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Old 03-28-2006, 12:36 PM   #61
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"""because the upward force exceeds the tounge weight. a force equal and opposite to the tounge weight would only level the load; not re-distribute it. i.e. airbags on a tow vehicle's rear axle...""

hi chuck and others.....

it's good to see the exchange about how w/d systems work.....and with enough examples, forumula, and trials we might have a good thread on w/d dynamics.....for all to learn from.

maybe we could move this info/exchange out of the bambi/sway control thread....

it would be nice to use nicks thread on 'calculations' or a new thread on w/d analysis, theory, and application....or some such name.

so folks can learn/understand regarding w/d's without debating the need for sway control on all size trailers......the point of the original post...even bambi needs sway control....

trulyvintage.....other states do have w/d requirements, like iowa....and those tow ratings you mention also usually require w/d systems for tongue loads greater than 500lbs...

it's correct only the driver may know what happened....and even he/she may not....really know.....and by the way this trailer pictured should be long rebuilt by now and resold....that was the plan.

but the bambi pictured did not have sway control attached. and the 'bacon' you mention being saved was likely the result of a suburban sized t.v. not being controlled by a small trailer flopping about...

chuck....
your analogy to rear airbags doesn't apply here, and it isn't how w/d systems work.....because there is not ground contact/support....under the connection.....like with an air bag setup.

the lifting noted at the hitch/ball assembly is a byproduct of how the w/d system applies force....to look at it as 'lifting' at the ball is misleading...in fact if the ground were soft enough under the front t.v tires and trailer tires....the w/d forces could 'level things' and redistribute without raising at the middle...but buy pushing down the front and rear support points..

cheers
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Old 03-28-2006, 12:39 PM   #62
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the resultant force at that spot is UP, otherwise, it wouldn't go UP.
It doesn't "go" up rather it 'stays' up. There is no net force or there would be movement. (Newton #2).

As with any beam, the load is transferred out to its ends (the axles in this case).

The force UP on the ball by the hitch is equal to the force DOWN by the ball (Newton #3) and is the resistance of the hitch to being deformed.

see Newton's laws of motion and Bending in wikipedia

For another model to consider: Think of a steel I beam that runs from the middle of your tow vehicle back to the trailer axle. The trailer ball sits on that. You couldn't steer very well but you'd certainly have very good load leveling.

Come to think of it, that model is pretty close to a Pull-Rite hitch.

Also, you should understand that these concepts are not an easy to understand. It sounds simple and it is simple but they are some of the more difficult conceptual ideas to teach in basic physics. It took centuries before Newton really laid them out and, in the centuries since, many in the general public still don't get it because it takes a bit of counter-intuitive thinking and work to figure it out.
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Old 03-28-2006, 12:55 PM   #63
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...other states do have w/d requirements, like iowa....and those tow ratings you mention also usually require w/d systems for tongue loads greater than 500lbs...
...
but the bambi pictured did not have sway control attached.
...
your analogy to rear airbags doesn't apply here
2Air, I haven't seen many states requiring weight distribution like I do for brakes. A lot of trucks don't need it and some even don't need it for mobile home transit.

I know that towing a Bambi with even a sedan doesn't necessarily need sway control and even a modest burb or IH Travelall might not need load leveling with it.

The rear airbags may well apply here as the intelligent suspension on some newer vehicles are designed to handle several hundred pounds of hitch weight without any load leveling requirements. It all depends upon the design of the tow vehicle.
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Old 03-28-2006, 01:05 PM   #64
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Originally Posted by Leipper
The rear airbags may well apply here as the intelligent suspension on some newer vehicles are designed to handle several hundred pounds of hitch weight without any load leveling requirements. It all depends upon the design of the tow vehicle.
i'm not suggesting airsuspensions don't improve load carrying and handling....on some newer vehicles...like the touareg, cayenne, rover and so on....or even on semis and mohos.

my point is lifting the t.v. at the rear axle (with air or springs or a jack) doesn't mimic how w/d systems apply stress/force via the frame to redistribute...

so i stand by the observation that 'air bags at the rear axle don't apply' to how spring bar/wd systems function.

