Sliding Tandems on Trailers: Meaning, Purpose, & Steps

The introduction of semi-trailers has revolutionized the trucking industry by transforming the ways that goods are transported. First introduced in the early 1900s, they have increased the efficiency and capacity of freight transportation as we know it today, with some trailers reaching up to 53 feet in length.

Unlike smaller trailers, longer trailers are often equipped with two axles in parallel, known as tandem axles, located in the rear segment of the trailer, working together to provide a single support system.

Sliding tandems is the process of moving one of the tandem axles along the length of the trailer to distribute the weight of the cargo more effectively. This ensures that the freight vehicle complies with weight regulations and maintains proper weight distribution for safe and efficient operation.

In this article, we’ll explain how sliding trailer tandems work and their importance when transporting cargo. We’ll also share a simple guide on how to slide tandem axles and also point out some valuable tips from experienced truckers. 

What Are Sliding Tandems?

Sliding trailer tandems is the process of moving one tandem’s axle position along the length of the trailer to set the optimal weight distribution when transporting cargo. By altering the axle placement forward or backward, drivers can change their vehicle’s load weight distribution and balance the downward force exerted by the cargo between the truck and trailer axles. 

Tandem axles are attached to a rail system under the trailer, enabling front and back sliding movement. Drivers can disengage the tandem axle’s locking mechanism and release them from their position using handles, levers, or a hydraulic switch that retracts the locking pin.

Once the pins are retracted, they can slide the position of the tandems accordingly to maximize stability and optimize the trailer’s weight distribution. Sliding the tandems forward (closer to the semi-truck) ensure that more weight is placed on the trailer’s axles.

On the other hand, sliding the tandem backward (further away from the semi-truck) places more weight on the truck’s axles. This sliding mechanism allows carriers to manage loads better and ensure compliance with regulatory bodies, particularly the Department of Transportation (DOT), at weigh station inspections.

It’s important to note that different jurisdictions have regulations regarding weight limits on truck axles to protect the roads from excessive wear and ensure road safety.

Why Truckers Slide Tandem Axles on Trailers

There are various reasons why carriers and owner-operators slide tandem axles when transporting cargo, ranging from achieving optimal weight distribution, adhering to state regulations, reducing wear on certain components, and more. Let’s explore some of these reasons in more detail.

• Optimizing Weight Distribution – Sliding tandems along a semi-trailer’s length is done to evenly distribute cargo weight across all axles – including the truck’s and trailer’s axles. Sliding forward shifts the cargo weight more to the trailer’s axles while sliding backward places more weight on the truck’s axles. Strategic tandem axle placement is crucial when transporting heavy cargo.

• Adhering to Regulations – The US Department of Transportation and other regulatory bodies mandate truckers to have no more than 20,000 lbs on a single axle and 34,000 lbs on tandem axles. Similarly, the UK allows a maximum weight of 9,500 kg on an axle with twin tires. Sliding tandems allow truckers to manage weight distribution accordingly and ensure compliance. 

• Optimizing Capacity – By shifting the position of tandems, truckers can increase their hauling capacity by distributing weight evenly across all axles instead of being limited by the maximum weight of a single axle. For instance, if an axle’s weight exceeds the legal limits, drivers can balance the distribution to prevent overloading and more cargo can be loaded without the consequential fines or penalties. 

• Reducing Wear and Tear – Even weight distribution can balance the downward forces applied on each axle that is caused by the weight of the trailer and its cargo. Too much stress on a single axle or its tires can accelerate its wear and tear, leading to preemptive repairs and more frequent maintenance. 

• Increasing Road Safety – A trailer and truck with a balanced weight distribution is safer to operate. Uneven distribution can increase the risk of rollovers, tipping, and other accidents. Moreover, it can make driving more difficult for truckers due to reduced control, especially during turns. 

• Lowering Fuel Consumption – The more stable a truck runs on a road, the less fuel it consumes. Sliding tandems help truckers find the optimal position for their axles when transporting cargo. The process also distributes friction and other forces evenly on the trailer, increasing the overall stability with improved braking, smooth acceleration, and proper gear shifting (for manual transmission trucks). All these benefits can prevent excessive fuel consumption and reduce the cost per mile. 

How to Slide Trailer Tandems

Below, you’ll find a step-by-step guide on how to slide trailer tandems when transporting heavy cargo. Ensure that you understand all of the sliding tandem parts before proceeding.

