What is the suspension on a trailer?
You know your car or truck has suspension, but what about the trailer you’re towing behind it? Understanding the trailer’s suspension system is absolutely crucial for safe towing and protecting your cargo, but it’s a topic that is often overlooked.
The suspension on a trailer is the system that connects the axle and wheels to the trailer’s frame. Its main job is to absorb shocks from the road, which provides a smoother ride for the cargo, reduces stress on the trailer’s frame, and keeps the trailer stable and controllable at highway speeds. The two most common types are leaf spring suspension and torsion axle suspension.
As a supplier of suspension parts for nearly everything with wheels, I can tell you that a trailer’s suspension is just as important as the one on your tow vehicle. A failure here can be just as dangerous as a failure on your car. The type of suspension a trailer has determines how it rides, how much weight it can carry, and how it needs to be maintained. Let’s look at some of the most common questions people have about these hardworking systems.
How to tell if trailer suspension is bad?
Your trailer seems to be bouncing more than it used to, or maybe you’ve noticed that the tires are wearing out strangely fast1. Ignoring these signs can lead to an unsafe towing situation2, costly damage to your tires, and even damage to the trailer’s frame or your cargo.
You can tell a trailer suspension is bad by looking for physical damage like cracked or broken leaf springs, worn-out rubber bushings, or a frame that is sagging to one side. Other clear signs include excessive bouncing after hitting a bump, strange noises like clunks or squeaks, and uneven or rapid tire wear.
A quick pre-trip inspection can save you from a major headache or a dangerous situation on the road. Here is a simple checklist you can use.
Visual Inspection Checklist
- For Leaf Springs: Look closely at the stacks of spring leaves. Are any of them visibly cracked, broken, or have they shifted out of alignment? Check the U-bolts that hold the axle firmly to the springs; they must be tight. Inspect the small rubber bushings in the "eyes" of the springs and the shackles; they should not be cracked, bulging, or worn into an oblong shape.
- For Torsion Axles: This is a bit trickier. Look at the angle of the torsion arm where the wheel is mounted. When the trailer is empty, this arm should be angled slightly downwards. If it’s parallel to the ground or pointing up, the internal rubber cords have likely failed. Also, look for any stress cracks in the trailer frame around where the axle is mounted.
Performance-Based Clues
- Tire Wear: Uneven tire wear is a huge red flag that something is wrong. It tells you the axle is no longer being held in the correct position by the suspension.
- The Bounce Test: If you push down hard on a corner of the empty trailer, it should return to its position and settle quickly. If it bounces up and down multiple times, the suspension system has lost its ability to dampen motion.
What is a strut on a trailer?
You are familiar with struts on a car, but do trailers use them too? The terminology in the parts world can be confusing, especially when you are looking for components for less common types of trailers or equipment.
It is extremely rare for any standard trailer to use a strut. The term "strut" refers to a specific type of suspension damper that is also a structural, load-bearing part of the suspension, which is common on cars. Trailers almost exclusively use either a leaf spring system or a torsion axle system, neither of which incorporates struts.
Let’s clarify the difference.
Why Trailers Don’t Use Struts
A MacPherson strut, the type found on the front of most passenger cars, is a complex, load-bearing component that often integrates the shock absorber, the spring, and the steering pivot into one single unit. Trailers don’t have a steering system for their main wheels, and their suspension needs to be as simple, robust, and cost-effective as possible while being able to handle very heavy loads. Leaf spring systems and torsion axle systems achieve this goal much more effectively.
The Exception: Shock Absorbers
Now, while trailers do not use struts, some higher-end or heavy-duty trailers do use separate shock absorbers. These are often added as an upgrade to a leaf spring suspension to provide better damping and control the bouncing motion of the trailer. This is a very common and highly effective upgrade that dramatically improves how a trailer tows. So, if you see a part that looks like a shock absorber on a trailer, that’s exactly what it is—a shock absorber, not a strut. As a parts warehouse, we stock these trailer-specific shock absorbers, which are valved differently than car shocks to handle the unique loads and motions of a trailer. It’s very important to know the difference to get the right part for the job.
What is the strongest part of a trailer?
When you’re loading up your trailer with heavy equipment, building materials, or other valuable cargo, you want to be completely confident in its strength. Understanding the backbone of the trailer’s structure helps you use it safely and avoid the dangers of overloading.
The strongest part of any trailer is its frame, specifically the main longitudinal frame rails and the tongue that connects to the tow vehicle. These components make up the foundation upon which everything else is built. The axle assembly is also a critical strong point, as it’s the component designed to carry the entire weight of the trailer and its cargo.
Let’s look at these two key structural areas.
The Foundation: The Frame
The frame is the trailer’s skeleton. It’s typically made from welded C-channel or box-tube steel. The two main rails that run the length of the trailer, along with the various crossmembers that connect them, are designed to bear the distributed load of the cargo and resist the immense twisting and flexing forces that occur during towing. The tongue is also massively reinforced because it has to handle all the pulling, stopping, and turning forces from the tow vehicle.
The Weight-Bearer: The Axle
While the frame provides the overall structure, the axle is the component that truly carries the load. Trailer axles are thick, heavy-walled steel tubes that are precisely engineered to support thousands of pounds of weight. When we talk about a trailer’s capacity (for example, a "3,500 lb axle" or a "7,000 lb axle"), we are referring to the certified load-bearing strength of this specific component. The suspension’s job is simply to attach this very strong axle to the very strong frame in a way that allows for controlled movement.
What is a gorilla lift on a trailer?
You’ve probably heard the term "Gorilla Lift" in relation to utility trailers, but you might not be sure what it is. Is it part of the suspension? Does it increase the trailer’s weight capacity? Understanding these common accessories is key to knowing a trailer’s features.
A Gorilla-Lift™ is not part of the trailer’s actual suspension system. It is a popular brand name for a lift-assist system designed for the heavy rear ramp or tailgate of a utility trailer. It uses a system of springs and rollers to make the tailgate feel nearly weightless, which makes it much easier and safer for one person to lift and lower.
Let’s clear up what this device is and what it isn’t.
A Helper, Not a Suspension Part
It’s a common point of confusion, but a Gorilla-Lift has nothing to do with the axles, the springs, or how the trailer rides down the road. Its entire purpose is to counteract the weight of the tailgate itself. Heavy-duty utility trailers can have steel-mesh or solid steel tailgates that weigh 100 pounds or even more. Trying to lift this dead weight can cause serious back injuries. The Gorilla-Lift system attaches to the trailer’s side rails and to the tailgate, and its clever spring mechanism does all the heavy lifting for you.
Why the Confusion?
I believe the confusion comes from the word "lift." In the automotive world, the word "lift" is almost always associated with suspension lift kits that raise the height of a truck or SUV. In this case, "lift" simply refers to the physical act of lifting the tailgate. As a suspension parts warehouse, we don’t carry this type of accessory, but it’s very important for us to know what it is so we can correctly answer customer questions when they call us. It shows our expertise extends to the entire trailer system, not just the specific parts we sell.
Conclusion
A trailer’s suspension, whether it’s a simple and durable leaf spring system or a smooth-riding torsion axle, is a critical component for safe towing. Knowing how to spot the signs of wear and understanding what each component does ensures that your trailer, and your valuable cargo, will arrive safely at your destination.
GSW to safeguard your needs.
