How do leaf springs work?

When truckers haul heavy cargo, drivers may notice unusual movements if the load weighs too much for the truck’s suspension. Correctly installed, leaf springs are a critical part of solving erratic trailer movements like swaying, for example. When a leaf spring is loaded it extends to force truck frames down, improving stability and handling on uneven ground. This extra weight helps absorb road shock, reduce brake wear and improve fuel efficiency by evenly distributing load weight. In this article, we explain what leaf springs are, how they work and their importance in the trucking industry.  

What are leaf springs? 

Leaf springs are stackable arc-shaped plates that act as a shock absorber for potholes and support vehicles’ braking systems. Located under the body of a vehicle, they’re designed to augment a vehicle’s standard suspension system. The leaf-shaped springs have been around for centuries, even appearing in Leonardo da Vinci’s early designs. Attached to a vehicle’s axle and chassis, leaf springs create a vertical connection that’s bendable on oddly shaped terrain. 

Why do commercial vehicles use leaf springs? 

Though leaf springs are most commonly found on buses, vans and trailers, they’re also used with many commercial vehicles. Along with air ride suspension, leaf springs are among the most common heavy-haul suspension systems on the market. When truckers need extra support for heavier loads, they can easily add extra leaf springs to their trailer suspension configuration. 

How do you install leaf springs? 

Leaf springs should be positioned behind the wheels, meaning wheels must be removed from the axle for correct installation. Once the wheels are removed, you should notice two small tabs called hangers on either side of the axle. These hangers can be used to properly position leaf springs in the brackets to attach to the wheel holes. After positioning the leaf springs, you attach the brackets to the underside of the frame with tools. 

Once your leaf springs are bolted to the hangers, they can be placed over or under the axle. These may be referred to as overslung and underslung, respectively. To cement your placement choice, use u-bolts to keep the springs flush with the axle. When fully secured, your leaf springs should be ready to go. 

If your trucking company has a mechanic, they should be able to knock this out for you in a couple of hours. If not, there are countless videos online of the installation process, or you can find a local mechanic for help.

Choosing the right type of leaf spring for your truck

Though there are a variety of leaf springs available, the leaf spring configuration you choose will depend on a number of factors. Considerations include your truck’s payload, carrying capacity, size, weight and type. Below we’ll go over the most popular types of leaf springs, how they work and what they’re commonly used for.

• Single-leaf — also known as monoleaf — is the most popular type for standard chassis configurations on light trucks or passenger cars. The single leaf’s attached to the front and back truck axles, with one main contact point along its length. It provides more area to add more weight without the frame bending or snapping. When used with standard chassis configurations, it doesn’t create much frame interference because it’s relatively narrow compared to other types.
• Multileaf or multiplier springs are most commonly used with long-haul trucks, including wheel towers and front ends for dump trucks. They add length and strength to the suspension system and help distribute weight evenly across the axles. Multileaf springs consist of multiple leaf springs of varying lengths that are stacked and staggered to keep heavier loads stabilized. The various leaf springs allow you to shift trucks’ centers of gravity.
• Twin leaf springs, also called dual leaf springs, are normally used for tractor-trailers. These springs can be attached to the front or rear of the truck to handle higher payloads. Their use enables more even weight distribution across the two axles without filling bed, cab or trailer space.
• Open-eye leaf springs are used for some of the heaviest materials because of their wide-angle connections. They can be bolted to the sides of an entire trailer frame to offer more stability than other types.

Leaf spring shapes

Leaf springs come in different shapes. These shapes vary based on your leaf spring configuration and type, which will already be determined by your need. Below we’ll list the most common leaf spring shapes.

• Semi-elliptical springs are normally used for multileaf springs, and have a curve like that of an undrawn bow.
• Elliptical springs are created using open-eye leaf springs. This configuration has two connected leaf springs that face away from each other, creating a semi-circle.
• Quarter elliptical springs, which are considered an older design, are used for a side heavy load.

Advantages of using leaf springs

You gain several advantages by using leaf springs:

• The systems are straightforward, low-cost suspension system additions for heavy hauls when installed aftermarket unlike coil and air bed systems.
• They’re easy to install and replace.
• Leaf springs are durable and have no maintenance costs for around the first seven years.

Disadvantages of using leaf springs

You’ll benefit from the many perks of a leaf spring system, but it comes with a few disadvantages.

• Leaf springs aren’t compatible with all trailer types.
• When dealing with deadhead miles, leaf spring suspension can cause a bumpier ride because there’s no weight to redistribute.
• Though they’re low maintenance, leaf springs are susceptible to the weather, which can cause corrosion and decarbonization.

“Leaf” it to the pros but don’t forget the cons

If you’re looking for an affordable way to expand your load capacity, look no further. Now that you know how leaf springs work, you can use them to help stabilize your trailer suspension. Just add a configuration that works for the types of loads you carry. This low-cost addition can make your life on the road more comfortable, safer and more profitable. Visit FreightWaves ratings for more truck maintenance tips. 

FAQ

Replacing leaf springs is just as easy as installing them. Just follow the original installation process in reverse, and then use the installation instructions for the new leaf springs. 

Leaf springs are better for heavy hauls, and they’re also more affordable. Coil springs work better for lighter loads if coils are already present and don’t have to be retrofitted onto a rig.

Heat causes leaf springs to decarbonize and become brittle, so you should never purposely expose them to them.

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