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Old 04-02-2006, 08:01 PM   #65
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The test part 1

Earlier in this thread we had a discussion about the possibility of the trailer coupler jumping off of the ball if the coupler was released with the WD arm attached. The theory was that the WD arms are listing the rear of the TV by lifting on the coupler. Several laws of physics are involved here. Because of my teenage years in the sixties I sometimes ignore the laws that I don’t like or understand. I said I would test this theory and I did.
The first thing I did was to adjust the hitch ball in accordance with the instructions I downloaded from this site. The result was that my ball is now angled back to the TT several degrees, it was straight up and down before this. This adjustment most likely had nothing to do with the results of the test, but it needed to be done.
I used my 1075 Trade Wind with a listed tongue weight of 630 pounds. I attached my Reese WD hitch with 750 pound arms to the rear of my 2004 Tundra. (continued)
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Old 04-02-2006, 08:02 PM   #66
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The test part 2

The first test was t attach the trailer and leave the coupler unlocked. I then tried to lift the trailer off of the ball. 630 pounds, not a chance. (continued)
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Old 04-02-2006, 08:03 PM   #67
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The test part last

The next step was a little harder to do. I could not lift the trailer and TV with the trailer’s jack to help attach the arm. This made it quite difficult. I did place blocks of wood under the tongue of the trailer (just in case) but they did not touch. I did use my 6 ton hydraulic jack to raise the rear of the TV (at the hitch) and the trailer to attach the bars. The jack was removed for the lifting part of the test. I started with a small amount of tension on the arms and continued until I had gone one link past the level point for my TV. At that setting the rear of the TV was noticeable higher then the front and I had gone too far.

The result: At no point was the weight on the ball small enough to budge the coupler off of the ball. I even tried to leverage it with a pry bay and it would not move. The theory that the front of the trailer would be lighter is incorrect. I was wrong and I proved it. Thank you to everyone for not beating me up too much on this issue. Now can anyone explain why chuck said that his coupler rose into the air when he uncoupled the ball, I can’t.
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Old 04-02-2006, 08:22 PM   #68
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good post azflycaster

i just love show and tell!

as i understand, the forces around the ball should have actually increased, not decreased as the spring bars were progressively engaged....only a sensor between ball/cup could show this, but the complicated vector graphs and forumla i've seen indicate this...

seems we will need chuck to repeat his process.

again good job; thanks for sharing...

2air'
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Old 04-03-2006, 09:37 AM   #69
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Hmmm...I think we're all saying the same thing, but it sounds like we're saying something different. The concepts are difficult to describe with words.

2-air: on the airbags, that's what I meant. airbags are like a pillar; wd is like a beam. You can "level" the load with airbags, but not "redistribute" the load the same way.

Leipper: yes, "beam". I get that. a beam works by balancing tension and compression, right? its like a beam when its all hooked up and adjusted correctly. But its not really "a" beam; its 2 beams, overlapped, and strapped together ("sistered") at 2 points. the forces on those 2 connection points have to be balanced, too, yes? remove one without removing the other, and you've got a hinge.

the experiment: I'll have to try and mimic the same thing. It looks like very similar equipment...comparable trailer and tow vehicle (1/2 ton)...reese hitch, although, I don't know how strong the bars are (old, and not clearly labelled), and there is a dual-cam attached. but I don't think that should make a difference. perhaps I've just got it too tight. It was difficult to get what appears to me to be "acceptable" deflection with the wd system, according to the standard bits of advice. "tv should settle the same amount at both axles"..."vehicle should be level", (that is contrary to the first bit, because the vehicle wasn't level to begin with). You can't follow the Reese instructions to the letter, because the bars will touch the ground before they reach the recommended distances "x, y, z"...possibly just because of our lower-slung than usual trailers. (If the whole thing was 6" higher, you could do it...at least more easily.)

