What is a semi truck? In North America, the combination vehicles made up of a powered truck and one or more semi-trailers are known as “semis”, “semi-trailers”, “tractor-trailers”, “big rigs”, “semi-trucks”, “18-wheelers”, or “semi-tractor trailers” and “semi-trailer trucks”.


The tractor unit typically has two or three axles; those built for hauling heavy-duty commercial construction machinery may have as many as five, some often being lift axles.


The most common tractor-cab layout has a forward engine, one steering axle, and two drive axles. The fifth-wheel trailer coupling on most tractor trucks is movable fore and aft, to allow adjustment in the weight distribution over its rear axle(s).


Why Do They Call it a Semi-Truck?

A semi-trailer truck more commonly semi truck or simply “semi” is the combination of a tractor unit and one or more semi-trailers to carry freight. A semi-trailer attaches to the tractor with a fifth-wheel coupling as known as a hitch, with much of its weight borne by the tractor. The result is that both the tractor and semi-trailer will have a design distinctly different from that of a rigid truck and trailer.


What Are The Different Semi-Trucks Styles?

1. Flat Roof Sleeper

A sleeper cab or truck sleeper is a semi-truck that has a compartment attached to the cabin for the truck driver(s) to rest and sleep. Typically has a bunk and side storage compartments. The flat roof sleeper has a flat roof and less headspace.


2. Mid-Roof Sleeper

A 76-inch mid-roof sleeper is a semi-truck that has a compartment attached to the cabin for the truck driver(s) to rest and sleep. Typically has a bed, tv, and storage compartments. The mid-roof sleeper has a slightly higher and rounded roof for more headroom and space. 


3. Raised Roof Sleeper

A raiser-roof sleeper is a semi-tractor with a compartment attached to the cabin for the truck driver(s) to rest and sleep. Some sleeper offers a premium sound system, flat-screen tv, and side storage tower. The raised-roof sleeper has the highest roof for more space and better driver comfort. 


4. Day Cab

The day cab semi-trucks a tractor that is designed for day trips. It does not include the on-the-road overnight sleeping compartment. The purpose of the day cab is to hook up and haul large loads on short trips within the same day.


For more types and styles of commercial vehicles check out articles about the Different Types of Commercial Trucks & Vehicles


What’s The Difference Between a Semi Truck and 18 Wheeler?

Semi-truck refers to the actual truck or tractor, which contains the engine. Semi-trucks can run on its own without a hauling a semi-trailer.


18-wheeler refers to the combination of a semi-truck and semi-trailer. When connected they form a tractor-trailer unit, also referred to as an 18-wheeler. Which is based on the total number of wheels for the entire tractor-trailer unit.


What Is The Best Semi Truck?

Freightliner is the best selling semi-tractors in America today. They sales about 190K truck per year! Freightliner dominates with 40% of the commercial truck market share. They also employ over 3,000+ workers in their MT. Holly and Cleveland facility. 


Freightliner manufactures several models and styles of commercial trucks from on-highway, medium-duty, severe duty and natural gas vehicles. They are soon to roll out their new line of all-electric commercial vehicles named the Freightliner e-Mobility. There will be two models, the eCascadia and eM2 106.


To learn more about The Most Popular Semi Trucks in American read our latest article.


What Are The Different Types of Trailer for Semi Trucks?

There are several styles and types of commercial trailers for semi trucks. Here’s a list of the most common trailers in use today.


Flatbed Trailer

Lowboy Trailer

Reefer Trailer

Conestoga Trailer

Step Deck Trailer

Dry Van Trailer

Power Only Trailer

Extendable Double Drop Trailer

Stretch Double Drop Trailer

Stretch Single Drop Deck Trailer

Removable Gooseneck Trailer (RNG)

Stretch Removable Gooseneck Trailer (RNG)

Sidekit Trailers

Specialty Trailers

Multi-Car Trailer


For more details about commercial trailers read our article Different Types of Trailers for Semi Trucks.



Semi-trucks are a vital part of the USA economy and worldwide. Without semi-trailer trucks hauling freight, produce, and goods around the clock our economy would suffer. 18 wheelers are iconic. From trucking movies to songs about trucking driving, they’re part of Americana. Check out our article about the Top 100 Trucking Songs of All Time. What’s your favorite big rig? Comment below. Also, don’t forget to follow us on Facebook for more great trucking content.


About TopMark Funding®

We’re a truck financing and equipment financing company located in Roseville, CA. We specialize in commercial trucking and heavy equipment. With 20+ years of being in the commercial vehicle and equipment industry. Client satisfaction is our top priority at TopMark Funding®.


Our mission is to become your long-term financial partner by helping you grow your business and fleet. We’re not here for the short-term, we’re on long-haul with you. We achieve this by being your funding advisor, guiding you towards the best financial decisions for your trucking business.


If you’re in the market for a new or used 18 wheeler or a commercial vehicle we can help finance it for you. We have great rates, low down payments, and flexible monthly payments. We have lease and loan options for several different types of vehicles and trailers. Fill out the contact form or give us a call at (866) 627-6644. One of our finance specialists will contact you as soon as possible to go over your truck financing needs and learn more about you and your business goals.

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