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What are truck axles?


What are truck axles?

Wondering what truck axles are? You’ve come to the right place!

In this article, you’ll find a lot of information about axles, particularly those used for truck transportation.

What is an axle?

On a vehicle, an axle is a transverse shaft whose ends enter the wheel hub. Trucks have at least 2 axles.

These mechanical components are located at the front and rear of heavy trucks. Their purpose is to support the weight of the vehicle and maintain the space between the wheels.

Types of axles

There are different types of axles, all of which have distinct purposes and characteristics.

Load-carrying axles

You could say that all axles are load-carrying, because they support the weight of the wheels and the vehicle. However, this term is only used for axles that aren’t steering or drive axles.

Steering axles

Steering axles transmit steering commands from the driver to the wheels so that they turn and drive the truck in the desired direction. They are usually located at the front of the vehicle.

Drive axles

Drive axles transmit the power generated by the engine to the wheels. They are usually located at the rear of heavy transportation vehicles.

Axle groups

Any axle that is more than 2 m away from other axles on the vehicle is a single axle. Axles that are less than 2 m away from each other are considered an axle group.

Different types of axle groups have specific names.

Tandem axles

A tandem axle is a group of two axles that are less than 2 m apart. They are very common on heavy vehicles.

Tridem axles

A tridem axle is a group of three axles that are less than 2 m apart. These are more rare than tandem axles and are usually found on vehicles that carry very heavy loads.

Axle configurations on truck tractors

For a long time, the most common axle configuration for tractor semi-trailers has been a 6×4 drivetrain, where the rear tandem axle is composed of drive axles. However, some road transportation companies now have tractors with 6×2 configurations, where only one of the rear axles is a drive axle, and the other is just a load-carrying axle to help support the weight of the vehicle.

It should be noted that the two rear axles that form the tandem axle generally have 4 wheels each, two at each end.

Rigid axles vs. independent suspension

Rigid axles have been used to hold the wheels of vehicles since the invention of the automobile, and even earlier in the railway industry. Today, they are still found on all-terrain vehicles and heavy trucks because of their ability to support very heavy loads.

Independent suspension involves axles with one or two articulation points that allow the wheels to move independently of one another, which provides more control over the tilt of the vehicle in some circumstances.

Why learn about truck axles?

There are several reasons to learn about truck axles. First of all, in Quebec, the cost of registration for a truck, tractor-trailer or farm vehicle that weighs more than 3,000 kg is calculated according to the number of axles the vehicle and its trailer have.

Load limits are often calculated per axle as well, particularly during thaw periods. Therefore, heavy vehicles can add axles in order to temporarily increase their load limit.

How to count the axles

To find out how many axles a truck tractor or semi-trailer has, just look at it from the side. Count one axle for every single or double wheel you can see.

Don’t forget to count the steering axle at the front, the auxiliary lift axle and the attachable-detachable auxiliary axle.

Useful terms for distance and measurement

The distance between the front and rear axles of a vehicle is called the wheelbase. Track width is the distance between the wheels of an axle, measured from the centre of the tire’s contact with the ground.

Check out our blog for more useful information about the road transportation industry

This concludes our article on axles. We hope you found the information you were looking for!

If you’d like to learn more about the trucking industry and the transportation sector in general, feel free to check out the “news” section of There, you’ll find articles on subjects such as current events and regulations in effect.