How to Turn Your Gooseneck Trailer into a Fifth Wheel


PopUp GN5 king pin adapter connected to fifth wheel hitch receiver

When it comes to pulling the heaviest trailers with a pickup, you’re likely going to need a fifth wheel or gooseneck hitch to maximize towing capability. But it can be difficult and time consuming if you have to swap out hitches when you change trailer types, as we found out last year during one of our tests. For this situation, we used a PopUp GN5 gooseneck-to-fifth-wheel trailer adapter.

With the GN5 adapter, it took us less than two minutes to modify a gooseneck Cimarron horse trailer so it would work with a fifth wheel hitch.

Before we describe how it works, though, here’s a quick primer on the difference between heavy trailer hitch types.

Bulldog gooseneck hitch

A fifth-wheel or gooseneck hitch relocates the point of truck-to-trailer contact from the conventional rear bumper position to a more centralized spot in the truck's cargo box, most often over the rear axle. This places a larger portion of the mass of a heavier trailer onto the truck’s suspension, via the trailer’s tongue or king pin.

If you’ve ever ridden in a heavy-duty pickup and commented about the stiff ride, such as with a GM or Ram 2500 or 3500 rig or a Ford F-250 or F-350, now you understand why. These trucks are designed to handle a heavy trailer, with the load either handled by a weight-distributing hitch or a fifth-wheel attached directly to the frame.

Even though they function similarly, gooseneck and fifth wheel hitches use very different hardware. A fifth-wheel receiver looks like a giant horseshoe. It’s the same style of device you’ll find on the back of an 18-wheeler semi. A gooseneck hitch looks like a conventional trailer receiver ball mounted on a plate in the bed.

PopUp GN5 fifth wheel adapter (left) and Bulldog gooseneck hitch (right)

In the case of our Cimarron trailer, its hitch featured an open housing that allowed us to slide out a Bulldog gooseneck coupler and slide in the GN5 fifth wheel adapter, so we could hook up the Cimarron to the fifth wheel in the back of the truck we were testing. Since the GN5 was machined with four holes, we could adjust its height to align perfectly with the fifth wheel hitch in the back of the truck. It’s sturdy, too, weighing in at about 41 pounds.

The best part? Having the GN5 on hand meant we could tow both the Cimarron gooseneck and a Dutchmen fifth-wheel RV without having to swap out cargo box receivers. It costs about $160, but that’s money well spent on time saved.


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