS in Condition 1, then in Condition 2 using a properly balanced WD hitch. I predict the rider inside the AS (I know, I know, but we are just imagining here) will feel a VERY harsh ride in Condition 1, and the ride of Condition 2 will be much softer. In condition 1 when the TV hops over bumps and slams down, so will the A-frame. That's the stress I think you are getting at Andy. But that won't happen in Condition 2 because the TV in Condition 2 has lots of ....dare I say it....compliance! The bar doesn't matter.
I totally respect your 45 years of hands on experience, and I don't want you to think I am challenging your experience. I am not. I am only trying to clarify these questions with the words we all use. Words can create a confusion all their own, as we all know. Please...nobody take any offense here. I intend none.
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Old 01-06-2012, 10:38 AM   #116
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Originally Posted by dznf0g View Post

NOW, are we ready to move on to "low frequency, High Amplitude" inputs...ie. large angle changes between AS and TV frames. This is where my most concerns are with heavy bars....and where Andy and I are completely on the same page.
ha ha...I feel I am almost ready. But I would like to see if maybe Andy nods with my Condition 1, Condition 2 proposition.
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Old 01-06-2012, 11:55 AM   #117
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ha ha...I feel I am almost ready. But I would like to see if maybe Andy nods with my Condition 1, Condition 2 proposition.
I agree, partially.

But, again, non essential heavy duty bars add to the tow vehicles stiffness.

The less the trailer is forced to comply with a bounce, the more damage it will sustain.

That has gone on for my 45 years experience.

Heavy duty bars are OK, when needed, but they are not needed on a heavy duty tow vehicle suspension.

Andy
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Old 01-06-2012, 12:14 PM   #118
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ha ha...I feel I am almost ready. But I would like to see if maybe Andy nods with my Condition 1, Condition 2 proposition.
Nice clarification point. Only thing I would add to your excellent write up. I ASSUME in both 1 and 2 that the hop or bump is of a size and at a speed (elapsed time) which will cause no discernable change in angle for AS and TV frames, relative to one another. This is strictly a situation which we have loosly defined as "shock load"?
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Old 01-06-2012, 01:16 PM   #119
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Originally Posted by dznf0g View Post
Nice clarification point. Only thing I would add to your excellent write up. I ASSUME in both 1 and 2 that the hop or bump is of a size and at a speed (elapsed time) which will cause no discernable change in angle for AS and TV frames, relative to one another. This is strictly a situation which we have loosly defined as "shock load"?
Yes. That's exactly what I mean. Like chuck holes and tar strips and the like. Instantaneous bumps and shocks. This is the stuff that a coil spring in a car will absorb from the wheel and then release back into the wheel so that the car body doesn't feel it. When you imagine that coil spring working, that is the effect of compliance in the auto suspension. By comparison, the WD bars do no such thing. They do not allow for independent movement of the ball from the coupler, and therefore offer no compliance between those masses.
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Old 01-06-2012, 01:19 PM   #120
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gotcha, agreed.
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Old 01-06-2012, 02:04 PM   #121
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I've been trying to watch my trailer hitch while driving into and out of gas stations to see if anything looks well, too stiff. Casually, it looks like it works fine. But I really want my wife to video the hitch as I go over some dramatic gully or radical driveway entrance.

But even though I only casually observed it, this is my impression of what occurs. Since the speed of the rig is crucial to what happens, I will describe four scenarios.
  1. No bars or very soft bars and very slow speed. The coupler simply follows the ball down and then up as the car moves over the gully. The car suspension will compress only slightly if you go slow enough.
  2. No bars or very soft bars and a higher speed. The coupler simply follows the ball down and then up as the car moves over the gully. At some speed, you might compress the suspension enough to bang the hitch on the ground.
  3. Stiff bars and slow speed. This is where it gets interesting. As the rear of the TV body goes down into the gully the stiff bar wants to prevent the ball-coupler from flexing. It is holding the TV chassis and trailer chassis in a straight line. It holds the back end of the TV up from where it would normally go. This means the rear suspension of the TV must extend downward so that the wheel can contact the ground. The lack of "flex" in the ball-coupler is now compensated for by additional downward travel of the wheel. The coil spring is extending instead of the hinge bending. The movement needed to get over the gully has been transposed from the ball-coupler to the rear suspension. As that rear suspension extends down, the weight coming off the spring is moving directly onto the A-frame at the exact point where the rear of the WD bar attaches to the A-frame. If the gully is deep enough, and the bar stiff enough, the rear wheel might float above the ground. In that extreme case the A-frame will get the entire weight of the TV applied to that point attachment point on the A-frame. That looks like a real disaster. A 5600# weight could be applied right to the middle of the A-frame, in other words.
  4. Stiff bar, high speed. All the same forces apply as in #3, but now you might get some type of bounce if you go fast enough. Obviously this condition is a worst case version of #3. Since force is a function of mass times acceleration, higher speed will really multiply the force dramatically. Speed is a real enemy here.
The condition of 3 and 4 can be simplified to this: any time the rear wheel suspension is extending, weight is being transferred directly (and proportionally) to the point on the A-frame where the WD bar terminates mechanically. This will be happening when the TV goes over swales in the road, and surely when you traverse driveways. You can "simulate" this by simply putting the trailer jack on a stand, and then adding a several thousand pound weight about half way back on the A-frame. I bet there would be quite a deflection.



