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Old 06-23-2006, 05:59 PM   #29
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Originally Posted by bhayden
Did the accident investigation prove these devices caused the accident or is it just that these conditions were present when investigating the accident? I find it very hard to believe "excessive speed", (road conditions, ice, wind, etc.), driver error (quick lane change, drifting off on the shoulder), or mechanical failure (tire blowout, worn steering components..) were never found to be the cause. Who'd 'ave thuk it

-Bernie
Physics proves the point.

As you increase the air pressure in the air bags or air lifts, it progressivley reduces the job for the torsion bars.

When you reduce the bend in the bars, because you have added an overload spring, or inflating an air device, then the bars transfer less weight, rendering the torsion bars progressively useless.

Think about it. If you artificially hold up the rear of the tow vehicle, the torsion bars don't have much of a job to do.

Additionally, when you increase the strength of the "fulcrum", the hitch transfers less weight therefore you add an excessive amount of weight to the rear of the tow vehicle, PLUS, you have removed weight from the front axle of the tow vehicle.

Perfect situation for a loss of control encounter.

Believe or not, your choice, but facts are facts.

Physics tells it like it is, which does not always agree with opinions., or hard to believe's.

I posted that there were other causes for accidents, but the rear end subject caused almost 70 percent of the loss of control accidents. Of course there were other causes, most of which, incidentally, could have also be avoided.

Generally speaking, owners who maximize safety, seldom ever have a problem. Speaks for itself.

Andy
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Old 06-23-2006, 07:16 PM   #30
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Originally Posted by Inland RV Center, In
As you increase the air pressure in the air bags or air lifts, it progressivley reduces the job for the torsion bars.
Not really. If you stiffen or raise the rear prior to loading the hitch then yes you need less tension on the bars to "level" the TV. However, it has basicly NO effect on the actual axle loading and as you point out the front of the vehicle will be light. If you set the tension to balance the weight (harder to do by measuring if you've overly stiffened the rear) then tension and load will be the same. I would heartilly agree that most peoples attempts to reengineer their suspension with air shocks or helper springs has a negative effect. For one thing a leave spring is designed to work best when it's flat. Air shocks are designed to do just that. That's also the job of the WD hitch. Air shocks could fine tune this BUT it's going to be a delicate balance. If you load up the old station wagon and then use the air assist to level out the suspension PRIOR to hitching up the trailer then you should be OK. Of course nothing is going to correct the situation if you've severely overloaded the TV to start with.
Quote:
Think about it. If you artificially hold up the rear of the tow vehicle, the torsion bars don't have much of a job to do.
Draw a force diagram. Stiffening the rear suspension doesn't effect the job of the torsion bars. In fact if you add air to an airbag or air shock AFTER you hitch up the load on the torsion bars will increase (the opposite of what happens by raising the hitch with the trailer jack). If you tension the bars to restore the front rear height ratio the rig had before adding the tongue weight then you've evened out the weight distribution. If you raised the rear with air shocks then it will be raised back to that attitude. That's not good but probably better than being way light in the front with a vehicle that is oversprung in the rear.
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Additionally, when you increase the strength of the "fulcrum", the hitch transfers less weight therefore you add an excessive amount of weight to the rear of the tow vehicle, PLUS, you have removed weight from the front axle of the tow vehicle.
You've lost me here, increase the strength of what "fulcrum"? Spring rates have some effect but the position they settle into isn't going to change the moment arm appreciably. The total weight the hitch transfers to the vehicle is the same. The distribution front to rear is basicly the same. Draw a force diagram. It APPEARS there is less load on the rear and if that's what people use to tension the bars then it will result in insufficient front axle loading.

For a explanation of the physics this post by nickcrowhurst is very good:
http://www.airforums.com/forum...sis-19236.html
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Old 06-23-2006, 07:22 PM   #31
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bhayden

If what you say is true, then Airstream and Caravanner Insurance wasted a ton of money.

Please prove the point your trying to make, buy showing test data from a truck scale.

Andy
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Old 06-23-2006, 08:43 PM   #32
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Mea Culpa

Quote:
Originally Posted by bhayden
In fact if you add air to an airbag or air shock AFTER you hitch up the load on the torsion bars will increase
Oops, that's just plain wrong. Let's say you start out with the trailer and TV level, that is to say that there's neither a V or a ^ stituation at the hitch looking from the side ("hitch down" it would be a shallow V, hitch high would be a slight ^).

Assumptions:
* The angle of the torsion bars is fixed at the hitch, lets call this 120 degrees from the TV around to the axis of the torsion bars (greatly exagerated but the principle is the same).
* In the "level" condition there is 180 degree angle between the frame of the trailer and the TV
* That leaves a 60 degree angle between the axis of the torsion bars and the trailer (360 degrees in a circle)

Starting in the level position and raising the back of the TV creates a ^ as viewed from the side. That means the angle is now greater than 180 between the TV and trailer. Again, greatly exagerated for effect lets say this angle is now 200 degrees. We made the assumption that the torsion bar angle at the hitch is fixed (a close approximation, that's what they're designed to do). This means the angle between the trailer and the torsion bars is only 40 degrees (360-200-60). A smaller angle means you've shortened the distance between the ends of the bars and the attachment to the trailer; therefore you've decreased the tension.

