Warning – this post is kinda long and could be considered a rant.
Just a quick question to the folks here that actually tow a variety of trailers. I have been lurking on the RV.net message boards and one item that seems to always come up is the topic of adapting a fifth wheel trailer to a gooseneck hitch.
I have one on my camper, and I cannot for the life of me understand why anyone would want anything else.
When you read questions posted by other readers on RV.net forums about the same things you get a real hodgepodge of answers. They run the gamut from the really technical (thay will brake ur trailor) to in-depth comparisons to heavy duty equipment hauler trailers. I do have several heavy duty trailers built for gooseneck hitches, and yes they have very stout components to brace the neck. But I guess the main fact that most folks miss is that the camper trailer is NOT designed to haul as much as my other trailers. Heck, the camper only has tandem 3500# Dexters with 15” load range C tires. I think that the bracing in the neck area is more than sufficient for that kind of load (GCVW 7700#). The big show trailer (24’ Hart) has tandem 7200# Dexters (yes they exist, try to find brake parts for them), and the 24’ equipment trailer has 2 – 7K axles. Our bar-top stock trailers have 6K axles. I think that I have experience toting loads.
Could it be that these RV’ers are just biased against the gooseneck hitch since they are unfamiliar with it? I love the way that it does not take up space in the bed when not needed, and I think that the off-road articulation is greater than that even afforded by the new rocker style fifth-wheel hitches. They cost less and are easier to maintain. Maybe you could say that I am biased myself – even though I have hauled using both types of hitches.
I know of e few of my co-workers that have large toyhaulers with the gooseneck adapters, and they say that they were installed by the dealer and will not void the manufacturers warranty. I even see a lot of the “rig-rats” (an endearing term for the gas well workers flooding our area) that use the adapters. In fact, it seems that the split is about even as to those with the adapters and those without.
If you take into consideration the mechanics of using the adapter, it has been pointed out that the could apply loads in directions that the frame structure was not engineered for. I really enjoy the posts that discuss weight and moment loading – as I am familiar with the mechanical engineering aspects of those discussions. The one fact that kills their suppositions is the relative popularity of the extended pin box. This actually transfers the pin weight in an upward arc (moment force) and is no different than using an adapter. In fact, the adapter I use is very well made and takes any horizontal loading forces into account by using a triangular gusset to transfer those forces to the vertical beam.
I guess what I am really asking is: have any of you out there actually seen any damage caused by the use of a fifth-wheel/gooseneck adapter? I truly believe that the posters on the RV forums are only citing anecdotal evidence and have no real experience hauling a variety of different style in-bed hitched trailers.
Dry Creek

 

Yes, 5th wheel frame/pinbox failures have been experienced by a number of individuals, including some on the various Dodge/Cummins forums. Although a few of the RV manufacturers have expressed willingness to design/build a gooseneck configuration, none that I know of (and we've surveyed them) will honor the structural warranty if a gooseneck adapter is used.

Rusty

 

I'm with Rusty on this one also. I always tend to ask RV dealerships concerning these adapters when the wife and I stop just to look. I have not had one yet say that the manufacturers they carry would warranty structural damage from using one. Not to mention, the interior walls are bound to suffer stressing to the point of screws loosening all over the rig. The factory pin box on my Cougar looks to be the same length as the one in the picture above and as far as I know, that is considered an extended pin box. I think Keystone would only warranty one other pin box for my particular trailer which was only 2" longer (which I didn't need anyway). We did have a campground neighbor that had extended his own pin box by 8" and then was wondering why the attached frame work had started cracking all over the place under the nose of his 5er.

Click HERE for one RV owner's experience

 

I personally think that the 5ers might be under-designed for nose strength to begin with as I know of several who use their 5ers a ton more than most people and have problems with the stock designs. There have been many through the years with stress problems, so, maybe there is an inherent problem with the design and the GN stresses makes it more noticable earlier than would be normally seen.

