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Old 08-09-2012, 10:42 PM   #57
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Quote:
Originally Posted by tpm64 View Post
i know what I am about to propose goes against most everyone here, but here goes:

Can anyone explain (using real engineering) how adrop set up has different forces (x, y, and torsional) than and angled (non level) tow bar?

I contend that horizontal, vertical, and rotational forces are identical in both cases. That is, drop receivers do nothing to change physics. As an experiment, bend a wire to look like a drop hitch. Lay it on a flat surface. Push the end just like the car is pushing into the back of a motorhome. Does it rotate or slide straight or do some combination? Now take a straight wire whose ends match the ends of the drop hitch and do the same thing. Does it rotate or slide or do some combination? Does it do exactly the same as the prior experiment?
Sorry, I retired from engineering in 1998, well, actually about 10 years before that when I got my AA in computers and went into the IT dept.
I always hated vector stress analysis and stress diagrams anyway!!
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Old 08-10-2012, 08:59 AM   #58
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Originally Posted by Dunner View Post
If I went to WM or even Autozone and asked for a "Ball Mount", what kind of look do you think I'd get? .

I know what you mean though. Sorry for any confusion I may have caused.
For a quick answer, do a google search on each term and see what comes up? Don't mean to pick on you in particular. Others are doing the same thing or similar? (Getting used to arguing with you though. We think along the same lines much of the time)

On these, they're referred to as "drop mounts", as in 6" drop mount or maybe "drop bar"? Obviously they can be flipped to go up, though it's still called a "drop" mount.

Sorry for the side trip, but reading through this, trying to interpret what the poster is saying is a PIA!

I'm no engineer, and no training in stress analysis, but if I could make an "on topic" comment? When considering all this I guess I consider what the results might be in the case of a 30k lb MH which has for one reason or another, come to a very sudden stop.

I think it's a safe bet that 6"-10" drop bar is going to bend under those circumstances, big time. If that happens, all bets are off regarding the tow bar's ability to control the weight behind it. I don't care if the toads brakes are locked up. Now if you're using a 4" drop bar, dunno? Those look pretty sturdy?

On the tow bars that use a trailer ball setup, the coupler would be the weak point. In any scenario where you aren't pulling on that connection, it's not going to take much for it to come off the ball. You have to see that in person to realize how wimpy they are in those cases. I'm guessing a lot of the manf's suggestions to keep the tow bar level come from that issue....

That pic of the hollow broken one? I doubt seriously that happened in toad service. It looks to me like it was bottomed out? If it had been solid it would probably have bent the hitch. -Al
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Old 08-10-2012, 12:00 PM   #59
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Correct and right you are, but to be even more right, add "ball" to your correct term.

6 inch drop mount - Google Search

And also look at the bottom of this page where the hints are.
How many time does the word hitch show up.

6 inch drop mount - Google Search
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Old 08-10-2012, 05:05 PM   #60
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And I think the initial discussion was regarding tow bar / motorhome/ toad set up where no ball is involved...
The adapters that lower or raise the connection from the MH hitch "receiver" are called hi/low "hitches" by the industry...meaning blue ox and roadmaster.
Think this thread has run its course yet?
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Old 08-10-2012, 05:19 PM   #61
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I don't think it matters if there was ball involved in the connection of the tow or not.

I had never seen a receiver or drop mount/hitch failure before and am very glad I saw this thread.

Because of this thread, I will be looking at getting a solid body drop mount/hitch and will be adding a roller to the bottom of whatever drop device I settle on.
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Old 08-10-2012, 07:02 PM   #62
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I have been towing a 09 HHR for three years with a blue ox tow bar without a drop rec and have absolutely have had no problems.
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Old 08-10-2012, 07:56 PM   #63
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We are very close in understanding. What I am contending is that there is no benefit, from a braking standpoint, of a drop hitch over an angled tow bar attached to a toad. And there are problems (striking the ground) with the drop hitch.

Can anyone poke a hole in my proposal?
I re-read your OP and the above post and now think I understand what you are wanting to know.

Is the braking better with a drop hitch or an angled tow bar?

It's been discussed in this or other threads that if the angle is upward towards the coach,
there is a possibility that it will reduce braking on the coach by taking weight off the brake axle.
With a drop hitch, it is pushing straight; with an angle hitch, it is pushing upward as in the drawing.

Is that what you're asking?

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Old 08-10-2012, 09:52 PM   #64
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Originally Posted by Dunner View Post
I re-read your OP and the above post and now think I understand what you are wanting to know.

Is the braking better with a drop hitch or an angled tow bar?

It's been discussed in this or other threads that if the angle is upward towards the coach,
there is a possibility that it will reduce braking on the coach by taking weight off the brake axle.
With a drop hitch, it is pushing straight; with an angle hitch, it is pushing upward as in the drawing.

Is that what you're asking?

Perfect diagram!!!!

I contend that the forces on the TV are identical in your two drawings. The force "pushing" the TV when braking has to be along the line shown on the second sketch. Just because there are a couple of right angles on the first sketch, the force is still along a line formed by the two end points. The draw bar could look like one of those drinking straws with 5 loops in it, and the direction of the forces would still be determined by the two end points.

There may be some other reason to want a drop hitch (geometry of the pivots on the tow arms probably), but there is no basis to say that braking forces are horizontal just because of a drop hitch.
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Old 08-10-2012, 11:15 PM   #65
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You're forgetting that that rear springs on the TV are going to go upward and at the same time the springs on the toad are going to go downward, increasing the angle of the tow bar. That will make it easier to lift the rear of the TV, decreasing the braking of the TV.

With the drop hitch, you are pushing straight forward on the tow bar and the braking will be the same.

If the toad tow bar was higher then the TV hitch, it would push downward, increasing the TVs breaking.

The top of the drop hitch will not pivot, but will on the tow bar.
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Old 08-11-2012, 07:05 PM   #66
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[QUOTE=Dunner;1273034With the drop hitch, you are pushing straight forward on the tow bar and the braking will be the same.[/QUOTE]

Can you show that on a free body diagram of the hitch/tow bar assembly?
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Old 08-11-2012, 07:43 PM   #67
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Good grief!
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Old 08-11-2012, 08:20 PM   #68
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Can you show that on a free body diagram of the hitch/tow bar assembly?
I don't know what you are asking.
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Old 08-11-2012, 08:58 PM   #69
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Old 08-11-2012, 09:35 PM   #70
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