anyway, I'm thinking that one explanation is that my front axles are stiffer (in effect) than the rears...moreso than typical. And as a result of my trying to level the load by conventional advice, rather than using a scale as my only reference, has caused me to adjust my bars too tight. I can tell you that jumping up and down on the rear bumper of this truck, its like a spring-board. like a swiming pool diving board. jump on the front bumper, and it barely moves. I've seen discussions on my snow-plowing forum about why chrysler says you shouldn't plow with this truck (1/2-ton quad-cab; 1/2 ton regular cab is "approved"). The stretched cab and lack of a "b-pillar" puts proportionally more weight on the front axle than a "conventional" setup, and the added weight of a typical snow plow would exceed the axle rating. So there's so little slop in the front end, the results of adjustment to a wd hitch are deceptive. just a guess. I'll have to try and repeat the experiment in a couple of weeks, when we get hooked up.
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Old 04-03-2006, 10:42 AM   #70
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Chuck... please do. I think many of us were puzzled by your coupler "springing up". I've never observed that occur, and I've prematurely unlocked the coupler on mine a number of times on various tow vehicle/trailer combinations without experiencing what you described. It's always been my experience that without raising the tongue and tow vehicle with the jack, it's not coming unhitched... period.

Let us know what you figure out.

Thanks!

Roger
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Old 04-03-2006, 01:37 PM   #71
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airbags are like a pillar; wd is like a beam. You can "level" the load with airbags, but not "redistribute" the load the same way.
...
But its not really "a" beam; its 2 beams, overlapped, and strapped together ("sistered") at 2 points.
...
I'm thinking that one explanation is that my front axles are stiffer (in effect) than the rears...
Active suspensions are a bit more than just airbags. But even airbags can create load shifting to some degree by changing the attitude of the vehicle.

The beam idea should not be stretched to absurdity like getting into why a truss and a beam are different when the idea is to use a simple example that is common to both to illustrate a concept.

Your note on the heavy (and stiff) front end is typical of a lot of pickup trucks, especially diesels, and one reason why they often don't need weight distributing hitches, especially if they have a short rear overhang.

As for lifting a coupler off the ball - the only model I can envision so far is that the spring bars' attachment to the A frame don't allow them movement. When a load is applied they push forward on the ball and the pressure could be up and off riding over the ball towards your truck. A DC could aggravate this if the cams were set too far aft. Maybe.

its a puzzle.
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Old 04-08-2006, 09:24 AM   #72
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I wonder if Chuck's dual cam setup might have something to do with his coupler rise that he stated. I do not have that setup, but from the looks of it, the arms of the dual cam might be pushing up the front of the tongue. I would not think this would be a normal thing, but all these things may need to be considered. Looking forward to the results of your test Chuck.
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Old 04-10-2006, 07:43 PM   #73
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Hello to everone,

This is getting technical guys ,newtons theory and all .The tow vehical with heavy sprung suspension such as a 2500 hd chevy will utalize lighter spring bars say 500# this allows for the wanted deflection of the bars. My 68 travelall use the 750# bars ,it has the proper deflection .A 64 travelall towing an airstream with soft rear springs needed the 1000# bars to get the proper deflection. Without the wd sagged down ,level without the trailer .Wd installed , level .The angle of the hitch head leaning back to a point is crucial to the bars of proper rating to level the tow vehical and trailer.It was noted in this discussion about the bars almost touching the ground with the hitch head angled back as is specified in setting up the hitch. Each case will be different ,the hitch head in that application may be back alittle too much. If the ball height is correct on the tow vehical in relation to the coupler height ,with the proper bars tensioned the tow vehical and trailer should be level! If not the setup is incorrect . each application will not be the same and I know I have a travelall .The tension on the bars chained to the A frame under the proper tension will have a pulling down effect as others here have stated . azflycaster has clearly shown it with his test and photos.The reason there is available movement front to rear on each side of the A frame on the snapup brackets is so when you turn right or left the position of your bars will move towards the front or rear. The noise you hear with the reese dual cam snapping in and out when turning ,right? I dont see how the coupler could come up the ball though hmmm.... How about a picture of that .In the WD has a I agree the rear suspension of the VW T or expedition etc, they dont have regular rear springs complemented by airbags .The bags are the rear supension or rather air spring. It is the auto leveling system that I think would be affected .There are level sensors that monitor ride height . I can see that being a problem for sure .The VW T does not approve of any WD setup I believe do they?The last thing I would add is that when properly tensioned spring bars will have a (loaded) upward curve to them towards the A frame ,and if the bars touch the brackets up high and the bars show to much curvature they are too light in# ,need heavier bars . Trial and error to get it right.


