5th Wheel Of A Semi Truck

semi-truck-5th wheel


A semi-truck is called by many names, such as semi, semi-trailer, 18-wheelers, semi-trailer trucks, or semi-trucks. A semi-truck is made up of two components. The first part is that of a truck with an engine that drives the trailer. The second part is the trailer, which contains a heavy load.

A semi-truck usually carries large loads from one point to another. This load is carried in containers sitting on the back of the trailer component. This component is attached to the truck, so it can be driven easily. 

Read further to learn about the fifth wheel of a semi-truck.

What Is A Fifth Wheel Of A Semi Truck?

The fifth wheel of a semi-truck is a component that attaches the two parts; hence it is named a wheel but is not a wheel. The fifth wheel has two components; the male and the female component. The truck has a kingpin plate that holds the kingpin- the male part while the fifth wheel is the female part.

Both the parts are connected so that the tractor connection can move together with the truck and easily turn. To have a smooth connection, many different forms of lubrication are used so that the parts don’t undergo wear and tear. Lithium EP is the most recommended lubrication, an example of high-pressure grease.

Why Is It Called A Fifth Wheel?

The name fifth wheel is related to its history. Similar designs of a fifth wheel have been in use since the 1850s when horses were the main source of transportation. Martin’s fifth wheel company in early 1900 was the one responsible for the introduction of fifth wheels as an amazing discovery. And as a result, the company named its latest invention after their name “The Fifth Wheel.”

After the era of the horses, the truck came into use, and hinges were used to connect the cargo. The numerous bumps on the uneven roads caused a large effect of wear and tear on these hinges. The kingpin was then introduced in the shape of a wheel which was then made in a protruding shape allowing the fifth wheel to attach to it comfortably. Since then, the fifth wheel has been one of the most important components of any trailer or tractor.

Why Is A Fifth Wheel Used?

A fifth wheel is a component that can be added to the bed of a trailer, tractor, or other similar large vehicles. It is a u-shaped hitch normally used to carry large loads and cargo and helps distribute the weight equally along the whole vehicle. 

The fifth wheel allows the front axles of the trailer to be moved freely while tagging the uniformly distributed weight along with it. It is one of the safest and most revolutionary methods to carry and transport cargo easily and effortlessly.

What Is A Kingpin?

The fifth wheel connection’s kingpin, an essential component, serves as the hinge between the tractor and semi-trailer. The kingpin setting, which impacts the vehicle’s turning radius, is the distance between the centers of the fifth wheel connection and the rear axle group. A truck’s steering axle and steering knuckle are connected by the kingpin, ensuring the steering geometry and enabling the wheel end to turn the truck.

In order to ensure a safe journey, it is critical to ensure the best condition of the kingpin, that it is not worn out and properly lubricated. The kingpin’s main function may be connecting the truck and trailer, but it has many additional advantages as well. Since 1991, kingpin has replaced other connectivity parts, majorly the ball joints, with simpler alternatives (kingpin) that can be serviced for less money in less time despite being more complicated. They are easier to automate and require fewer parts than one or two ball joints.

What Are The Different Types Of Fifth Wheels?

Two main types of fifth wheels perform the same function but vary slightly. The types of the fifth wheel are

A Sliding Fifth Wheel

As the name suggests, a sliding fifth wheel slides forward and backward. It can be used to carry a variety of weight loads depending on the cargo you are carrying. A sliding wheel attachment allows you to distribute the weight of the load you carry uniformly. Therefore, you can carry the varying amount of shipments.

A Fixed Fifth Wheel

This is fixed onto the semi-truck and cannot change its position. A fixed fifth wheel is best when transporting the same sized and weighted loads every time. As a result, it will not require any adjustment of weight.

Observe the requirements when selecting the type of fifth wheel to opt for. If you are a company that needs to carry varying amounts of the weight of every run, then having the sliding fifth wheel is the perfect solution. Whereas, if you need to tow the same load in an easy run, it’s best to go for a fixed fifth wheel.

