Road-tripping is one of my favorite things to do and I always wondered as I passed dozens of fifth wheels and semi trucks if it was possible to combine the two and have a semi truck pull a fifth wheel, so I did some research on it.
So, can you pull a fifth-wheel with a semi-truck? As long as the kingpin of the semi matches that of the fifth wheel it can work and be pulled just fine. Fifth wheels and semi trucks generally use a kingpin that is 2 inches in diameter. Even though it is possible, it is not generally recommended.
There are some other important things to know that specify what a semi-truck needs to be able to tow fifth wheels. Read on to learn more about kingpin size, checking the wiring, towing levels, and other important information that is critical for the towing process to work out fine.
The Kingpin and Towing Levels
Kingpins are basically parts of the fifth wheels and semi-trucks that help with coupling and pivoting of the vehicles. Kingpins are often the same dimension as fifth wheels, semi-trucks, and other commercial vehicles.
Both types of trailers often use kingpins that are 2 inches in diameter, however, sometimes semi trucks come with kingpins that are larger getting up to 3 1/2 inches in diameter.
As long as the kingpins match in size the semi can pull the fifth wheel without an issue. If they do not match, you will not be able to tow and will have to look into other options.
As mentioned previously, the grand majority of semi-trucks and fifth wheels use 2-inch kingpins this isn’t a common problem.
Semi-trucks were not technically designed to be pulling fifth wheels or other trailers like them, so it is also important to check the towing levels on the vehicles.
Making sure that the truck can tow the trailer level is very important. If the trailer is not towed as level as possible its nose can be too high or low. This causes instability and issues with swaying and other things.
It is very simple to check the towing level on the semi-truck and fifth wheel. You can do this in a few easy steps:
- Get the two vehicles on ground that is level.
- Measure the distance from the ground to the hitch on the semi-truck.
- Measure the distance from the ground to the pin pox of the fifth-wheel.
- Compare the measurements.
If they are the same or close the nose of your trailer won’t be too high or low. If there is a big difference you may encounter a height problem.
Check the Wiring
Semi-trucks weren’t initially made to pull Fifth Wheel trailers, so the wiring is a very important thing to check to make sure that both are connected together properly. Semi trucks typically have a 7-pin round socket, while Fifth Wheels only have a female RV 7-way blade style trailer connections.
Semi-trucks and other commercial trailers usually operate on a separate wiring system and fifth-wheel trailers use 2-wire systems with brake light and turn signal circuits that are combined.
Also, the majority of fifth-wheels have electric drum brakes which are wired to the 7-way connector as mention previously. Commercial trucks will typically have connectors for trailer lights with separate connections or brakes on the trailer. There are parts that can be bought to actuate electric trailer brakes called electric brake controllers which will wire into the 7-way socket for the fifth-wheel trailer.
An adapter may also be needed in order to connect a semi truck style connector to that of a RV connector.
Turn Clearance is Important
Once you have checked the kingpin size, wiring, level, and wiring of the semi truck and fifth wheel, it is crucial to also make the that the turn clearance is okay.
Could you imagine spending a good amount of time checking on all these other things to then go out driving only to have the semi and trailers collide into each other, or even into something else? That would be a huge bummer, which is why I have also spent some time researching just how to check that out to know how to make sure no problems like that occur.
There are two very important clearances to go over:
- Truck Cab to Trailer Overhang clearance
- Truck Frame/wheels to trailer clearance
In order to double check that there is enough cab to trailer overhang clearance, a measurement is needed from the center of the fifth-wheel hitch to the width of the trailer. As an example, if the trailer is 96 inches wide, the distance from the fifth wheel hitch to the semi’s cab must be 52 inches.
A simple equation can be used to figure this out in any situation:
Trailer width/Distance from fifth wheel to Semi cab + 4 inches = A good clearance.
To be able to find the truck frame/wheel to trailer clearance, a measurement from the center of the fifth-wheel hitch to the back corner of the frame/wheels will be required. Then, one will need to measure the kingpin on the trailer to the underside of the trailer.
The measurement on the trailer will need to be at least 5 inches greater than the measurement on the truck. If that is the case, then there is enough turning clearance room.
Semi-Truck Pulling Capacities
Semi-trucks are huge vehicles that are usually functional for about 200,000 miles and pull dozens of tons of weight. On average semis can pull around 40 tons! All this weight is usually spread out through up to 18 conventional wheels.
This comes out to be around 80,000 lbs. To put this into perspective a fifth wheel can weigh up to 1 ton, or about 2,000 lbs, but usually, they weigh much less. A truck like a Toyota Tundra on average can haul a load of about 5 tons or 10,000 pounds.
Is it Better to Pull a Fifth-Wheel with a Semi or a Truck?
There are many types of trucks with different makes and models that are designed and made to pull heavy cargo like trailers and fifth-wheels. Although semi trucks can potentially do that as well, it definitely isn’t as efficient or recommended.
The turn radius of a semi-truck often can make often make it very difficult to haul a fifth wheel around and is no easy task for anyone, especially for someone who isn’t experienced with driving vehicles that weigh thousands of pounds.
Trucks are much smaller, and although they can’t pull dozens of tons worth of cargo like a semi, the can pull the weight of a fifth wheel trailer without a problem.
Wiring complications are often a common issue for those trying to haul a fifth wheel trailer with a semi-truck. It can at times be hard to find the right adapters and hook the right wires in the correct places.
Trucks made by Ford, Chevy, Toyota, and other companies are often made for this specific purpose. This makes it extremely convenient, but easy to hook up the fifth wheel.
The convenience and easiness of pulling a fifth wheel with a truck far outweighs that of doing it with a semi, however, it isn’t wrong or impossible to do it the other way around if the situation arises.
What are the best trucks for pulling a fifth wheel? There are tons of great trucks that are built for hauling large cargo. Some, however, are better than others. In 2018 the top-ranked trucks for towing a fifth wheel include:
- Ford F-350 Super Duty
- Ram 3500
- Chevrolet Silverado
- GMC Sierra 3500
What is the average life span of a semi-truck? A semi-truck is usually designated to last for about 200,000 miles of use. The average semi truck engine will even run to up to 1,000,000 miles. These are trucks that are built to last for around 4-5 years
How much does a semi-truck cost? Semi-trucks can be pretty expensive. A new semi-truck usually costs anywhere from $80,000 to $150,000. There are also options to opt for a truck with lots of features and that could run up to $200,000.