As the technology on diesel engines became more advanced, dump trucks were able to carry bigger, heavier loads. Compared to earlier versions, these modern vehicles generate more horse power and torque per liter of engine displacement then they ever did years ago. Unfortunately, truckers were unable to maximize the power of their equipment due to the axle weight limit restrictions set forth by the Department of Transportation. Thankfully, there is now a way to get around this problem with the help of movable axles.

The regulations set forth by the Department of Transportation regarding load capacity were created to extend the service life of public roads. Carrying tons of moving weight can add a great deal of stress to roads, reducing the length of time until repairs or replacement are needed. To avoid this problem, the Department of Transportation has set a maximum weight capacity per truck axle.

What is a Movable Axle

A movable axle is an additional set of wheels located behind the dump truck bed. The wheels have their own chassis that connects to the main chassis via an articulated joint. Two hydraulic rams also connect this movable part and the main body to retract or deploy it into position. Unlike the standard tandem differential, this movable shaft is not powered although it does have brakes.

Importance of a Movable Axle

Due to the fact that the Department of Transportation's method of measuring a truck’s weight is per axle, adding an extra trailing one on the vehicle increases its load capacity without going beyond the set legal weight limit. Adding another set of wheels that is in contact with the road effectively divides the weight of the entire load to each one.

When the movable rod is deployed, the overall length of the equipment also increases by 11 to 13 feet. Having this extra length also raises the legal weight capacity of the vehicle under the federal bridge formula. Having a longer wheel base effectively distributes the weight of the vehicle over a longer distance, thus reducing the amount of weight applied to the road surface.

Special Considerations

Having a trailing axle ready to increase capacity is a handy feature, but there are a few important things that operators must consider. Having an extra set of wheels behind the chassis increases the overall length of the truck and also increases its turning radius and overall mobility. The longer the vehicle, the more side space it will require for a turn. The difference in the mobility of this vehicle is evident when driving through traffic and tight streets. The extra set of wheels also creates additional drag and increases engine workload.

To avoid these problems, drivers are advised to only use the movable axle whenever absolutely necessary. If the weight of the load being carried is well within the capacity of the regular tandem used on a dump truck, then the movable rod should be retracted. Doing so will increase the tread life of the wheels and reduce engine workload.

The development of the movable axle has made these vehicles more adaptable to various operating conditions. It gives operators the flexibility to carry heavier loads without going beyond the government’s regulations. Finally, the dump truck can be rescued from weight restrictions with help from movable axles!