Exploring the Functionality of Lift Axles: Why HGVs Skirt the Ground

Have you ever noticed some trucks and trailers with wheels that don't touch the ground? This perplexing sight is actually due to the use of lift axles, which elevate or lower axles based on the vehicle's weight. This innovative feature helps in extending the life of truck tires and improving fuel efficiency. In this article, we’ll delve into the workings of lift axles, including their benefits and why they are essential for heavy goods vehicles (HGVs).

Why Do HGVs Have Lift Axles?

HGVs, particularly those carrying lighter loads, often feature lift axles to prevent unnecessary wear and tear. These axles can rise off the road surface, typically by using a load sensing valve that automatically descends when the load approaches the maximum permissible weight. Additionally, a switch in the cab can manually lower the axle. When a truck needs to carry more weight, the lift axle is lowered to the ground, providing additional axle weight and allowing the vehicle to carry more cargo.

The tag Axle: A Multi-Purpose Solution

The lift axles that don't touch the ground are known as tag axles. Named for their ability to be added as a tag or extra axle, these components can handle an extra 10,000 pounds of weight. They are typically found on 10-wheel dump trucks to manage potential overweight loads. Tag axles are essential in scenarios where the truck is fully loaded or loaded to the point where the axle weight would exceed the legal limit without them.

Imagine a scenario where a 10-wheel dump truck has a load that is just under the legal axle weight limit, but adding two extra wheels would spread the weight over a larger surface area. By lowering the tag axles, the truck’s total weight is reduced, thus remaining within legal limits. This not only avoids hefty fines for overloading but also protects the roads from undue strain caused by concentrated weight.

Benefits and Implications

Lift axles offer several advantages to HGV operators:

Reduced Wear and Tear: The axles that don’t touch the ground stay in better condition, extending the lifespan of the tires and other components. Improved Fuel Economy: With the axles in their retracted position, the truck's overall efficiency can be improved, resulting in better mileage. Legal Compliance: By lowering the tag axles when needed, the overall train weight can be avoided, keeping the vehicle within legal weight limits.

However, it's important to note that keeping the extra axles lowered can reduce fuel efficiency. This is because the extra weight of the axles being lowered introduces additional resistance during operation.

The reason behind the weight limits being determined by the number of rear axles is rooted in the principle of weight distribution. Each axle spreads the weight of the load over a larger area, reducing the risk of damage to the road. On a dirt road, a single axle would cause ruts, and on a paved road, concentrated weight can break up the pavement. By ensuring that the weight is distributed over multiple axles, the roads are better protected, and the overall wear on the infrastructure is significantly reduced.

Conclusion

Lift axles and tag axles are integral components of HGVs designed to optimize performance, reduce costs, and maintain road safety. The ability to raise and lower these axles based on the load not only extends the life of the vehicle's components but also minimizes the impact on the roads. Understanding how these systems work can help fleet managers and operators make informed decisions about their vehicle maintenance and usage.