All You Need to Know: A Beginner’s Guide to Semi-Trucks

All You Need to Know: A Beginner’s Guide to Semi-Trucks

According to the American Trucking Association, “3.5 million truck drivers [were] employed in 2018”, which is essentially no different from 2017. With this many truck drivers, we can infer that there are at least that many trucks out on the road at a given time. Semi-trucks play a key role in our ability to transport a variety of goods and materials nationwide. Without these machines, or their hard-working drivers, we wouldn’t have access to what we need.

As our need for certain imports increases, more trucks are needed to transport them to various locations across the United States. These complex machines are heavily relied on, so it’s crucial that every fleet owner and driver knows what’s within this guide to semi-trucks.

Basic Terminology

Before you purchase a semi-truck, you need to know the core terminology of what you’re looking for. Contrary to popular belief, the semi-truck itself only consists of the cab where the driver and engine are located. The long cargo hold, known as the semi-trailer, is a separate compartment that is latched to the truck prior to departing. This is what houses the goods and materials being transported. Once both pieces are connected, the truck as a whole is then referred to as an 18-wheeler, which is most often what people think of when they picture a semi-truck.

It’s also important to know the different terms for the size classes, as these indicate how much cargo the truck can hold and how much it weighs. Semis can typically fall into three different class sizes that you should be aware of—class 6, class 7, and class 8. Class 6 semis, for starters, generally weigh between 19,501 and 26,00 pounds and are most often used to transport beverages and lighter materials. Class 7 trucks, weighing between 26,000 and 33,000 pounds, make up the standard, as these have the widest range of potential cargo. If you need a trailer to handle cargo that’s a bit heavier, you’re going to want to go with a class 8. Weighing over 33,001 pounds, these trucks carry large quantities of very heavy materials.

Types of Semi Trucks and Trailers


Semis typically come in two distinct types, day cab models and sleeper models. Day cab semi-trucks are distinguished by their minimal design and are ideal for quick road trips to nearby locations. Smaller than other types of semis, the day cab has limited room for the driver and passenger so there is more room for the trailer it’s attached to. This makes a trip with a class 6 or class 7 trailer more efficient in the long run because it can carry more cargo in fewer trips.

Sleeper semis, on the other hand, are designed for longer trips. Unlike the barebones skeleton of the day cab, the sleeper semi often comes equipped with a small kitchen, bathroom, and bedroom for the driver to rest without the need to find a motel. These models, however, tend to be more expensive because of their amenities, and they typically carry less cargo due to the increased size. These models will most likely tote class 8 trailers, as the cargo they transport is more often heavier, even though there’s less of it.


The most common trailers seen on the open road include dry van and enclosed trailers. These are used to carry and protect cargo from harsh weather and unusual road conditions. Depending on what the cargo is, and how far it needs to be transported, these trailers could be the safer alternative to a flat bed.

Flatbed trailers are also a popular choice because of their versatility. They’re commonly used for construction materials but can carry everything needed for a project on its flat surface. Because it’s open to the elements, however, the driver has to take special care to tie the cargo down properly and tarp the materials to protect them.

Refrigerated trailers are similar to dry van trailers, but they’re heavily insulated and have a built-in cooling system to keep the transported goods fresh. Typically, the cargo in these trailers include frozen food or produce to be sold at a local grocery store.

Lastly, lowboy trailers take care of the objects that exceed the legal height limit that a truck can carry. Functioning as a flat bed, the lowboy trailer rests lower on its axels and is therefore closer to the road. This gives the driver more clearance when driving and helps them transport larger objects without worry.

Legal Restrictions

While you’re looking through different guides to semi-trucks, it’s crucial you pay specific attention to the legal restrictions of utilizing these trucks on the road. While some of these restrictions vary by state, United States federal law dictates that a semi is not allowed to exceed 80,000 pounds overall when traveling on the interstate highways, or 84,000 pounds on non-interstate highways. Breaking that number down, the semi-trailer with cargo should not exceed 34,000 pounds and the remainder of the truck shouldn’t be more than 46,000 pounds. These numbers can be increased or lessened based on the trailer’s contents, and several states offer exceptions to the rule if the semi is transporting specific goods.

As for its dimensions, it’s important to remember that semi-trucks can’t be any wider than 102 inches, longer than 48 feet, and higher than 16 feet for freeway roadways. These numbers can vary depending on the type of road it is and whether it’s in a rural or urban area. Be sure to research these requirements thoroughly before you leave on a trip to ensure that you’re within the guidelines.

What to Consider When Purchasing

Before you set out to buy a new semi for your fleet, it’s crucial that you make sure the one you’re looking at will serve your needs. Be sure to check the maintenance history of the vehicle to see if it has regularly broken down or has ever been severely damaged. This history could warn you about the issues a truck could potentially have and help you gage whether it would be worth the investment.

Other things to look for include loose seals on the windows or doors, cracks in the tire treads, corrosion on the brakes, broken lights or mirrors, severe rust, and leaking engine parts, as some of these could lead to a costly fix. Above all else, you need to ensure that the vehicle runs properly. It’s up to you to do enough research to make an informed decision about a purchase of this size.

If you find yourself interested in a truck that only needs mirror or light replacements, don’t let that be a deal breaker. Unitruck offers aftermarket parts for freightliner m2, volvo, and several other models to ensure that you get the most efficient vehicle possible.

beginners guide to semi trucks infographic