As of 2025, there are 13 million trucks registered in the United States, and out of that number, TruckInfo states that 2.9 million are semi-trucks. In today’s article, we’re taking things back to basics and asking some common questions about those large vehicles that help transport much of what we see in stores. Rigs, semi-trucks, 18-wheelers—those are all terms used to describe large commercial trucks. With the economy being so dependent on trucks, have you ever wondered why big trucks have 18 wheels? Ever wondered why trucks have so many different names? We’ll be answering those questions and sharing other fun facts about 18-wheelers.
So why all the names? The name “semi-truck” has been used since the early 1900s and is still commonly used today throughout the United States. We start seeing variations or preferred terms depending on where in the United States you are. In the South, you will often hear “18-wheeler” or “big rig” used. If you are traveling in the Northeast, then you might hear them called tractor-trailers. And of course, there are also the terms semi-truck and semi-tractor.
Most semi-trucks have 18 wheels, but the number of wheels can vary from 10 to even 36 depending on the load these trucks carry. The federal gross vehicle weight limit is generally 80,000 pounds, which is why trucks require more wheels to help distribute the weight. The standard number of wheels you’ll usually see is 18, and there is a very specific way these wheels are placed on a truck.
- Two wheels on the very front axle, under the front of the tractor.
- Four wheels on the first rear axle of the tractor.
- Four wheels directly behind those on the second rear axle of the tractor.
- Four wheels farther back on the trailer, attached to one trailer axle.
- Four wheels at the rear of the trailer, attached to the second trailer axle.
As mentioned, the main reason semi-trucks have so many wheels and tires is to support the heavy loads inside a trailer. A load weighing thousands of pounds will put a considerable amount of pressure on the tires, and it’s simply not practical for a truck with only eight wheels to carry an 80,000-pound load. By distributing the weight across 18 or more wheels, the load is spread more evenly, ultimately placing less pressure on each individual tire.
Another thing to consider is braking because the force of braking will cause the cargo inside the trailer to shift. We experience this in smaller vehicles, but the force is much greater when the load is excessively heavy. With more wheels and tires, a truck can better handle the forces involved when this shift in weight takes place.
And now you know why semi-trucks are called 18-wheelers and why they need so many wheels. Trucks are such an integral part of our everyday lives, and nearly everything we buy has been transported by a semi-truck at some point. Despite that, they are still some of the most misunderstood vehicles on the road, even with more than one million truck drivers operating across the United States.
At Energie Fuel, we are proud to help trucking companies and commercial fleets save money on fuel while also understanding what it takes to keep their trucks on the road. Through our fuel card program, truck drivers can save money at the pump while traveling their routes, with access to thousands of fuel locations nationwide. Through our bulk lubricant and DEF services, fleet managers can also help maintain the health and performance of their fleet.