How Fifth Wheel Hitches Work


If the fifth wheel hitch is properly installed in the bed of the pickup, the weight of the trailer will press down between the cab of the truck and the rear axle.
If the fifth wheel hitch is properly installed in the bed of the pickup, the weight of the trailer will press down between the cab of the truck and the rear axle.
Jill Fromer/iStockphoto

It's probably not a stretch to suggest that everyone is familiar with the standard semi trailer design. Not only do they tower over nearly every other vehicle on the highway, but they're often the longest vehicles on the road. Big rigs are capable of towing trailers that carry literally tons of cargo weight. But how do they do it?

Sure, semi trucks have gigantic diesel engines, and those have a lot to do with moving that much weight. But how can the vehicle support and hang onto that much trailer weight in the first place? A relatively puny ball hitch -- the type you'd find below the back bumper on any pickup truck, SUV or recreational vehicle -- would snap off under that much weight. So what's the secret?

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There's no real secret, except that semi trucks don't use ball hitches. They rely on a heavy-duty trailer attachment system, one that closely resembles towing equipment you can add to your own heavy-duty pickup truck -- a fifth wheel trailer hitch. Fifth wheel hitches are designed for carrying much heavier loads than the typical ball hitch can handle. The front edge of the trailer extends over the rear bumper of the pickup truck. The attachment point is in the bed of the truck, not at the rear bumper. When properly installed, the weight of the trailer is actually pressing down between the cab of the pickup and the rear axle. This allows the truck to carry a significantly greater amount of weight -- a much larger trailer, in other words.

The fifth wheel hitch (the part that lives in the bed of the pickup truck) is a large, flat plate that has a shape similar to a horseshoe. The metal rails that run beneath the hitch attach to the frame of the pickup truck for strength. The trailer connects to the fifth wheel hitch via a downward-facing pin -- called a king pin -- along with a plate that rests on top of the fifth wheel hitch plate. The king pin locks into position so it is secure within the hitch but can pivot to accommodate turns.

­The flat plate of the trailer and the flat plate of the fifth wheel hitch are in constant contact with one another. They slide against one another continuously when the trailer is in motion, so lubrication between these two components is critical.

­As far as towing equipment pricing goes, fifth wheel hitches run the gamut. They seem to start around $500 for an "economy" fifth wheel hitch and go beyond $3,000 for a top-of-the-line model. As a general rule of thumb, as the gross trailer weight rating of the hitch increases, so does the price. Of course, the high-end hitches also feature various design attributes that make them valuable to someone pulling a heavy trailer. Sliding hitches, better bearings and heavier attachment hardware are just a few examples of features that can drive the price of a hitch upward.

Let's just say that you've decided to install a fifth wheel hitch in the bed of your heavy-duty pickup truck. Will you need to have someone install it, or is it something that you can easily handle on your own? Read the next page and decide for yourself.

Installing Fifth Wheel Hitches

Installing a fifth wheel hitch isn't really all that difficult -- and just look at the size of the trailer you can pull with one, too.
Installing a fifth wheel hitch isn't really all that difficult -- and just look at the size of the trailer you can pull with one, too.
Jill Fromer/iStockphoto

Prior to installing a fifth wheel hitch on your truck, regardless of whether you decide to do it yourself or have it installed by a professional, you must ensure your vehicle is rated to hold the extra weight of the trailer that you're planning to attach. It sounds rather elementary, yet this point is often overlooked. The owner's manual is a good place to start, and if you can't find the information there, make sure to contact the vehicle's manufacturer for a clear answer.

When the hitch is properly installed in the bed of the pickup, it will be positioned so that the weight of the trailer is between the cab of the truck and the rear axle. The installation instructions will give you the exact placement for what the manufacturer considers to be the ­optimum towing position [source: etrailer.com].

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However, you can't simply bolt a fifth wheel hitch to the bed of your truck, attach a trailer and hit the road -- the hitch has to be properly anchored to the frame of the truck first. After all, you're going to be supporting and pulling a lot of weight with a fifth wheel, so it had better be secure. You'll need to install a rail kit, too. The rail kit acts like a foundation for the hitch. The rails attach to brackets that attach to the frame of the truck.

If possible, you should attempt to purchase a complete fifth wheel hitch installation kit that was designed specifically for your vehicle. This will save you a lot of time and frustration, as these custom-fit kits require no drilling or welding. The kits contain all of the hardware you'll need for a basic installation, and the holes in the brackets line up with pre-existing holes in the vehicle's frame. If you buy a universal installation kit, you may find that you'll be required to either drill holes in the vehicle's frame or weld the brackets in place to properly mount the hitch.

Another point to consider during your installation is that the rails that support the fifth wheel hitch should never be installed over a plastic bed liner. Even though the rails will initially secure tightly, the plastic will ultimately disintegrate, leaving you with a loose hitch. If you have a pickup truck with a spray-in bed liner, you're in luck -- fifth wheel hitches can be installed in a bed that has a spray-in bed liner [source: etrailer.com].

If you're able to purchase a custom-fit installation kit, the installation of a fifth wheel hitch requires little more than a good deal of measuring, followed by bolting the brackets and rails to the frame of your truck. With that said, many people opt to tackle this rather uncomplicated installation in their own garage or driveway. Of course, if you are unable to purchase an installation kit that was designed for your specific vehicle, or if you have any reservations about being able to complete this project on your own, you can hire a professional to do the job for you. As long as there are no complications, it won't take a certified mechanic very long to complete the installation of your latest piece of towing equipment. After all, if they're accustomed to installing towing hitches on other tow vehicles, installing a fifth wheel hitch in the bed of a pickup truck shouldn't be all that difficult.

To read more about towing, hitches and other related topics, follow the links on the next page.

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Sources

  • etrailer.com. "Fifth Wheel Hitch Information and Installation Tips." (Oct. 7, 2008) http://www.etrailer.com/faq_fifthwheel.aspx
  • Gray, Scott. "Fifth Wheel Trailer Hitches - For Those Big Loads." Offroaders.com. (Oct. 7, 2008) http://www.offroaders.com/tech/Fifth_Wheel_Trailer_Hitches.htm
  • Gray, Scott. "Fifth Wheel Trailer Hitches - The Strongest Around." Cowboyway.com. (Oct. 7, 2008) http://www.cowboyway.com/What/FifthWheelHitches.htm
  • The Hitch Corner. "5th wheel Hitches." (Oct. 7, 2008) http://www.hitchcorner.com/fifth-wheel-hitch.htm