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Old 09-21-2010, 02:59 PM   #43
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So, are we saying there is a choice between proper weight distribution to the front axle of the tow vehicle and softer ride for the trailer?

It seems to me that the argument for a lighter bar isn't considering what the bar is supposed to be doing.


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Old 09-21-2010, 03:12 PM   #44
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Sean, you appear to be an expert. Would you like to explain the physics and the trade-offs for us?
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Old 09-21-2010, 03:25 PM   #45
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Quote:
Originally Posted by Dave Park View Post
Sean, you appear to be an expert. Would you like to explain the physics and the trade-offs for us?

Don't let appearances fool ya...

I believe weight distribution bars should distribute enough tongue weight to get the front axle of the tow vehicle to near its unhitched weight. If it doesn't do that, the trailer is UNDER-hitched.

The physics have to do with tau=r*F and all that kind of stuff. As an engineer that stuff excites me but I'm not sure it would advance, what seems to me, a very simple fact; The fact that weight distribution hitches are made to distribute tongue weight and not absorb road shock.
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Old 09-21-2010, 03:58 PM   #46
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Ok, so let's do it question and answer style (And note, I'm asking the questions to move the conversation forward, from a position of some knowledge with holes, so I am being a sort of not-very-devilish advocate.)

My understanding is that a WD hitch is a sprung joint, whose purpose is simply to provide some lift to the hitch, so the tow vehicle settles in a more balanced position. This is problematic because of two aspects: the hinge needs to be fully articulated, and the angle of the tow vehicle and trailer can change during driving, which can increase or decease the loading.

Separately, stiff TV suspension can pass shocks and stresses through to the trailer via the hitch, and this is a mixed blessing: softer ride is better for the trailer, but firmer ride is better for handling. Trying to find a happy medium is key to the safety vs. comfort balance.

As you mount the trailer, the rear suspension compresses. Suspension becomes stiffer the more it is loaded down, so weight distribution keeping the trailer near the midrange of its' unloaded height provides the optimum rear axle handling. It also gives the appearance to the TV of "moving the load forward" by transferring some of that load to the front axle.

Trailers have mass, so no matter what, the TV will have a stiffer ride with or without WD, but with WD the right is only stiffened by the mass increase, resistance from the WD hitch itself and the load-induced hardening of the suspension.

Not using WD, the rear TV axles stiffens, and the front axle softens, while also moving to the opposite ends of their travel range.

Therefore, correct WD provides a softer and more poised ride for the TV/trailer combination when compared to the same combination without WD.

Is this correct? Can you expand on any of this? Did I miss anything from the basic "WD/soft ride" discussion?

Separately, there's the sway issue. That's a whole other post.
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Old 09-21-2010, 04:02 PM   #47
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What is the mechanism that allows the nose of the TV to rise without causing extreme stress on the trailer tongue? Is there one?
If the bars are not intended to absorb road shock wouldn't all bars be made at #1400 regardless of trailer size and weight?
I don't disagree with you Sean. In fact I agree with your POV more than most I've read on here. I just plain don't understand how this would not cause damage, or at least tremendous stress on the trailer.

Feel free to answer or not, as I'm sure you have already been through this many times. I will be reading through your old posts to find the answers as well.
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Old 09-21-2010, 04:11 PM   #48
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Viking: The bars are acting as a spring that provides "up to" their rated pounds.

Some people are mislead that spring implies a suspension behavior. It is not, It is a weight canceling behavior. This is achieved by leveraging the trailer against the TV's hitch box.

In theory, the WD assembly should provide the same uplift as the tongue weight of the trailer.

Still, you know what they say: in theory, theory and practice are the same. In practice, they're not.

The first hitch (ha!) i that the WD hitch extends the length of the pivot point back from the tow vehicle, which increases the leverage of the trailer and decreases the tongue weight a little, as it appears to the tow vehicle. The second hitch (haha!) is that the WD assembly can have a mass of 100-200 lbs itself. The TV sees this as additional tongue weight. For a well-balanced vehicle, the bars should be rated so that in their normal position, they provide the same lbs of lift as that whole combination of load we just mentioned.
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Old 09-21-2010, 04:12 PM   #49
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Originally Posted by VIKING View Post
...If the bars are not intended to absorb road shock wouldn't all bars be made at #1400 regardless of trailer size and weight?...
on SOME types of hitches the bars need to FLEX a given minimum in order to engage the sway control...

friction/cam hitches are an example of this...

the manufacture specifies the MINimum flex needed for the cams to function...

r u clear on this?

so a trailer with a mythical 600 lb tongue many not be heavy enough to FLEX the higher rated w/d bars...

but NONE of that has to do with the myth of soft ride...

and almost no one who opt to use UNDERrated bars supports the change with scale readings...

that demonstrate RELOADING of the front/steering axle...

w/d bars do not equal shock/road vibration absorption.

that is the ROLE of axles/tires and structural assembly.
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Old 09-21-2010, 04:21 PM   #50
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Quote:
Originally Posted by VIKING View Post
What is the mechanism that allows the nose of the TV to rise without causing extreme stress on the trailer tongue? Is there one?
If the bars are not intended to absorb road shock wouldn't all bars be made at #1400 regardless of trailer size and weight?
I don't disagree with you Sean. In fact I agree with your POV more than most I've read on here. I just plain don't understand how this would not cause damage, or at least tremendous stress on the trailer.

Feel free to answer or not, as I'm sure you have already been through this many times. I will be reading through your old posts to find the answers as well.
Cheers,
Rich the Viking


I am not saying that a bar cannot be too stiff. What I am saying is that it is a separate issue from weight distribution. I believe the bar has to be strong enough to distribute the required tongue weight to the front axle. A light bar, rated UNDER the tongue weight of the trailer, will not do that. A bar rated at, or slightly above, the tongue weight of the trailer WILL do that.