It seems to make a pretty good case for getting your bars fairly close to what is needed to lift the TV and not too much more. 1200# bars on a 500# hitch weight is probably a bad case, 1000# bars on a 800# hitch weight is probably not such a problem.


In any case, you could judge the problem visually by seeing how much your rear suspension extends down when you go over a driveway entry. If the wheel is only extending an inch or two from nominal that's one thing. But, if it is extending several inches, that is a direct picture of how much TV weight is being transfered to the A-frame at that moment.
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Old 01-06-2012, 02:27 PM   #122
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Making reference to # 3 and # 4, we must remember that the A-frame is bending, which transfers that energy to the shell.

Andy
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Old 01-06-2012, 02:33 PM   #123
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Agree with your analysis anecdotally....I believe your supposed numbers are off. I would also definitely warn against your final statement. Bar ratings do not necessarily reflect flexibility. When you go over that steep angle drive it is better, I believe, to look at bar deflection at a given angle deviation between AS and TV. Please refer to Andy's bar deflection graph. Note the flexibility is determined by the steepness of the graphed line. the steeper, the more flexible. Note the difference between the 1000# bars.

Go to Inlandrv.com under the articles tab, then select the torsion bar story

In my case, I had 1000# EQ bars and 900lb tongue weight. At a given driveway angle, there was not much additional deflection of the EQ bars and the front suspension compressed some and the rear suspension extended quite a lot....disturbingly so. With the 800# Reese bars and 900# tongue weight, I see about an additional 2" of spring deflection, minor front suspension compression and a little rear suspension extension. If you look at the difference in slope on Andy's graph between the EQ 1000# and the Reese 800#, you can see for a given deflection the difference in force required to accomplish the task.

These are only observations and estimations, of course and not accurate measurements, but I have observed them quite a bit.

I have come to the GENERAL belief that recommending the bar rating ONE rating BELOW your actual tongue weight for REESE is a great starting point in a proper setup.

With EQ, I BELIEVE that numerical gap should be greater. I am still looking for a set of 600# bars CHEAP to sleeve and install in my 10,000# head.

I think it prudent to state here, I THINK IT WOULD BE A VERY BAD IDEA AND UNSAFE TO USE A SHANK, RECEIVER, BALL, AND HEAD RATED BELOW THE TOTAL WEIGHT OF YOUR TRAILER.

Let the FUN begin!
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Old 01-06-2012, 03:02 PM   #124
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I think the worst case looks like this sketch. Mass must be shifted back to the A-frame any time the coil spring extends down. The amount of mass shifted is proportional to the amount of spring extension. The amount of force applied to the A-frame begins with the simple weight transfer, but becomes a bigger force as you speed up.
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Old 01-06-2012, 03:07 PM   #125
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Ok---it's going to take me a bit to thoroughly dissect your comments so I am sure I understand them. Thanks! Looks very interesting.
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Old 01-06-2012, 05:03 PM   #126
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Redwood,

I'm seeing, maybe, what you are saying and the drawing in post 123 helps a lot to visualize it.

I wonder if it makes a difference?—if this were such a problem, wouldn't there be lots of reports of bent tongues? With thousands of RV's, many with stiff hitch systems, driving over dips every day, I would think we'd hear about a problem. Some cheap trailers probably have weaker tongues than Airstreams and it would seem they would be having even more problems. I realize over time the tongue could be stressed so many times that eventually it would deform, and it would not be obvious what caused it, but even then, wouldn't there be reports of that? I also wonder if in the early days of trailering bent tongues were common before manufacturers leaned how to make them stronger.

Maybe it could be phrased this way—how much force has to be applied to the tongue to make it permanently deform? I assume it can bend temporarily and then return to normal. I have a vague memory of this being tensile strength. What can happen to the trailer in that place between no deformation and permanent deformation of the tongue?

And will something else (hitch parts, hitch receiver, coupler, etc.) give way before the tongue bends permanently? What is(are) the weak link(s)?

I'm sure there's a definite amount of force that can be applied driving through a dip that will bend a tongue or cause other trailer damage. Is that force so great damage is highly unlikely for almost any event? How does speed change the force? The answer in 4 in post 121 seems to be bounce makes it worse and although bounce certainly appears to bang the trailer a few more times, this is separate from the effect of stiff bars. I don't know what that means in reality.

The idea of the tow vehicle wheels leaving the ground (not from bounce) could have a couple of effects—slowing of the vehicle or a jerky result from wheels hitting ground and grabbing hold again. This reminds me of the pictures from years ago of the Toronado without rear wheels towing a trailer—could front drive and no rear wheels solve all problems? (Don't take this suggestion seriously?)

I hope I not going far afield and remember, there are no dumb questions (though perhaps dumb questioners). I am not saying "So what? This is all academic." I'm enjoying trying to understand this. The gas station example, or a steep driveway example, are good for illustration, but few people would hit them at anything but very slow speed. More a concern is an unseen giant pothole or the frost heaves in Alaska and northern Canada, and those are things I have driven through.

Rock on.

Gene
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