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Trailer Suspension & Axles

When it comes to your trailer’s axles or suspension, you often choose to replace old or worn trailer parts with similar parts. Sometimes, however, it’s a better option to replace the axle or suspension to accommodate the trailer’s use. Trailer axles and suspension systems need to be hard-wearing and reliable, and to get the best performance out of your trailer, you should make sure that the axles and especially the suspension are suitable for trailer use.

Trailer Suspension

Leaf Springs

The steel leaf spring is one of the oldest forms of suspension, first patented by British inventor Obadiah Elliott in 1804. Of course, things have changed a bit compared to the traditional leaf spring, but the principle is still there.

Trailer Suspension

So, you might think this 200-year-old invention is a little dated for use on your shiny new trailer. But there’s a good reason they’re still one of the most popular trailer suspension systems you’ll see today – they’re exactly the kind of trailer suspension you want! They are one of the least expensive types of suspension, easy to maintain/repair/replace, durable, and can carry very heavy loads while distributing the stresses and strains that can damage a trailer or axle.
The best thing about leaf springs is their adaptability to almost any trailer weight. From a single leaf spring used in light trailers to 12+ leaf springs used in larger trailers. No matter how big or small the springs are, they all work in the same simple way. The only thing that matters is matching the right leaf spring to the right trailer application. Springs with lower load ratings will bottom out and eventually fail, and springs that are too heavy and stiff will not dampen any bumps or vibrations.
Steel leaf springs are designed to slide against each other as they are used, so they will inevitably eventually wear out and need to be replaced. This means that the material and finish of your leaf spring will affect how long it lasts. Painted or galvanized springs are the most popular choices, with painted springs being the longest lasting of the two. Sometimes the heating and manufacturing process used to make galvanized steel springs can make them slightly weaker and lose flex faster than painted springs.

Slipper Leaf Springs

The slipper leaf spring is one of the simplest forms of leaf springs. As the name implies, this spring has a sliding element called the spring tail. This area of the slipper leaf spring is particularly prone to wear when rubbing against slippers. Traditional slipper plate springs are also known for being noisy on rough terrain. There are non-slip versions of slipper plate springs available to solve this problem.

Trailer Suspension

Sliding leaf springs provide excellent lateral stability, making them ideal for trailers with two or more axles. These springs are also very compact, making them ideal for trailers with low deck heights when connected to a single axle.

Double Eye Leaf Springs

Compared to a trailer leaf spring, a double-hole leaf spring adds additional loading points to the chassis. The three loading points on a double-hole leaf spring help to further distribute the stress and load on the trailer to minimize the stresses placed on the chassis and axles. This type of spring needs to be installed and set up correctly to take full advantage of its benefits – incorrectly installed springs can seize when the trailer is driven over extremely bumpy terrain or overloaded.

Trailer Suspension

These springs are well suited for single-axle trailers, but they lack the lateral stability of the sliding leaf springs used in multi-axle setups. Their added complexity makes them slightly oversized, which limits the height of the trailer deck.

Parabolic Springs

A parabolic spring is a modern form of leaf spring that usually consists of just one piece of leaf spring that is thicker in the center and then tapers toward the ends. This spring is designed to eliminate the friction between the leaves that causes other types of leaf springs to wear. This type of spring is usually lighter than a standard leaf spring and has a smoother ride due to the reduced stiffness. This reduction in stiffness results in a lower maximum load capacity of the spring. This can be combined with multi-layer parabolic springs that are designed with a spacer between each leaf – which of course also puts extra weight on the spring.

Trailer Suspension

Despite the single-leaf design, parabolic springs can take up a lot of space underneath the trailer, thus limiting the minimum deck height – a situation that can be exacerbated if a multi-layer spring setup is used.

Torsion Suspension

Torsion suspensions are preferred for boat trailers because they are less prone to rust damage. They consist of a rocker-type axle, called a torque arm, that rotates inside a rubber housing. The suspension system converts the oscillating motion of the axle into a rotating motion by the torsion arm, which is then dissipated by the rubber inside the housing. The elasticity of the rubber returns the swing arm to its original position.
This type of suspension provides a very smooth ride because it is completely independent of each wheel of the trailer. The low profile of the torsion unit means that the deck height of the trailer is very low. One of the main limiting factors of the torsion suspension is its relatively limited load capacity, which is around 2500kg maximum on a tandem trailer.

Trailer Suspension

The lack of axle sharing also means a significant increase in stress on the trailer chassis. This can be so dramatic compared to other types of trailer suspensions that it can reduce the load carrying capacity of the chassis by up to 25%.

To Summarise

The axles and suspension you use on your trailer may have a much greater impact on the use of your trailer than you think. That’s why it’s important to match the suspension and axle setup to the trailer’s intended use as closely as possible.
The suspension usually determines the type of axle you can use, and the number of axles the trailer needs to achieve its purpose. If you need any help or advice on installing the correct axles and suspension for your trailer, please contact us at TrailerTek.

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