5th wheel conversion to gooseneck

[TXiceman]

I am not offering anymore comments or advice on this thread. AS we have noted...it is basic 1st year engineering mechanics. I am sorry that some are offended with my engineering degree, PE license (inactive now) and 43 years of engineering experience.

I will say that there are a lot of products on the market that should not be out there. You can sell anything you can build and market. All you need is a weasel lawyer to write up a warranty which will protect you from product problems.

So it is your trailer or your friends trailer, go ahead and take the chance of damaging it with any sort of GN adapter.

[dbear]

You guys have to admit that this:



Looks completely different than these:



With the Goose Box, it looks like that single triangle created by the two non-Goose Box adapters is split into two by the built-in suspension, one from ball to adapter end to adapter center and one from adapter end to pinbox to trailer frame. Visually it looks like this setup would possibly cause no more stress than a conventional kingpin because the resulting difference in geometry is negligible to my "non-engineer" eyes.



Maybe that's why on their website they say:

"...5th Airborne™ expertise reduces stress transferred to the RV frame...
Independent lab tested & proven to provide a better ride than king pin“bolt-on” adapter solutions (Bosch Automotive Proving Grounds)..."

Gee, look at that. It's not Lippert engineers making the claim after all.

[RustyJC]

The difference in the vertical dimension between the gooseneck ball and a 5th wheel hitch's load plate/kingpin jaws is what creates the higher fore/aft stresses. That additional vertical dimension is present regardless of the type of gooseneck adapter used between the pinbox and gooseneck ball. From a mechanical standpoint, this additional vertical component is like bolting a cheater pipe to the bottom of the pinbox that amplifies the acceleration/deceleration forces transferred to the 5th wheel RV.

A gooseneck trailer is built to handle these higher torque forces - notice all the gusseting in the crown area of the trailer. A 5th wheel doesn't have this gusseting - that's why you see pinboxes torqued off the frame when failure occurs.

Rusty

[caissiel]

Originally Posted by RustyJC

The difference in the vertical dimension between the gooseneck ball and a 5th wheel hitch's load plate/kingpin jaws is what creates the higher fore/aft stresses. That additional vertical dimension is present regardless of the type of gooseneck adapter used between the pinbox and gooseneck ball. From a mechanical standpoint, this additional vertical component is like bolting a cheater pipe to the bottom of the pinbox that amplifies the acceleration/deceleration forces transferred to the 5th wheel RV.

A gooseneck trailer is built to handle these higher torque forces - notice all the gusseting in the crown area of the trailer. A 5th wheel doesn't have this gusseting - that's why you see pinboxes torqued off the frame when failure occurs.

Rusty

I agree with these comments because I did have a pinbox framing failure on my previous 5th wheel
The front beam strength calculations determined that with proper pin loading there was no safety factor left in the steel. I did find the break after being towed by emergency using a GN adapter. In addition the TV was equipped with exhaust breaking. Sitting in the back seat I could see my pinbox flexing everytime the truck slowed down and I begged for the driver to switch of the JB but he never did. It was less then 20 miles around. Hershey PA.

[dbear]

But neither one of you is addressing the design differences of the Goose Box vs simple bolt-on adapters directly. Is it not possible that incorporating the air ride into the adapter at least minimizes those additional acceleration/deceleration forces? Both Lippert and Bosch engineers seem to feel so based upon the data collected during actual product testing.

[RustyJC]

The test was performed at the Bosch proving grounds. It doesn't say that the Goosebox was evaluated by Bosch engineers.

No, the geometry I discussed doesn't change, regardless of the connection between the pinbox and the gooseneck ball. My gooseneck ball on my truck is approximately 3" above the bed floor. The jaws of my 5th wheel hitch are approximately 18" above the bed floor. The significance of this is that the gooseneck ball or the 5th wheel hitch jaws are the point at which the truck applies the forces to accelerate or decelerate the 5th wheel RV. The gooseneck arrangement applies these forces through a longer moment arm, and the truck will apply the same force (Force = mass x acceleration) to accelerate a 16,000 lb 5th wheel from 0 to 60 MPH in 20 seconds (let's say) with either a gooseneck or 5th wheel hitch. Since the torque imposed on the pinbox equals Force x length of moment arm and Force is constant, the longer moment arm is going to impose a higher torque. It has to unless the laws of physics no longer apply.

