Semi Truck (18 Wheeler)

What is a Semi Truck?

A semi truck, in its most basic form, comprises two main parts: a semi tractor or towing engine and one or more semi-trailers to carry freight. The semi-trailer is “semi” because it doesn’t have the front axel and wheels and thus, must be coupled with the tractor unit. It’s this design that allows a single tractor unit to pull multiple trailers, increasing efficiency and reducing costs for transport businesses.
Semi truck is the most popular commercial motor vehicle (CMV) in the freight transportation industry.

These trucks are the backbone of freight transport in many countries, especially in the United States, where they transport over 70% of total domestic tonnage each year, according to the American Trucking Associations.

Anatomy of a Semi Truck

The key components include the engine, cab, transmission, chassis, wheels, and trailer.

Engine: Semi-truck engines are powerful. They are designed to pull heavy loads and are usually diesel-powered due to the fuel’s efficiency and torque advantages. Modern semi trucks can easily output between 400 to 600 horsepower, with some engines reaching even higher.
ET made a great video about the best diesel engines of all time.

Cab: This is the driver’s workspace and sometimes, living space during long hauls. It contains the steering wheel, controls, and gauges, and in the case of ‘sleeper’ cabs, also includes a bed, refrigerator, and other amenities.

Transmission: Semis use manual transmissions with far more gears than standard passenger vehicles, with some trucks having up to 18 gears. The high number of gears allows the truck to make the most efficient use of the engine’s power while hauling heavy loads.
Here is a very old and detailed video about semis transmission .

Chassis: Truck chassis is built to accommodate the heavy load of the semi-trailer and its freight. It includes the frame, axles, wheels, and air brakes.

Trailer: A semi-trailer is the cargo portion of the truck. It comes in various types depending on the goods being transported, including flatbeds, refrigerated trailers, tankers, and more.
Learn about the Types of Trailers used in the trucking industry here.

Size and Weight Of A Semi Truck

Let’s talk about how tall is a semi truck and how wide is a semi truck. The size of semi-trucks or tractor-trailers is regulated both at the federal and state level to ensure safety and infrastructure compatibility. Here are the typical dimensions for a semi-truck:

Length: The length of a semi-truck can vary significantly depending on the type of trailer attached. The tractor unit (the front part of the truck, which contains the engine and the cab) typically measures between 20 to 25 feet in length. The trailer length is more variable. The most common trailer length is 53 feet, but trailers can be as short as 28 feet in the case of “pup” trailers often used in pairs for less-than-truckload (LTL) shipping.

Width: The standard width for both the tractor and the trailer is 8.5 feet. This does not include the mirrors, which may extend the total width slightly.

Height: The maximum height for a semi-truck (including the trailer but not the cargo) is typically 13.5 feet to ensure it can safely clear bridges and overpasses.

Weight: The maximum weight is determined by the Gross Vehicle Weight Rating (GVWR), which includes the weight of the tractor, trailer, cargo, and anything else on board. Federal standards set the GVWR for a five-axle tractor-trailer at 80,000 pounds. However, weights can be higher in certain states under specific circumstances, or with special permits.

Keep in mind these are the general sizes for semi-trucks and there can be exceptions. For instance, specialized equipment, oversize loads, or different trailer configurations may require specific permits and have different legal size limits. Always consult the specific state’s Department of Transportation (DOT) for the most accurate and current information.

The Role of Semi Trucks in the Economy

Semi trucks are an integral part of the global economy, enabling the transport of nearly every product we use daily. In countries with vast geographical expanses, like the U.S. and Australia, semi trucks are particularly crucial in connecting remote areas with urban centers.

Furthermore, these trucks contribute significantly to employment, both directly and indirectly. From the manufacturing and maintenance of these vehicles to the drivers who operate them and the logistics managers who coordinate them, semi trucks are a sizable and vital part of the labor market.

The Future of Semi Trucks

As technology continues to evolve, so does the truck production. Electric semis are starting to make their way onto the roads, with companies like Tesla leading the charge. Their Semi model promises a range of 500 miles on a single charge, demonstrating that a future of environmentally-friendly freight transport is within reach.

Moreover, the development of autonomous driving technologies could revolutionize the industry by making long-haul transport safer and more efficient. However, the practical implementation of self-driving trucks on a large scale still faces significant technical, regulatory, and social hurdles.

In conclusion, semi trucks are the silent heroes of our modern world. From transporting fresh produce to our local grocery stores, to delivering critical medical supplies and everything in between, the wheels of these mammoth machines keep our world in motion.

Popular Makes & Models

Some of the most iconic semi trucks are Peterbilt 379, Freightliner Classic, Kenworth W900, Mack Super-Liner.
On the other hand some of the modern concepts today are Tesla Semi, Nikola One, Freightliner eCascadia, Daimler Freightliner Inspiration.
Learn about Power-Only Trucking here.
Learn more about Semi Trailers here.
Check out our Trucking Glossary here.
Learn about Maintenance here.

External Links

American Trucking Associations – Economics and Industry Data – click here.