1. You’ll first need to check your gross vehicle weight rating (GVWR) to ensure compliance with federal and different state regulations. You must also check the permissible weight distribution in your jurisdiction before sliding tandems.
2. Ensure that your tractor unit is properly coupled and secured to your trailer unit as a safety precaution.
3. Next, you need to engage the trailer brake to keep it stationary and safe. You can engage it directly if your trailer has a dedicated braking system. Alternatively, you may also engage your trailer brakes from the tractor unit. 
4. Once the trailer is secure, locate the axle’s locking pins on the trailer railing and pull out or push in the lever/handle manually depending on the trailer’s axle unit build. Alternatively, if your tandems have a hydraulic mechanism, use a release switch to retract the pin. Doing so will allow the axles to move freely since the pin holding them in place would be disengaged from their connecting holes. 
5. The next step after you’ve released the pins is to slide the tandem axles along the trailer frame by moving forward or reversing the tractor. Do this very slowly to ensure that you only slide the tandems in small intervals.
6. Once the axle reaches the optimal position, apply the brakes and hold your position. You can ask someone to monitor your movement to simplify the process. 
7. Then, using the same mechanism for retracting the pin, engage the switch, pull, or push the lever to lock the pin back into the trailer’s connecting hole. If the pin is not able to lock into the hole as the tandems may not be aligned, repeat steps 4 and 5 until you have aligned the locking pin to the correct connecting hole before re-engaging the locking mechanism.
8. After successfully sliding the tandems, you must check the truck’s wheel alignment to ensure stability, safety, and weight distribution regulation compliance. 

Tips for Sliding Tandems on Your Trailer

Sliding tandems requires a proper mix of skills and experience. Below are some tips to help you improve every aspect of the process and accelerate the learning curve.

Carefully Inspect Your Surroundings

Before sliding your tandems, you should always inspect your trailer and the surrounding environment for any hazards or obstructions. Doing so will reduce the safety risks and ensure a smoother process.

Secondly, try to carry out this process in an open space so you have enough room to go forward or reverse with your tractor unit. Lastly, ensure the surface is leveled to prevent movement during the process.

Ensure The Trailer Brakes Are Engaged

As mentioned earlier, you must engage your trailer brakes to stop the tandem axles from sliding back and forth while you adjust them. Therefore, take your time to ensure the trailer wheels do not roll while you’re trying to slide your tandem axle. If you are unsure, there is no harm in double-checking your brakes or even disengaging and re-engaging them as an extra precaution. 

Double-Check Pins

Nothing is more important than safety when hauling cargo on heavy-duty vehicles. When it comes to sliding tandems, always double-check your pin and ensure it’s locked in place following the process. Tandem axles may continue sliding if they’re loose, which could damage the truck or cargo and even result in a major accident.

Control Your Speed

Speed control is crucial when sliding tandem axles and this process requires precision. Only use the accelerator if you’re operating a manual transmission tractor. If you’re driving an automatic transmission tractor, simply put it in gear and release the brake slowly.

Moving too fast could damage the pin or the locking mechanism. It could also loosen the pin and cause the trailer tires to slide over the surface excessively resulting in long-term wear on the components. With that in mind, take it slow and monitor the process closely. 

Check The Weight Distribution

The core purpose of equipping a trailer with movable tandem axles is to maximize hauling capacity and improve distribution. Therefore, you should always check the weight distribution before transporting cargo.

Sliding tandems along each hole interval on the trailer frame shift between 250-400 lbs to either the trailer’s or the truck’s axles, depending on the manufactured interval distance. We recommend visiting an independent weigh station to ensure your axles aren’t overweight.

While following this might not affect your ability to transport goods, it can prevent unnecessary fines or penalties if you miscalculate the distribution due to negligence or human error. 

Maintain Components Regularly

Regular maintenance is one of the most important aspects of operating a semi-truck and hauling cargo using different semi-trailers. Therefore, as a carrier or owner-operator, you must do your due diligence to ensure the brakes, sliding mechanism, and air lines are in optimal condition.

Doing so will ensure a smooth sliding process and prevent issues like rust, which can make it difficult to retract the pins. Proper maintenance can also prevent tandem axles from sliding uncontrollably, improving road safety. 

Adjust in Small Intervals

Finally, don’t rush the sliding process. Do it slowly in small intervals to prevent dragging your trailer wheels excessively, especially when shifting the axles toward the rear of the trailer.

Additionally, gradual adjustments along the trailer’s length allow you to easily find the optimal weight distribution point and prevent unnecessary wear and tear to the fifth wheel, tandem axles, and the trailer itself.