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Old 12-08-2010, 04:17 PM   #29
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I am curious how these tests are being conducted and by whom. To insure accurate and unbiased results, it would be best done by a research lab. No doubt no matter who does what, the results will be questioned and criticized, but by having an independent lab do it, the criticism may be less noisy. After that, what will it mean?

I recall a series of articles in Airstream Life which included information about deflection in bars. I can't say I understood a lot in the articles.

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Old 12-08-2010, 04:24 PM   #30
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Andy,

I look forward to the publication of results.

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I am curious how these tests are being conducted and by whom. To insure accurate and unbiased results, it would be best done by a research lab. No doubt no matter who does what, the results will be questioned and criticized, but by having an independent lab do it, the criticism may be less noisy. After that, what will it mean?
Gene,

The true test of such research is whether the results are repeatable.

Should Andy's results be at odds with our expectations there is always the possibility of re-running the tests. It is not difficult to do, merely time consuming, and requiring access to a platform scale and suitable lifting equipment.
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Old 12-08-2010, 04:41 PM   #31
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Originally Posted by CrawfordGene View Post
I am curious how these tests are being conducted and by whom. To insure accurate and unbiased results, it would be best done by a research lab. No doubt no matter who does what, the results will be questioned and criticized, but by having an independent lab do it, the criticism may be less noisy. After that, what will it mean?

I recall a series of articles in Airstream Life which included information about deflection in bars. I can't say I understood a lot in the articles.

Gene
Everyone is not going to agree with the results of any test regardless of who conducts it. I do believe Andy will give the most unbiased, professional results that will ever be on this site. I am looking forward to seeing the results.
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Old 12-08-2010, 05:10 PM   #32
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Here's what I hope to gleen from Andy's tests (among other things):

I have always been confused what the bar ratings mean. Does 1000# mean the bars a capable of handling 1000#s of tongue weight (max) throughout the operating range (Difference in attitude or angle between the TV and AS, like a steep approach angle)? Whatever that operating range might be...no one can tell me.

Or, does 1000# rating mean that the bars are capable of 1000#s of force on their tip, at max operating range (deflection), before they potentially yield and deform?

I have had this discussion with the folks at Equal-i-zer and we went 'roud and 'round the mulberry bush! (not sure if I'm the monkey or the weesle).

I also wonder at what force 30" rearward of the ball socket (point at thich the "L" brackets mount) would be required before my A-frame yields. Not gonna get that answer, I fear.
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Old 12-08-2010, 06:56 PM   #33
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It appears that Andy is testing various brands & styles of bars, for their rated spring rate vs actual spring rate. I doubt his test procedure will even include a tow vehicle, which would only cloud the results. It would be up to us to take the actual brand/style WD hitch spring rate into account in tuning our towing setup.

Until now the notion that round bars are softer than square bars has been measured by the seat of pants method, which sometimes can be accurate "enough". I want to thank Andy up front for undertaking this work, and I'm looking forward to the results.
I agree with you, just various brands & styles of bars. Nothing like taken a random new part that just came off the manufacture ass'y line and doing a real test, nothing better. The manufactures of these bars do there analysis, build in a safety factor then test them. If the test numbers agree with the analysis that is what will appear on there detailed drawings, hoping that there detailed drawing never appears in a court room of law. I also want to thank Andy up front for undertaking this work, and I'm looking forward to the results.........You rock Andy.

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Old 12-08-2010, 09:08 PM   #34
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Thank you for doing this Andy, and for being willing to share your results.

What ever they are, they will at least be based on actuall tests versus the wet-thumb in the air/best guess we usually have to rely on.

A little Christmas gift for those of us on the forum is it? Regardless, it is very much appreciated.
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Old 12-08-2010, 11:23 PM   #35
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This should be interesting. I'm really interested to see some comparisons with the tow vehicle taken out of the equation. Folks can argue about hitch setups on here until their fingers bleed from typing, but it's all a moot point as long as the nearly infinite combinations of options and tow vehicles are thrown into the mix. It can only be a great addition to the wealth of information archived here. Thanks Andy!
Most of the forum members would have a stroke if I told them I tow my Airstream with nothing but a ball and two safety chains. That is, until you realize the truck weighs twice as much as the trailer, is only a couple of feet shorter than the trailer and still carries considerably more weight on the front axle than the rear while hitched up.
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Old 12-08-2010, 11:47 PM   #36
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Hi, what I would like to see is: How far does a 1,000 lb spring bar have to bend, to have, or hold, 1,000 lbs. And what is the difference in inches, or some other measurement, comparing same rating spring bars from different companies. Also since my set-up has 1,000 lb spring bars, I would assume that, that means each bar is actually 500 lbs.
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Old 12-09-2010, 01:24 AM   #37
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Most of the forum members would have a stroke if I told them I tow my Airstream with nothing but a ball and two safety chains. That is, until you realize the truck weighs twice as much as the trailer, is only a couple of feet shorter than the trailer and still carries considerably more weight on the front axle than the rear while hitched up.
Since you do not use weight distrubution, approximately 50% of the trailer tongue weight will have been removed from the front axle (Weight addded behind the rear axle creates a lever action that removes weight from the front axle.). If you are not carrying enought weight in the bed of your truck to replace the lost weight on the front axle, would you be so kind as to let us know where and when you will be on the highway so that we can take alternative routes.
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Old 12-09-2010, 01:33 AM   #38
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Since you do not use weight distrubution, approximately 50% of the trailer tongue weight will have been removed from the front axle (Weight addded behind the rear axle creates a lever action that removes weight from the front axle.). If you are not carrying enought weight in the bed of your truck to replace the lost weight on the front axle, would you be so kind as to let us know where and when you will be on the highway so that we can take alternative routes.
Errr... you need to compensate for the difference in distance between
the ball and rear axle, and the distance from the rear to the front axle.

