Air vs Coil vs Leaf Spring Trailer Suspensions

Air vs Coil vs Leaf Spring Trailer Suspensions

28th Aug 2023

Suspensions plays a major part in ride comfort, this is especially true for caravans and trailers. Although there are many options available on the the market, the three main types of suspension systems used on trailers and caravans include: leaf springs, coil springs, and air springs. 

In this Cruisemasterclass, we'll take a closer look at each of these suspension types and explore their individual benefits and drawbacks.

Cruisemasterclass Episode 15: Air vs Coil vs Leaf Springs

Leaf Springs

Leaf springs are a more traditional suspension type that have been around for a long time. They consist of multiple leaves, constructed from spring steel that are held together in a pack and mounted to the vehicle frame at one end and to the axle on the other. 

One of the advantages of leaf springs is that they serve two functions. First, they support the weight of the vehicle, and second, they locate the axle. 

This means that there is no need for linkages to locate the axle relative to the rest of the vehicle, which is the case with other suspension designs such as independent or radius arms. 

Generally, leaf springs tend to deliver a poor ride quality, especially on trailers. This is because of something called interleaf friction, which is generated by how the leaves contact one another. Although this damping helps to reduce some of the motion of the suspension, it can be challenging for engineers to optimize this effect.

Additionally, leaf springs are typically over-sprung, with big leaf packs and rebound leaves, to make them strong enough to handle heavy off-road conditions. The stiffer and taller leaf springs often result in a stiff ride.

While leaf springs have been a proven trailer suspension option for many years, unfortunately the availability for locally produced leaf springs has greatly decreased. This has seen the general quality of leaf systems deteriorate. 

Coil Springs

Cruisemaster Coil Spring Suspension Illustration

Coil springs are commonly used on independent suspensions, which have become a popular alternative for trailers and caravans. They are simple, consisting of a spring along with a strut or shock absorber on the suspension arm, offering a consistent spring rate through the travel range. 

There are two main types of coil springs: linear springs and progressive springs. Linear springs have a fixed spring rate, meaning that the more weight that is put on them, the softer the ride will be. 

Progressive springs, on the other hand, can be tuned by varying the pitch (the gap between each coil) or by tapering the wire. Progressive springs are popular in off-road suspensions, where they provide a good balance between load carrying and ride comfort. 

Below is a short taken from the CruisemasterClass explaining the differences in spring types. 

Air Springs

Cruisemaster Air Spring Illustration

Air springs, also known as airbags, are another suspension type that is becoming increasingly popular. They consist of a rubber bag that is inflated with air to vary the spring rate. There are two main types of airbag suspension systems, these are convoluted bags and rolling sleeve bags. Convolute bags generally have two convolutes, however some systems use three convolutes for longer travel applications. 

While rolling sleeve bags are more commonly used in industrial applications or as a helper spring on the back of a Ute. Additionally, rolling sleeve bags offer plenty of tunability, making them versatile to handle different loads and road conditions.

Both air bag systems perform the same function by varying their spring rate through air pressure delivered from a compressor, offering a good ride quality, absorbing shock and vibration well.

For more caravan and towing tips, make sure to keep an eye out for the latest episodes of our Cruisemasterclass series by subscribing to the Cruisemaster YouTube channel and following us on Facebook & Instagram.

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