Even some gooseneck adapter manufacturers are honest enough to recognize this. Although it's masked in marketing speak, look at the following from the Cody Coupler's website (additional emphasis mine):

A word of caution is in order about the use of the Cody Coupler! Because of its design, additional pressure may be placed on the "King Pin" of the trailer it is mounted on. This is a result of the leveraging action involved. Because of this, we feel it is wise to mention several steps that should be taken by the owner of such a rig. These are "common sense" suggestions that could and should apply to any type of trailer hook-up.

REGULARLY INSPECT THE INSTALLATION OF THE COUPLER
Make certain the "King Pin" is securely attached to the Pin Box. Occasionally, additional reinforcement might be advisable.
AVOID THE "POP-A-WHEELY SYNDROME"
Smooth, even starts and stops are always better than the jerky motion.
TRAILER BRAKES SHOULD ALWAYS BE IN GOOD WORKING ORDER!
And properly hooked up.

Air bags and other kluges that work in a fore/aft plane may reduce peak shock loads, but the mean torque applied to the pinbox is always going to be governed by Force x moment arm length, and the gooseneck arrangement is ALWAYS going to have a longer moment arm, thus will apply higher torques than a 5th wheel hitch.

Rusty

[dbear]

Originally Posted by RustyJC

The test was performed at the Bosch proving grounds. It doesn't say that the Goosebox was evaluated by Bosch engineers.

Splitting hairs a little aren't you? Okay, I'll give you they don't specifically say it was Bosch engineers performed the tests, but apparently, "Independent lab tested & proven to provide a better ride than king pin“bolt-on” adapter solutions (Bosch Automotive Proving Grounds)" means something different to you other than independent?

Originally Posted by RustyJC

No, the geometry I discussed doesn't change, regardless of the connection between the pinbox and the gooseneck ball. My gooseneck ball on my truck is approximately 3" above the bed floor. The jaws of my 5th wheel hitch are approximately 18" above the bed floor. The significance of this is that the gooseneck ball or the 5th wheel hitch jaws are the point at which the truck applies the forces to accelerate or decelerate the 5th wheel RV. The gooseneck arrangement applies these forces through a longer moment arm, and the truck will apply the same force (Force = mass x acceleration) to accelerate a 16,000 lb 5th wheel from 0 to 60 MPH in 20 seconds (let's say) with either a gooseneck or 5th wheel hitch. Since the torque imposed on the pinbox equals Force x length of moment arm and Force is constant, the longer moment arm is going to impose a higher torque. It has to unless the laws of physics no longer apply.

So by your logic, all air ride pinboxes, regardless of hitch type, don't do a thing to dissipate any towing forces whatsoever. So any individual who claims to have an improved ride after installing one is sadly mistaken. So it is your opinion too that those engineers are also wrong, or lying?

Originally Posted by RustyJC

Even some gooseneck adapter manufacturers are honest enough to recognize this. Although it's masked in marketing speak, look at the following from the Cody Coupler's website (additional emphasis mine):

Air bags and other kluges that work in a fore/aft plane may reduce peak shock loads, but the mean torque applied to the pinbox is always going to be governed by Force x moment arm length, and the gooseneck arrangement is ALWAYS going to have a longer moment arm, thus will apply higher torques than a 5th wheel hitch.

Rusty

Isn't it the peak forces which are the ones that potentially cause the damage? Which adapters did they have in mind when making this comment? I've seen air ride hitches where the bags at the connection ball, and I can see where they would not do much to lessen torque because of that. However, logically, the location and design of the air suspension inside the Goosebox, between ball and trailer frame, could absorb most of that additional torque by, in effect, creating a different hitch pin point very similar in dimensional relationship as that of a standard 5er king pin to trailer. Consequently, I still maintain until I see some definitive proof otherwise, the design of the Goosebox may be an exception. I would like to know more about their actual testing methods.

[stik]

Originally Posted by kurtdnellson

We are considering moving from a tag along to a 5th wheel. I do not want to sacrifice my truck bed so I was wondering is it feasible to convert a fifth wheel hitch to a gooseneck? Does anyone have information or advice on this?
Thanks in advance.