Is there a significant amount of stress on the trailer frame when the tongue weight is distributed? No doubt about that. However, I think the trailer should be designed to handle that stress. 2Air' pointed out that Airstream does not do that. That's a shame.

I guess the bottom line is that I always size the bar for proper weight distribution before I size the bar for a softer ride for the trailer.
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Old 09-21-2010, 04:26 PM   #51
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The purpose of the weight distribution bar is to restore front axle load, no argument with that.

I understand the problem is when a much larger bar is used than needed to restore that front axle load. And it is so rigid that it cannot flex sufficiently to allow vertical movement at the pivot point.

Something must take up that vertical movement, say when driving over a dip in the approach to a gas station and the front of the truck rises relative to the trailer. It seems to me it is most desirable that flexibility be primarily at the weight distribution bars, rather than the truck frame/receiver or the trailer tongue/frame.

Add to that a truck suspension so stiff, or wheelbase so long, it takes extraordinary tension on the weight distribution bars to restore front axle load.

I would call this combination over hitching. How can this be tested. The scales won't show any problem. Maybe Andy has a point.

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Old 09-21-2010, 04:34 PM   #52
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Quote:
Originally Posted by Dave Park View Post

1...I'm asking the questions to move the conversation forward, from a position of some knowledge with holes...

2...My understanding is that a WD hitch is a sprung joint, whose purpose is simply to provide some lift to the hitch

3...stiff TV suspension can pass shocks and stresses through to the trailer via the hitch, and this is a mixed blessing:

4...softer ride is better for the trailer...

5...so weight distribution keeping the trailer near the midrange of its' unloaded height...

6...provides the optimum rear axle handling.

7...Not using WD, the rear TV axles stiffens, and the front axle softens, while also moving to the opposite ends of their travel range.

8...there's the sway issue. That's a whole other post.
1. i see no evidence of 'some knowledge of holes' rather i c HOLES in the knowledge

2. w/d doesn't provide LIFT at the hitch

(??? if the coupler is LEFT OPEN and w/d bars tensioned, what happens AT THE BALL/CUP???)

3. there is no evidence that stiffness of the tv suspension is passed on 2 the trailer...

in fact there is evidence that this does NOT happen.

http://www.airforums.com/forums/f238...tch-53341.html

4. IF softer were better for the trailer then FLOPPY would seem to be ideal...

define soft in either qualitative OR quantitative terms...

5. gibberish. w/d doesn't KNOW where the 'mid range' of suspension is for the trailer OR the tow vehicle...

6. it's not about REAR axle handling, it's about REloading the steering axle.

7. UNloading the front end doesn't "soften" the front axle, it reduces grip/traction/control at the tire/roadway.

8. SWAY like w/d and bar function has been explained in DETAIL and by some really smart/qualified folks already...

in OTHER threads...

encouraging folks to WASTE keystrokes doing it all over again is disrespecting their (and others) previous efforts...

purely 4 self entertainment.

cheers
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Old 09-21-2010, 04:42 PM   #53
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...Something must take up that vertical movement, say when driving over a dip...
the many references to DIP conjure up images of towing on the rubicon trail....

approach and departure angles LIMIT how and where an a/s can go with regard to dips...

too LITTLE REloading of the steering axle will LOWER the tongue area...thats bad...

TO MUCH (or improper set up) will lower the rear bumper...and that's bad.

but the notion that lighter w/d bars...

ENABLE towing over wild undulations,

is taking the w/d bar flex MYTH to another level of fantasy.

a small/light single axle stream can be ON the ball when OFF the road ...

a 34 footer isn't gonna handle rock/roll regardless of hitch.

try developing REAL situations to explore here, not hypotheticals...

cheers
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Old 09-21-2010, 05:28 PM   #54
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A-frame

I would suggest that those that desire to challenge Airstreams engineering, that they do so,but with the Airstream engineers, not Airstream owners.

Theory's, opinions, ought-to be, not-ought-to-be, should or shouldn't, all make for good conversation.

However, the fact of the matter, converstion "will not" come up with anything more than guess work.

For those that have the genuine interest, contacting and discussing the A-frame issues with Airstream engineers, is the 'only way" to go. Anything short of that, from no matter who, usually stirs up tempers, that sometimes causes hard feelings.

Therefore I suggest that a small group get together, and review the issues with the proper authorities, namely, the folks that designed and built the Airstream trailers.

That, I believe, is the only "for sure" and practical way, to resolve the issues, and without the need for tempers getting off base.

So far, the fingers are pointing at Airstream which is so easy to do, as it "MUST" be their fault, and never the user's fault.

Most certainly, there is more than just a remote interest in this subject.

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Old 09-21-2010, 05:34 PM   #55
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Quote:
Originally Posted by 2airishuman View Post
on SOME types of hitches the bars need to FLEX a given minimum in order to engage the sway control...

friction/cam hitches are an example of this...

the manufacture specifies the MINimum flex needed for the cams to function...

cheers
2air'
2air,

In respect to the Reese Dual Cam hitch, I disagree with the above statement, even if the manufacturer does state it.

The real thing that the Dual Cam hitch needs to work at reducing sway is WEIGHT on the ends of the bars and cams. It's the weight at that point that creates the friction, and the added lift as the trailer turns from straight behind orientation.

Same thing with the Equalizer hitch...it's the weight on the ends of the bars that creates the friction, not the bend.
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Old 09-21-2010, 05:56 PM   #56
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How can you get more real than broken weight distribution bars, bent a frames, broken receivers, popped rivets, stress-torn aluminum . . .

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