The same think holds true irregardless of what the starting condition is, =, ^ or V. Raising the back with airshocks always shortens the distance between the ends of the torsion bars and the frame of the trailer. If you have a load leveling system on your vehicle you should be able to use it to help unweight the bars when you're unhooking to test this.

-Bernie
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Old 06-23-2006, 09:11 PM   #33
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The bars push downward on the cam followers mounted to the trailer. This is the force that generates the torque moment to push the front of the TV down. Using the trailer tongue jack to raise the front of the trailer and the back of the TV is what many people do to make it easier to hitch up the bars. You could also do the air bags or the pressurized shocks to to the same thing. This does mean the inflation of the air shocks after the unit is hitched up will raise the rear of the TV and will reduce the force on the bars and thereby decrease some of the load that was supposed to be transferred to the front wheels. Net result: Inflate your shocks before you hitch up and disable the ability to have the system readjust itself when you are on the road. I do believe that Andy's figures do not reflect what I know from the number of sway and run off the road or overturn the rig accidents I have recorded in my 12 years with the club. Most people were driving too fast for the conditions or their age. Many of the turn-over accidents have been coming down a hill too fast and the trailer tries to steer or pass the TV. Quite a few of the accidents occurred in road construction when the rig was trying to navigate a very narrow area and there were abrupt lane changes that the people were taking too fast. Two of the turn-overs were due to high wind shear when imerging from between two mountains and another coming out from wind disipating trees and entering a high cross wind. Getting sleepy was the cause for two more leave the road accidents. Bow waves from passing trucks caused two more. The stability of the rig might be part of a number these accidents but the majority of the fault lays with the drivers and road conditions.
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Old 06-23-2006, 09:23 PM   #34
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Quote:
Originally Posted by dwightdi
Two of the turn-overs were due to high wind shear when imerging from between two mountains and another coming out from wind disipating trees and entering a high cross wind.
When traveling along highways that have been logged really really be aware of this. The wind shear along clear cuts can be severe. If there are high winds this is also a prime spot for trees to fall across the road. The wind shear causes a torque on the tree trunks and they literally explode. This is common in Washington forests. Logging companies also have a tendency to leave a small number of trees along the road. Don't know if this is because the timber is on government own right of way or if it's to mask the visual effect of the logging. The problem is the trees no longer have the support of the forest that was around them which makes them prime candidates for falling across the road. Ask me how I know

-Bernie
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Old 06-23-2006, 09:43 PM   #35
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Quote:
Originally Posted by bhayden
In the end that's what you're looking for. You should stay within the guidelines provided by the equipment manufacturer but the optimal setting is going to depend on your individual set-up. Reese can only do so much with their generic instructions. You may in fact be getting little or no benifit from the Dual Cam sway control. It sounds like lighter bars would help. Just driving down the highway you don't have a sway condition but if you get passed by a convoy of semi's and find the trailer oscillating back and forth it's a little late to get out and adjust the hitch. You have such a low WD requirement it might not be possible to get the Dual Cam system to work regardless of which bars you buy (shorter bars will result in more tension for the same WD effect). The oldfashion friction dampener doesn't rely on the load in the bars. Generally it's not considered as good because it works to dampen sway rather than prevent it from occuring in the first place. But if you can't put enough load on the bars without moving too much weight to the front axle then it's probalby not doing it's job anyway.



You've got a light trailer and a decent margin on towing capacity. OTOH, it is a single axle trailer and the lighter the trailer the more it's affected by wind and to some extend road conditions. I'd want to do everything to get it close to optimum. Some of that is just going to involve driving. If you can drive down the road and not feel the trailer (and you can see it's not waving around like a kite in the wind) then you're pretty darn close.
bhayden, my Envoy is a XL, longer wheel base, I live in the Motor City area and will be going down I-94 tomorrow on our first camping trip, lots of trucks, so if I feel swaying then what you are saying is maybe to go to a lighter bar, I will consider wind condition, and if that is the case, I will.....
I will.............
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Old 06-24-2006, 01:52 AM   #36
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Hello all ,