If we call L1 the distance from the ball to the rear axle, and WB the wheelbase (distance between axles), we can tell that:

L1/WB * TW = weight removed from front axle.

since the torque (force * distance) has to balance around the rear
axle.

In many cases, this means that the actual effect of 500 lbs of tongue weight is perhaps 100 lbs less weight on the front wheels - less than the effect of carrying a passenger in the front seat.

- Bart
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Old 12-09-2010, 01:56 AM   #39
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I suspect that some of the tapered bars MAY BE a progressive rate setup. We'll see, because this is information that the MFRs have kept close to the vest. I suspect the round bars and square bars which do not taper or change shape along their length out to the tip will be linear in their deflection until the force nears the max. rating of the bar.
This cannot be; deflection of a beam made of a material that obeys Hooke's law is always linear with respect to a defined loading condition. Progressive springs as used in vehicle suspensions typically rely on some of the coils compressing 100% in the case of coil springs in motorcycles, or leaf spring leaves that don't engage until the load reaches a certain point (truck overload springs), or linkages that deflect significantly and change their leverage (mono-shock motorcycle suspensions).


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So much is going to be dependent upon the various alloys used in the spring bars also. I think, in previous discussions we all have a tendency to think all materials used by various MFRs are created equally. Not necessarily so.
All steel alloys have very similar modulus of elasticity, which is what determines deflection per unit of stress.

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Old 12-09-2010, 02:33 AM   #40
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Errr... you need to compensate for the difference in distance between
the ball and rear axle, and the distance from the rear to the front axle.

If we call L1 the distance from the ball to the rear axle, and WB the wheelbase (distance between axles), we can tell that:

L1/WB * TW = weight removed from front axle.

since the torque (force * distance) has to balance around the rear
axle.

In many cases, this means that the actual effect of 500 lbs of tongue weight is perhaps 100 lbs less weight on the front wheels - less than the effect of carrying a passenger in the front seat.

- Bart
So, if we assume that the truck has a 140" wheel base and the ball is 48" behind the rear axle: 48/140*500 = 171 lbs. I think this is a bit more than 100 lbs. What happens if I am not carrying a passenger? If I am carrying a passenger, is the passenger weight distributed between the axles or is it somehow just applied to the front axle?

I suppose that I should have said 30 - 50% depending on the vehicle. I was just trying to make the point that weight distribution provides a safety margin by restoring weight to the front axle, wieght that is lost when weight is added behind the rear axle. Weight lost from the front axle means less reliable steering! I have seen to many trailers off the road or jack-knifed because of severe side winds or slipery conditions and in every case (that I have seen) the tow vehicle did not have a weight distribution hitch. Could the accident have been prevented by using weight distribution? I do not know, but, I do know that my rig is set up with the weight properly distributed between the axles. I like my wife, dogs and trailer to much to take a chance.
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Old 12-09-2010, 04:13 AM   #41
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Originally Posted by Journalist View Post
This should be interesting. I'm really interested to see some comparisons with the tow vehicle taken out of the equation. Folks can argue about hitch setups on here until their fingers bleed from typing, but it's all a moot point as long as the nearly infinite combinations of options and tow vehicles are thrown into the mix. It can only be a great addition to the wealth of information archived here. Thanks Andy!
Most of the forum members would have a stroke if I told them I tow my Airstream with nothing but a ball and two safety chains. That is, until you realize the truck weighs twice as much as the trailer, is only a couple of feet shorter than the trailer and still carries considerably more weight on the front axle than the rear while hitched up.
You have plenty weight on your front tires when your trailer is hooked up im sure. Passengers and gear add even more.
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Old 12-09-2010, 04:26 AM   #42
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I apologize for the disruption my question has caused. It was not my intent to hijack the thread. I thought the question was closely related to the subject. But clearly a lot of people are mad.

So, Andy and everyone, please accept my apology. Andy, I am always impressed with your devotion to the Airstream community and I am very grateful for the contribution you are making with this research. I look forward to the results, as I'm sure do many other readers.
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