Why is it called a semi-truck? The real reason behind the name

Estimated reading time: 2 minutes 

How did trucks get the name “semi”? Weighing in at up to 80,000 pounds and typically 70-plus feet long, there certainly doesn’t seem to be anything “partial” or “incomplete” about the massive vehicles.  

If you’re wondering, “why is it called a semi-truck?” keep reading to find out how it got its name and what it really means.  

Why is it called a semi-truck?

 

Despite what you may think, the "semi" in “semi-truck” actually refers to the trailer, not the truck itself. In fact, the name “semi-truck” is just a shortened version of “semi-trailer truck.” 

This longer, lesser-used name more directly refers to the two parts that make up these large vehicles: 

• A towing engine (more commonly known as the tractor

  , or

  truck

  ), where the driver sits and controls the vehicle

  .

   

• One or more

  semi-trailers

  , which carry the freight.

   

What about all of the other names?

 

Why are 18-wheelers called semis, then? And why are tractor-trailers called semis? The answer is simply because “semi-truck,” or just “semi,” has become a catch-all term to describe the vehicles.  

The name “semi-truck” has been used since the early 1900s and remains the preferred term mainly because it's more convenient to say than the other, longer options.  

Though “semi” is the most popular, some other common terms include: 

• 18-wheeler.

  Mostly

  used in the South. 

• Tractor-trailer.

  Mostly used in the Northeast.

• Semi-truck-trailer.

• Big

  rig.

If you still find this a little confusing, you’re not alone. For example, what is the difference between a semi-truck and a semi-tractor, then? 

While both “semi-truck” and “semi-tractor” describe the towing engine portion of the vehicle, you can also use “semi-truck” to describe the entire vehicle, and others will understand what you mean.  

What is a semi-trailer?

 

Some of the key differences between a full trailer vs a semi-trailer are: 

Axle position 

• Semi-trailers only have rear axles,

  so

  half of the weight

  is supported by the back of the tractor

  .  

• F

  ull trailers have front and rear axles

  , s

  o they can fully support themselves.

Connection type 

• Semi-trailers

  connect to a tractor

  using a coupling mechanism known as a fifth wheel, which helps to distribute the load between the tractor and the trailer.

• Full trailers

  use a drawbar with a hook to attach to the tractor's hitch

  .

   

Capacity and use 

• Semi-trailers

  are

  generally 48

  to 5

  3 feet long.

  This, combined with

  the fact that only hal

  f

  of a semi-trailer's weight

  is

  supported by its own ax

  les,

  means they can transport heavier and larger loads. 

• Full trailers

  can range from 20 to 40 feet long.

  They

  generally carry

  lighter loads

  and are used for short-distance hauls, commonly to factories,

  ports

  and warehouses.

You’re more likely to see a semi-trailer than a full trailer on the highway, as it is the preferred method of long-haul transportation. Semi-trailers are preferred since they allow for: 

• A tighter turning radius.

• Easier backing ability.

• Trailers to be swapped/dropped off quicker and easier. 

That being said, if you’ve ever come across a tractor hauling multiple trailers (which requires a doubles and triples endorsement) the rear trailer is often a full trailer.