I have read all the postings related to the WD here .The air shocks are a big NO. Why ,? because they are not a spring ,that is designed to lift or hold up the vehical .Yes they make them and on my 64 chevy ll nova I had them on it for some ...."attitude" .they are not designed to lift a vehical then add 500# of weight to the rear axle ,tongue weight. They are kinda of a poor mans lift .The air bag is a substantial improvement over the shock idea .Still
it isn't a leaf spring or coil spring either .In hitching my 68 travelall to the
tradewind ,I raise the trailer with the tongue jack ,hitch ,then install the
bars ,750# in my application to 6 links tensioned .I then let the jack down
and check it over .The tv and trailer are level ,and that is the MOST
important part of the whole WD business because if they are level (not 1"
down in the rear etc etc,) the loading of the frames of both tv and trailer
has been accomplished .The WD when hitched and loaded right ,there won,t be up in front ,or sagging rear or a need for any airbags .The principle is to use the weight distribution to level both the tv and trailer .The spring bars should have upward curvature too them when loaded ,about 1" min too 2"
as Andy has said exactly .Using the tongue jack is perfect for getting the
trailer hitched then leave it raised till you have the bars and chains sinched up in place .Let it down and again check to see if things are level .If not
raise up the trailer /tv with the jack and reset bar tension .If the curve when level is extreme on the upward curvature of your bars ,they are too weak
for the application ,you will need to go higher .If not much curvature ,
bars are too heavy ,go lighter bars .That installed curvature tells you the
tension the bars are under ,easy to see .This business about too much weight on the front axle ? Well ,make sure your tv and trailer are level ,thats the key .By the way I don't think I would do a sway test on the freeway
with semi's blowing by ,unless you want trouble .Hitch it up and look at the bars ,on the reese ,the bars will have some upward bend to them if loaded
right ,if not they will not help the sway ,the tension is needed for them to
work .Back to the air shock deal ,The WD is what you use to level out your
tv and trailer .If you try to raise the vehical to take tension off the bars,
thats totally the wrong approach to correctly use the WD ,argue it or not .
What I like about my none reese hitch is all the bars are the same length
but different # pound ratings ,not shorter .If the lightest reese bars are
too stiff ,somthing isn't working right with the vehical tv or trailer setup.
How about too small a tv or not enough tongue weight .That really needs to be adressed before putting on air shocks .

Scott
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Old 06-24-2006, 07:52 AM   #37
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so if I am looking a t.vs and some were previously used with a fifth wheel...they will have overload springs. This is a no no for a 3/4 ton truck pulling a 31 AS? (Confused)
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Old 06-24-2006, 08:48 AM   #38
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This type of truck will be overkill for an Airstream and will shake it to death. I have seen several people pulling with a heavy duty stake truck or a converted semi tractor. I do not know how they have modified them to make them compatible.
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Old 06-24-2006, 11:11 AM   #39
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bhayden.

The point remains on the table.

Theories, formulas etc, cannot dispute truck scale readings.

Do the homework, as others have pointed out, and get "all" the weights.

Then you will see what we saw hundreds of times.

If I understand you correctly, your suggesting that all of the actual weight data we obtained, is phony?

Andy
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Old 06-24-2006, 12:30 PM   #40
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Quote:
Originally Posted by Inland RV Center, In
If I understand you correctly, your suggesting that all of the actual weight data we obtained, is phony?
Not at all, in fact we're in violet agreement on the end result. My point is that a stiffer suspension does not in and of itself result in more weight on the rear axle or interfere with the way the WD hitch works. Beat up the trailer and adversly effect handling of the TV yes; in most cases.

When you hitch up a vehicle the front will rise. Tension on the bars will bring the nose back down. If you want even wieght distribution on the front and rear axle both wheel wells (or bumpers) will end up lower than before you added the tongue weight of the trailer. If you stiffened the rear it will sink less. If you've really gone overboard it may be almost inperceivable but it does have to go down some. The rig will look "goofy" and handle poorly although probably not AS poorly as if the front end is left light.

I don't see anything wrong with a well engineered load leveling system being used to adjust a TV BEFORE the hitch weight is added. I agree that it should not be used to compete with the job the WD hitch is designed to do.

I'd be interested to know more about the insurance company study. I do find it hard to believe that excess speed was not statisticly significant when every other piece of information I've seen (granted not trailer specific) points to excessive speed being the number one factor in crashes. I was personally involved in one court case involving a fatality accident and "expert witnesses" on the two sides had radically different interpretations of the evidence. Insurance companies hire crash reconstruction experts to prove a conclusion that best suits their interests. The study you reference may well have been an attempt to educate customers and reduce claims (a very economically sound reason to sponsor a study) or it may have been a way to avoid payment by "proving" the accident was the fault of the customer by modifing or incorrectly using the equipment. Either way I still find it hard to believe speed, driver error and road conditions aren't even mentioned.
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Old 06-24-2006, 12:35 PM   #41
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I did list other causes in post # 29.

I posted that there were other causes for accidents, but the rear end subject caused almost 70 percent of the loss of control accidents. Of course there were other causes, most of which, incidentally, could have also be avoided.

Andy
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Old 06-24-2006, 05:50 PM   #42
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Sounds like the study was design and conducted to prove their preconceived point that it wasn't the design of the trailer hitch that caused the problem but was caused by the changes the customer did to modify the suspension of the TV. That may be a valid conclusion but,it does not reflect what I have seen as causing the majority of trailer accidents that actually occur on the roads. Statistics do not lie but sometimes, (for a price) statisticians can make the numbers say anything the customer wants.
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