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Old 04-10-2006, 08:06 PM   #74
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ME again
Sorry about that garbled sentance in my last post .Dont know how that happened. I forgot to say regarding the bar tension , the upward curvature should not be extreme ,just mild as in a tensioned set if the bars are correctly set up. Sounds like chuck needs lighter bars and it may look like he may not need them but he does . it wont move much and will be like a spring board if jumping on the tounge. It s how it act going down the road . If the truck and trailer seem to ride rough abnormally I agree the bars are too tight.


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Old 10-31-2007, 10:03 PM   #75
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This older thread was brought to my attention due to some questions I posed ["Misconceptions"] (thanks, 2Air).

FWIW, I agree with the premise that trailers need sway control, almost no matter the size. Over the past few months I have been more carefully studying trailers of every sort as we all drive along. It has been rare that, at highway speeds, that I do NOT see trailer sway on even the smallest trailer (short and low, heavy or light load, etc). Even down to portable welders on factory-provided trailers. I am seeing sway constantly.

I do not agree that "heavy truck" and "small trailer" in any way negate this. The comment was made that it was a good thing the Bambi owner had a Suburban. Better, I think, that he had a car pulling this trailer as it has a lower center of gravity, better handling, less rollover propensity, better braking and better power-to-weight ratio. He might not have gotten into the same problem at all. He needn't have fallen asleep to have caught a wheel off the pavement (this is why the highway departments ALWAYS warn of shoulders or medians being closed during construction), just a moment of inattention would have sufficed. I've watched a big rig roll onto its' side -- at city street speed -- because of a 4" curb. With a car the Bambi owner might not have had a problem at all.

Long wheelbase, first; low center of gravity, second. Trucks roll quite easily be they heavy duty (such as Class 8 tractors) or the light duty ones we drive. The light duty ones tend to have their center-of-gravity at/about the top of the transmission bellhousing. Stand outside your truck and measure that point, it is quite high. Recall that, once it starts to go over, that the momentum (height) makes it increasingly hard to stop.

Back to trailers in general: The cheap construction trailers with poor suspensions, and even more poor tires make me think that U-Haul has been right all along: Not for speeds above 45 mph! The only ones which I do not see sway are the small tandem axle dumps (expensive trailers of this type) where plenty of steel seems to provide a non-flexing chassis and decent axles/shock absorbers are doing their job. But I would still add some form of sway control. The "worst" offenders are stock haulers as, like many, I detest the idea of not treating animals well (even those headed to auction); a rollover here is emotionally painful.

Depending on the hitch (for a travel trailer) I still like the idea of balancing out the tongue load (as Andy/Inland RV Ctr points out): 2/3 onto the TV (50/50 FF to RR) and 1/3 back to the TT axles; kept at a constant rate, regardless of conditions (to the extent possible). If that can be achieved by even minor amounts of weight distribution then it would seem to be worth it. If the TV has a front/rear gross WD afterwards that more nearly approaches 50/50, then it would seem that handling is bettered, and the whole rig is better balanced.

And then the proper anti-sway control.

I probably missed something, or maybe made a generalization out of whack. But, just having gotten out of Interstate 35's heavy commercial traffic (and construction with closed shoulders AND medians simultaneously; after dark; three hours to go 126 miles in and then out of Dallas' evening Halloween rush hour), I was glad to have this thread to read and vent back to ordinary atmosperic pressure by an attempt at ordered thinking. Some mighty good stuff up above mine!
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