I think we all can relate this type of idea/concept/possibility if we consider the logic about using high performance mods and the rail pressure problems with our trucks. Look at the GN in the same mindset as this, and ultimately it does make more sense regarding the stress related issues that are being considered. Also, it can be related in much the same manner as doing suspension mods and finding out you have a weakness in your driveline articulations.

The 5er industry was originally geared to the person who was 'retiring' and would be only pulling one thing over an extended timeframe, they would be stopping for longer periods of time vrs regular weekend outings. What you could call the 'camper'. Then, most then had 2wd rigs with much less hp and traveled at much slower speeds, etc. The rigs in the overall had less 'road' stress and a lot less mileage.

The GN group of yesterday in the same light of time, were users of horse trailers, flatbeds, and enclosed trailers. They had an entirely different end use. The GN industry became what you could call 'specific' to this group of uses.

Today's users are looking for versatility across the board, they have multiple uses for their trucks, etc. We all try to get the most out of one setup for towing with the same rig. Today's 'hauling' industry is very different than yesterday's and the whole group of hauling manufacturers needs to adapt to todays generation of users.

My real question after all of that discussion is quite simple - Why would the structural 5er trailer design for towing stresses be any better or any less in difference between the two groups? You are towing the same gross weight vehicle (trailer) from the same points of stress regarding weight, aerodynamics, etc. NO ONE has actually studied the hitch point articulations to determine the 'reality' of hitches, ALL of these issues are/have been strictly engineering speculations using geometric calculations. If in fact the 5er hitch is that much better over the GN in it's configuration at the hitch in the bed, then why would the DOT let GN's be out there towing as much, if not more weight down the road due to what could be called safety issues with a less capable hitch?

I personally think that ANY tow vehicle that should be/or is designed for tow stresses and distribution should be able to be used in either configuration, and furthermore the industry needs to get their designs up to this level, period.

CD

 

Both hitch designs have their place. Goosenecks offer greater articulation, but carry the pin load over a much smaller surface area (higher unit loading). 5th wheels utilize a load plate to carry the vertical load and a kingpin to transmit the fore/aft and side-to-side loads - that's why the Class 8 over-the-road rigs use this design. Because of the placement of the articulated joint (much lower on the gooseneck), greater moments (bending forces) are generated with a gooseneck design for a given trailer weight - that's why the gooseneck trailer utilizes more steel in its "crown", and that's why 5th wheel frames can fail when subjected to gooseneck forces. Not that one is better or worse than the other, just designed for different requirements and applications.

If one has to tow both types of trailers, I'd recommend a hitch like the B&W turnoverball gooseneck with the companion 5th wheel RV hitch accessory. I, as well as many others, have used this arrangement successfully for years.

Rusty

 

Good points, all.
Like Rusty JC mentioned, there could be moment (lever effect) forces applied to the pin box mounting locations, but you can engineer those forces away by simply using a gusset (as shown above) to transfer those forces back to the vertical plane.
I know of two manufacturers that offer gooseneck pinboxes for their toyhaulers, but you have to use the one provided by them only. I think most failures that occur would be on the very large fivers using the low budget adapters that merely clamp to the bottom of the pin box (around the pin).
I also believe that many of the camping trailer frames are made just too frail for the loading they receive. RV manufacturers across the board are guilty of underdesigning their frames for the actual loads they see in real life.
Dry Creek

 

This point I believe is due to the fact that they are inherently designed for the internal "guts" if you will, to take up alot of the structural strength loading put on them. This way they can make the units lighter with smaller frames.

Unfortunately, not evreyone runs them only on pavement. This is where the problem arises when one takes these units onto less than ideal off-road situations and applies more structural stress than the manufacturer intended.

Hate to say it, everything is being designed for city folks whom don't leave pavement - take a look at our trucks, or paved campgrounds. If you want something truly "heavy duty" nowadays, you have to have it built, and usually pay for it through the backside as well.

JMHO.