Well, kurtdnellson, I hope the preceding 34 posts cleared everything up and answered your question!

[RustyJC]

Originally Posted by dbear

Splitting hairs a little aren't you? Okay, I'll give you they don't specifically say it was Bosch engineers performed the tests, but apparently, "Independent lab tested & proven to provide a better ride than king pin“bolt-on” adapter solutions (Bosch Automotive Proving Grounds)" means something different to you other than independent?

No, it just doesn't necessarily mean Bosch engineers, as you stated. A "better ride" has nothing to do with being immune to the failure mechanisms present in gooseneck adapters, however.

Originally Posted by dbear

So by your logic, all air ride pinboxes, regardless of hitch type, don't do a thing to dissipate any towing forces whatsoever. So any individual who claims to have an improved ride after installing one is sadly mistaken. So it is your opinion too that those engineers are also wrong, or lying?

With all respect, you're putting words in my mouth. I never said any such thing. In fact, I specifically stated:

Originally Posted by RustyJC

Air bags and other kluges that work in a fore/aft plane may reduce peak shock loads...

What isn't dissipated is the mean force F. It requires force F to accelerate (A) a given mass (m) to 60 MPH in 20 seconds. F = mA. That mean acceleration force has to be applied to the 5th wheel RV to result in the 20 second acceleration to 60 MPH. Basic physics. The question is, how/where is that force applied? The gooseneck arrangement applies it at the end of a longer moment arm than the 5th wheel hitch.

I have a Demco GlideRide extended pinbox on my 5th wheel, so I'm not trashing the concept of cushioned hitches; just stating that they don't affect mean acceleration/deceleration forces.

Originally Posted by dbear

Isn't it the peak forces which are the ones that potentially cause the damage? Which adapters did they have in mind when making this comment? I've seen air ride hitches where the bags at the connection ball, and I can see where they would not do much to lessen torque because of that. However, logically, the location and design of the air suspension inside the Goosebox, between ball and trailer frame, could absorb most of that additional torque by, in effect, creating a different hitch pin point very similar in dimensional relationship as that of a standard 5er king pin to trailer. Consequently, I still maintain until I see some definitive proof otherwise, the design of the Goosebox may be an exception. I would like to know more about their actual testing methods.

I suspect the higher cyclic torques inherent in gooseneck geometry play a greater role in inducing low cycle fatigue failure in the 5th wheel pinbox/frame attachment areas, but that's supposition based on 40+ years of failure analysis on my part. You seem really sold on the Goosebox despite the basic laws of physics and vector mechanics that apply to it just like any other gooseneck hitch, so I can only wish you the best if you so equip your 5th wheel. I can't see where additional discussion would be fruitful at this point as the subject has been beaten to death.

Rusty

[jesilvas]

Originally Posted by stik

Well, kurtdnellson, I hope the preceding 34 posts cleared everything up and answered your question!

I would think so. They asked for any information and advice.

[TXiceman]

Rusty, you should know by now that some people cannot accept scientific thinking and will only believe magical thinking. This why I backed out of this thread. You and I know better, but some people have made up their mind based on magic.

Ken

[dbear]

Originally Posted by TXiceman

Rusty, you should know by now that some people cannot accept scientific thinking and will only believe magical thinking. This why I backed out of this thread. You and I know better, but some people have made up their mind based on magic.

Ken

So we should only believe the engineers you say we should, simply because you say so. Right.

[jspande]

Originally Posted by dbear

So we should only believe the engineers you say we should, simply because you say so. Right.

Isn't the issue, who do you listen to for an engineering problem (which this obviously is), an engineer or a non-engineer?

[dbear]

Originally Posted by jspande

Isn't the issue, who do you listen to for an engineering problem (which this obviously is), an engineer or a non-engineer?

Ah, but Reese had a group of engineers test the Goosebox, and based upon the results of that, Lippert endorsed it. These are facts.

So it's more an issue of which group of engineers do you listen to? Right now, those two groups are (1) independent engineers who tested the actual product, and (2) some forum posters who claim to be engineers and who have not.

In my opinion, the latter group simply does not have the specific knowledge - i.e. Goosebox design specs, testing procedure and data - to unequivocally disprove Reese's claim. That doesn't mean they couldn't be correct, just that right now, they are not.