Pros And Cons Of A Fifth Wheel



There are two main uses of a fifth wheel; to connect the semi-trailer to its truck component for even weight distribution and allow both components to move easily on every turn and uneven roads. There are both positive and negative aspects to a fifth wheel:

Advantages Of Fifth Wheel


There are many different types of RVs available for purchase. A Fifth wheel RV trailer can be connected to a truck using the fifth wheel whenever you are on the road again. It is also much cheaper, costing thirty to fifty thousand dollars, compared with a motor home, which costs more than a hundred thousand dollars.

The devaluation of a fifth-wheel trailer is also slow compared to a motorhome with many components that can fail and cause a large depreciation in the vehicle’s overall value. As a result, most people choose the more affordable option of the fifth-wheel RV.

Easy Turning

Flexible turning is one of the basic uses and advantages of a fifth wheel. An extremely large vehicle makes it difficult to perform even the smallest gestures on the roads, like changing lanes or taking turns. 

Therefore, having a fifth wheel frees up the front axles of the truck and allows for easy turning while ensuring that the trailer part of the vehicle follows. It is advantageous when using a fifth-wheel RV and driving on narrow paths, heavy roads, or parks. A fifth wheel is a great asset on a rough and bumpy ride as it does not disintegrate.

Lower Insurance

Another benefit of a fifth wheel is that as it costs less and does not include any heavy engine or its components, it does not require any substantial insurance. This means that the insurance cost of a fifth wheel is comparatively lower than an RV motorhome.

Less Gas

One of the additional benefits of having a fifth-wheel RV is that it uses significantly less gas when compared to a motorhome. This makes it a more affordable option as it provides all the important benefits like a motor home without requiring much in return.

Disadvantages Of Fifth Wheel

Difficult And Time Consuming

It takes time to get a fifth-wheel trailer ready. You will require one person to back the truck while another to guide him constantly. This can be a tedious task at every stop while traveling. Additionally, the fifth wheel requires stabilizing that tightens the connection, so it does not disconnect while driving. At the same time, a motorhome does not have such needs and is ready to go whenever you want.


It is also difficult to handle the fifth wheel on the road. In order to add the fifth wheel, you need practice and a clear idea of how to manage it during turning. Driving includes numerous maneuvers like turning and backing up, which will be quite different when you have a weight trailing behind you. Furthermore, attaching the trailer to the fifth wheel will require some assistance which may be difficult for solo campers.

Less Secure

While you are outside, there is always a chance of sudden attacks. Therefore, you may need to flee as soon as possible. With a motor home, it will be easy as you can simply drive away carrying all your belongings. But it is not the case in having a fifth-wheel RV, which must be attached first.


Is There A Specific Kingpin Size?

There are two kingpin sizes, and one is called the diameter, which is the smaller size and is used when less frequent loads are needed to be carried. In contrast, the other size is 3.5 inches which are used for hinging heavy weights and for more frequent uses.

What Is The Maximum Amount Of Weight A Fifth Wheel Can Carry?

A fifth wheel is utilized while hinging ranges of weights. The fifth wheel’s size and type will determine the load it can manage. However, it can carry loads ranging from 50,000 to 70,000 pounds.

Why Do You Need To Lubricate A Fifth Wheel?

A fifth wheel and a kingpin have parts that need to be connected; hence, sliding and attaching motion is involved. Therefore, it must be lubricated for smoother motion, reducing friction and decreasing wear and tear. The lubrication is especially necessary for winters when the weather is drying.


The fifth wheel has numerous advantages and has been a great part of it since its revolutionary invention. It can be used by contractors to carry weight or to connect trailers to make an RV. Two different types of fifth wheels can be selected depending on the use.

It may take some time to get used to driving a trailer with a fifth wheel attached, but it will be a better option than having a connected 18-wheeler. In order to maintain its original form, frequent lubrication is an important aspect that will increase its overall lifespan.


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