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Old 11-13-2010, 07:03 PM   #29
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Steve,

Trunnion are stiffer than roound bars??? This really makes no sense!!! I believe that stiffness is a function of the cross section, the taper and the material used. Only the engineers can tell us which bars are stiffer although I do believe that a 1000 lb round bar is probably stiffer than an 800 lb trunnion bar.

Everyone,

This thread seems to be degrading into a pissing contest. Maybe we should just concentrate on helping tiger get setup with a weight distrubution system with or without sway control.
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Old 11-13-2010, 07:10 PM   #30
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I think that they are talking about the 90 degree bend in the round bars. Because there is a bend in the round bars, the author claims that this could a weak point in the design.
Yep, that is exactly what the author is saying, if you do a FEA on that bar your hot spot would be that radius.

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Old 11-13-2010, 07:47 PM   #31
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SteveH


Obviously the two of you disagree with me.

That's your choice.

However, I will not engage in any form of arguing with either of you. I frankly have far better things to do.

This Forums has been peaceful and quiet, and I intend to do my share to keep it that way.

Andy
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Old 11-13-2010, 07:47 PM   #32
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I appreciate all the feed back but my head is spinning.

PJohnson said it. "This thread seems to be degrading into a pissing contest. Maybe we should just concentrate on helping tiger get setup with a weight distrubution system with or without sway control".

Please tell me what WD and sway system you have and I will use that to make my decision.
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Old 11-13-2010, 07:51 PM   #33
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Originally Posted by tiger View Post
I appreciate all the feed back but my head is spinning.

PJohnson said it. "This thread seems to be degrading into a pissing contest. Maybe we should just concentrate on helping tiger get setup with a weight distrubution system with or without sway control".

Please tell me what WD and sway system you have and I will use that to make my decision.
Tiger.

Your trailer has a moderate tongue weight. Your tow vehicle boarderlines on heavy duty.

I would suggest a full torsion type sway control load equalizing hitch with a rating of 600 pounds.

Andy
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Old 11-13-2010, 08:04 PM   #34
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Exclamation Do what the manufacturer of your hitch tells you to.

Quote:
Originally Posted by tiger View Post
I appreciate all the feed back but my head is spinning.

PJohnson said it. "This thread seems to be degrading into a pissing contest. Maybe we should just concentrate on helping tiger get setup with a weight distrubution system with or without sway control".

Please tell me what WD and sway system you have and I will use that to make my decision.
It is really quite simple. You look up the max tongue weight of your trailer and then you get lightest rated bar that is equal to or greater than that.

That is exactly what I did, and it is what any hitch manufacturer will tell you to do.

If you want to be certain about your hitch weight buy one of these. It is not that much to pay for peace of mind.

Sherline Trailer Tongue Weight Scales

There are people here that will tell you to get a bar rated for lighter than your tongue weight if you have a 3/4T or larger truck. Follow that advice if you wish, but keep in mind that the hitch manufacturer is not going to stand behind its product if you don't stay within its rating.

Also keep in mind that you will not find that advice (to use a lighter bar) anywhere else but on this forum, and the original source is one person. Anyone else who tells you to use a lighter bar got that idea from this person.

Please talk to the company that manufacturered your hitch.

Regards,

Ken
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Old 11-13-2010, 08:25 PM   #35
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Tiger,

As others have said, you will need to get the tongue weight of your trailer fully loaded. Then, add any weight that will be in your tow vehicle behind the rear axle. Next choose a weight distrubution system with a rating that is greater than your calculated weight (try to get as close to the calculated weight as possible).

We use the Reese Strait-Line setup which is a weight distrubution system with dual cam sway control. Since the tongue weight of our full loaded Airstream is approximately 870 lbs and we have approximately 100 lbs behind the rear axle of our tow vehicle (back part of the canopy + a generator), we need a weight distrubution setup that will handle 970 lbs. Therefore, we chose the Reese system rated at 1200 lbs.
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Old 11-13-2010, 09:31 PM   #36
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Originally Posted by PJohnson View Post
Steve,

Trunnion are stiffer than roound bars??? This really makes no sense!!! I believe that stiffness is a function of the cross section, the taper and the material used. Only the engineers can tell us which bars are stiffer although I do believe that a 1000 lb round bar is probably stiffer than an 800 lb trunnion bar.
Yes, it does make sense...the round bars are tapered to the point they are flat in the middle and very flat on the end very much like a leaf spring. The trunion bars are not tapered anywhere near as much.

