Thoughts on which hitch to use please.

[s1000pre]

On my first trip out with my Hensley, I questioned if the trailer porpoises more than with the Blue Ox. I disregarded the slight additional porpoising since I was so ecstatic with the sway elimination. I (my opinion only) would gladly endure an extra bounce contacting uneven road, over the constant correcting from wind gusts and passing large vehicles.
When there is a pivot point (hitch ball) connecting the TV & Trailer, the combination of the two will pivot on that point.
Sway is the side-to-side movement you feel when your trailer influences your tow vehicle. Regardless of how perfect you have your WD set-up, you will have sway. The question is how much. If you welded the ball to the hitch, you would eliminate sway. Unfortunately, with a welded ball, you wouldn’t be able to turn your vehicle. The goal with WD is to lessen sway, not eliminate it. When you have your WD hitch ideally set up, your tow vehicle should not have any additional understeer or oversteer when connected to the trailer. It should feel very stable until an outside influence forces the truck/trailer combination to move without TV input. Many choose to use HD tow vehicles married with a WD hitch to counter any outside influence. This combination works very well until this outside influence overcomes the TV and WD combination. The difference with the PP or Hensley is it removes the pivot point between the TV & Trailer. Just like the welded ball concept. Only the PP and Hensley still allows you to turn.
To help reduce fatigue with Fast-moving semi's, windy days/weeks, rogue wind gusts, etc. I went with the Hensley and removed the pivot point. It has been much more relaxing.

[ROBERT CROSS]

^
AGAIN....if you bounce and it's NOT the road, it can be mitigated with a proper lash-up, regardless the hitch.

Bob
🇺🇸

[Silvr_Bullet]

I sense a little back walking here🥸

[pteck]

Thanks for your insight and clarification JCL.

There's no ill will on my part with any of this. There's pro and cons with everything including the Equalizer hitch I personally use. As with any mixed audience, there a lot of unnecessary defensiveness and talking past each other. Not the first time trying to isolate singular points of discussion on a technical topic, only to get wrapped around the axle in understanding. One has to wonder how we ever landed on the moon without confidence in concrete engineering concepts. And the only way is to anecdotally prove things?

Just the same, this is an interesting discussion. Sorry to the OP and this probably deserves its own thread.

[ROBERT CROSS]

Originally Posted by Silvr_Bullet

I sense a little back walking here🥸

Not really. Folks read into it what they want to read into it.
I always said a proper lash-up will not porpoise, (any hitch).

Bob
🇺🇸

[Air Cruiser]

No problem here with the discussion — any and all healthy discussion(s) re: pros/cons of any type hitch is greatly appreciated! We sincerely would like to have as much hands-on knowledge that anyone has learned through trial and error and/or engineering facts learned. I assure you that everything which has been shared will be read, dissected, researched, and used to make our decision. This is a big deal for us and one which we hope to make only once.

Thanks again all.

Deb

[renderit]

I am going to toss in this grenade and duck...

'Porpoising' as I understand it is when the tow vehicle and the trailer rise and fall at the same time inducing shock/spring travel at an uncomfortable level. Indeed; inducing sympathetic rises and falls in an amplifying manner.

Or is that 'bounce'?

If that is the case then 'porpoising' would be more accurately be when the nose of the TV rises as the tongue dips.

This is caused by undulations in the road surface that more or less match the wheelbase of the tow vehicle and the TV/Trailer combo. OR cause the dip/rise syndrome.

As the PP lengthens the wheelbase between the TV and trailer:

Could it not also be said it could correct the problem in some cases as well? As the whole sympathetic bit is entirely dependent on the length of the undulations and the distance between all axels involved?

Does it not depend on the truck wheelbase as well? Crew Cab vs single. 25' trailer vs 27', 30' etc?

When it happens it is disconcerting. I doubt anything makes it worse or better. Short of adjustable wheelbase. Which I don't think will happen soon. (though some semis have it).

I am failing to see how ANY WD system will not exacerbate or alleviate the issue. As is is a geometry/physics question.

Am I missing something?

[renderit]

Ah!

Longer moment arm...

But I gotta say, I drove I-20 thru Shreveport LA and had no problems.

Other than the Burma Road...

[airdreamers]

What is a moment arm?

[jcl]

Originally Posted by airdreamers

What is a moment arm?

The distance from some point (such as the centre of rotation) to where the force is applied. In this discussion the force is acting on the hitch ball, and the moment arm is longer for the PPP hitch because of the extended coupler.

[jcl]

Originally Posted by renderit

This is caused by undulations in the road surface that more or less match the wheelbase of the tow vehicle and the TV/Trailer combo. OR cause the dip/rise syndrome….

When it happens it is disconcerting. I doubt anything makes it worse or better. Short of adjustable wheelbase. Which I don't think will happen soon. (though some semis have it).

Lots of things will impact it. Travel speed. Shock absorber efficacy. WD tuning. Shifting the trailer load to be more over the trailer axles.

Anything that impacts the damping of the system.

The concern with the longer moment arm is that more damping will be required. That isn’t to say that sufficient damping can’t be achieved.

[ROBERT CROSS]

[QUOTE=renderit;2517473]Ah!

Longer moment arm...

But I gotta say, I drove I-20 thru Shreveport LA and had no problems.

Other than the Burma Road...[/QUOTE
><><><><><><><><><><><><<

Every moment counts....👍

Bob
🇺🇸

Another example of a longer moment arm improving towability, safety and POM of the users.👍

[pteck]

Originally Posted by airdreamers

What is a moment arm?

Indeed this is much about an overhung weight creating a moment arm which makes forces harder to control. At the risk of confusing the argument, perhaps an analogy can help.

Imagine carrying a large weight, say a watermelon, on your person. One posture is to carry it closer to the chest. The other is to hold it further at arms length (creating a longer moment arm) for that weight.

Imagine running down the street. Which posture makes it easier to control that weight? Add in an uneven course with undulations, again which is easier to control?

Yes, there's dynamics of watermelon size (tongue weight), individual strength (TV capacity), individual size (TV length), muscle control (suspension and damping), etc.

Sure there's compensations and adjustments one can make. But the reality is that for each of the variables, there's significant geometric advantages to keeping shorter (arms length) overhangs.

[uncle_bob]

Hi

We are talking about two different things here:

Motion in a horizontal plane is one thing. Motion in a vertical plane is something very different. The first one can get you into catastrophic trouble ( = sway). The second one is simply uncomfortable. It is very easy to come up with a horizontal plane "fix" that does absolutely nothing at all for the vertical.

One way to look at vertical plane issues is a resonator. It "rings" at a certain frequency and likely at some harmonics of that frequency. When it rings, it amplifies the input. Change this or change that in the setup, you change the ring point. Go a little faster or a little slower down that road and not so much trouble. The "input" ( bumps ) are not as close to the ring frequency. Vary your speed on the road and ... not so much trouble.

Is that the whole and only explanation, no its not. There *never* is a whole explanation for any real world physical system. You simply don't have the time or the gear to come up with a complete description ( and the thousands of pages to write it down). We deal with simplifications that are "good enough" for this or that instead. The simplification that is good enough for this fix, may not be good enough for another ....

Fun !!

Bob