Semis Have 10 Wheels, So Why Are They Called 18-Wheelers?

Why is a semi called an 18-wheeler when it only has 10 wheels? There are reasons why semis have 10 wheels, but a large portion of this misconception boils down to a matter of semantics—how you define a wheel versus a tire.

Here’s a quick explanation to set the record straight.

What is a semi truck and trailer?

A semi is a tractor (which houses the engine and cab) and a trailer. They’re often used to transport cargo over land. Typically, the tractor has two to three axles with up to 10 wheels, while heavy-duty tractors may have up to five. The most common layout is one steering axle and two drive axles, along with a forward engine. Axles help distribute the weight load throughout the entire tractor and trailer.

Semitrailers attach to the tractor by means of a hitch. The trailers usually have two axles, which may have four tires each. That’s why people think of semi trucks and trailers as 18-wheelers.

The difference between wheels and tires

The term wheel can refer to rims, hubs or tires. Each wheel rim has a tire attached, just like the tires on your regular vehicle. Hubs, on the other hand, are the structures to which rims are attached by studs. The hub rotates with the rim. Finally, tires are self-explanatory—they’re the cushioned rubber parts of a vehicle’s wheel, which support the vehicle and grip the road.

The confusion starts when people are not clear on what they mean when they use the word wheel. Eighteen-wheelers have 18 tires but not hubs.

A generic term

Based on the explanations above, you might be wondering what semi trucks with more than five axles or 18 tires are called. The answer is a semi truck or an 18-wheeler. Even though some semi trucks have more than 18 wheels, this has become a generic term, like Kleenex or Band-Aid.

Therefore, it’s not really necessary to count the axles and tires on every semi truck before you call it an 18-wheeler—truckers and everyone else will know what you mean. By the time you realize that some trucks eschew double tires on each side for large single tires, you will understand why it’s easier to just use a generic term.

Truck service and repair

Now that you know why a semi might be called an 18-wheeler, you can focus on the more important stuff: Who will repair your 18-wheeler if something goes wrong? Complete Truck Service, Inc. offers truck and trailer repairs and service. We have nearly 40 years of experience in everything you need to keep your semi running smoothly, including 24/7 jump starts, roadside assistance towing and more.

When you own or operate semi trucks for a living, it’s important to know which mechanics you can trust. Complete Truck Service, Inc. is here to help you any time of day or night, for any repair you may need. Reach out to us today, and keep our number on speed dial in the future.

Categorised in: Truck Service

This post was written by Writer