Just do some observation on your own...look at a set of trunion bars stressed to point of carrying their aproximate design weight, and look at a pair of round bars in the same situation. Anyone with an open mind can easily see the difference. But yes, you need to have an open mind.

I'm out of this one.
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Old 11-13-2010, 10:35 PM   #37
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I'm also having a hard time understanding why round bars would be more flexible than square bars. Perhaps you are thinking of the Equalizer brand square bars which aren't tapered. .

The Reese trunnion bars I have are more tapered than my round bars. I'm pretty open minded but not convinced there is an inherent difference.
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Old 11-14-2010, 05:40 AM   #38
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How many thousands of miles have you towed your Airstream in the last year, what type hitch did you use, what tow vehicle, how many states did you tow in, on what type roads, do you even own an Airstream?
Take it easy Steve, Andy has forgotten more than you and I together know about airstreams.....
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Old 11-14-2010, 08:38 AM   #39
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I'm also having a hard time understanding why round bars would be more flexible than square bars. Perhaps you are thinking of the Equalizer brand square bars which aren't tapered. .

The Reese trunnion bars I have are more tapered than my round bars. I'm pretty open minded but not convinced there is an inherent difference.
Markdoane, the below pictures are of 800lb and 1200lb trunnion bars with dim's.

toastie
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Old 11-14-2010, 09:16 AM   #40
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Found this on RVNET and the question was "has anyone actually measured or calculated the forces at the end of the bars where it locks into the cams of the sway control as well as at the head?"

In my conversations with Reese the sticker rating is a limit to what the WD bar can be used for in the combination of hitch weight and extra truck cargo weight aft of the rear axle. The 1,200 rating means it can be used at 1,200# and not be an issue. They will not warrant it over 1,200#. Now they did not get into tolerances and generally speaking 1,201# is not going to break the bank. However if you start pushing 1,250 to 1300 and up, the effectiveness of being able to transfer the weight within the degrees of head tilt, chain links and other adjustment is no longer in check.

When you go into a turn the inside WD bar unloads to zero if the truck is on much of an angle. So the outside WD bar is taking all the load. That is where the high forces come into play. Turns. When the TV and TT are straight ahead each bar takes half the load. In a turn, 1 WD can easily take all of it.

Your question on WD bar force. Ron Gratz who did the sticky is into the calculations big time and his assumptions I have found to be sound. I actually set out to try and measure the loads however the setup was not totally correct so my force values where not as high as Ron’s.





And the test values that are not totally correct. But in the “league” seen. Error can be up to 15 to 20%.
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Old 11-14-2010, 09:48 AM   #41
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I've done similar studies with my Reese 600 lb bars and Draw-Tite 800 lb bars. In my study I used deadweight loads on the bars and calculated deflection in lbs/inch.

Here are the summarized results:

Bar dimensions (mean of two bars):

Reese 600 lb bars:
thickness at head end 1.136"
thickness at taper end 0.599"
taper 0.0302"/inch

Draw-tite 800 lb bars:
thickness at head end 1.132"
thickness at taper end 0.645"
taper 0.0271"/inch

The spring rates for single bars are:

Reese 600 lb bars: 179 lbs/inch
Draw-Tite 800 lb bars: 195 lbs/inch

It's pretty easy to calculate the centering force using these rates and the dimensions of the cam follower on the Reese Dual Cam set-up, along with the angle between the tow vehicle and the trailer.

There doesn't appear to be that much difference between the bars. I think this is probably due to manufacturing variations. It's possible that if I checked another set of bars the ratings would be 10% higher or lower.
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Old 11-14-2010, 09:57 AM   #42
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It's pretty easy to calculate the centering force using these rates and the dimensions of the cam follower on the Reese Dual Cam set-up, along with the angle between the tow vehicle and the trailer.

There doesn't appear to be that much difference between the bars. I think this is probably due to manufacturing variations. It's possible that if I checked another set of bars the ratings would be 10% higher or lower.
On your setup, what head angle did you use?...........toastie
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