what is leaf spring?
Leaf springs are a basic form of suspension made up of different-sized layers of steel sandwiched on top of each other.
Most leaf spring assemblies are formed into an elliptical shape through the use of spring steel, which has properties that allow it to flex when pressure is applied to either end but then return to its original position through a damping process.
The steel is generally cut into rectangular sections and then held together once by metal staples at either end or a large bolt through the center of the sheets. It is then mounted to the vehicle axle using large U-bolts, securing the suspension in place.
What does a Leaf Spring Do?
Leaf springs are an integral part of your vehicle’s suspension system. They are installed to help support the entire weight of your car or truck. Leaf springs also help to maintain the tire’s grip on the road and regulate the wheelbase lengths when it is speeding up or slowing down.
Due to their advantages, leaf springs are in great demand. Occasional transportation is just one-way leaf springs have contributed to our transportation industry. Nowadays, leaf springs are more popular on heavy-duty vehicles like trucks, SUVs, and vans.
How Do Leaf Springs Work?
If the load weight or a vehicle is too high, a lot can happen. Your vehicle/trailer may start bouncing more or swaying from side to side. If this is the case and the vehicle being towed is too heavy, there may be a problem with the suspension.
If the suspension is too rigid, the wheels will sometimes leave the pavement when hitting bumps in the road. Soft suspension can cause the truck to bounce or sway.
However, good suspension ensures that the wheels stay on the ground as much as possible. Leaf springs are a great way to keep towed loads stable and ensure the load stays on the ground.
Parts of leaf spring
- Add-A-Leaf’s. An Add-A-Leaf is an extra leaf added to a leaf spring pack. Added leaves are installed to increase vehicle carrying capacity or to reduce sway by creating a firmer ride. They can also be used to increase the ride height of your vehicle.
- Centre Pins. Effectively, the center bolt holds the leaves together and puts them in contact with the axle. The center bolt head connects to the axle, which gives the truck its rear suspension in combination with the leaf springs.
- Degree Shims. Steel shims to go between your leaf springs and your spring perch. These are used on leaf spring vehicles in order to adjust pinion angles and achieve proper driveline geometry.
- Fitted Leaf’s. Fitted Leafs are designed as an option Exclusively for Skyjacker(R), Soft ride(R), and Lifted Leaf Springs. These are used when the additional weight of aftermarket accessories is installed such as a heavy winch bumper, swing tire carrier, or all your extra gear.
- Shackles. A shackle is an integral component of the suspension system that attaches between the leaf spring and the vehicle frame. It allows for the leaf spring to work through length changes during suspension articulation.
- Spring Eyebolt Kits. It’s a grade 10.9 hardened steel bolt that typically fits many standard truck and van springs.
- Spring Perches/Mounts. Leaf Spring Perches are welded on top or below your axle tube. Your leaf springs rest on top of the spring perch. Stock perches can collapse or get bent out of shape over time and need to be replaced.
Types of Leaf Springs
#1. Elliptical Leaf Springs.
Elliptical leaf springs come in quarter, half, three-quarters, and full shapes. Semi-elliptical springs are most commonly used on trucks. These springs are parabolic in shape and appear on both the rear and front axles of trucks and only on the rear axle of cars.
Older subcompact models used the less efficient quarter-elliptical leaf springs. These looked like half a semi-elliptical spring. By combining this type of elliptical nib with a semi-elliptical nib, manufacturers created three-quarter nibs. However, these fell out of favor like quarter springs and only appear on older cars today.
Some manufacturers thought that if semi-elliptical leaf springs worked well, it would be better to place two of them facing each other in full elliptical spring. However, this design option failed because the pressure of the spring affected the alignment.
#2. Transverse Leaf Spring.
Transverse leaf springs have the same shape as semi-elliptical models. However, these springs will fit under a truck with the base of the curve pointing toward the chassis and not toward the ground.
In addition to their change in orientation, these leaf springs also have a different location than their semi-elliptical counterparts.
This upside-down installation takes place on the sides of the vehicle instead of on the front or rear axle. Lateral leaf springs are rarely seen on trucks or other vehicles these days.
#3. Platform Leaf Spring.
Platform leaf springs use a pair of semi-elliptical leaf springs – one pointing down and the other pointing up. When attached to the vehicle, the springs support three points of vehicle weight along each side.
Multi-Leaf Springs
It doesn’t take a genius to figure out that the name comes from the fact that the spring is made up of more than one metal plate. The panels are placed on top of each other and joined together, making it easier for vehicles to carry heavier loads with less strain.
With a multi-leaf spring, the size of the plates gets smaller as you look down. The panels are laid lengthwise to layer them, the longest piece being made with grommets or hooks at the top to hold the feathers in place.
Multi-leaf springs are considered to be the most common type of leaf springs for light commercial vehicles and heavy commercial vehicles. The stacked format means the feathers are thicker in the center, which is known as the semi-elliptical look.
Mono Leaf Springs
Mono leaf springs are better suited for LCVs than trucks as they are not designed for heavier vehicles. They are thicker in the middle and gradually thinner towards the ends, similar in structure to the multi-leaf system but without the extra plates.
The single leaf spring system used to be popular, but when it started to break on heavier vehicles, it went somewhat out of style. They can still be seen and used, but not when the vehicle in question requires protection against a heavy load or the weight of the vehicle itself.
Leaf Spring Capacity
Just as there are different types of leaf spring shapes, there are also different capacities in terms of the number of leaves and leaf spring sizes. Check leaf spring capacity specifications.
Another essential aspect when selecting leaf springs is knowing the capacity required. Exceeding this load capacity on a regular basis can cause excessive wear and premature failure of your leaf springs.
Consult your truck’s owner’s manual to determine storage capacity. If this amount is too low for your typical shipping weights, consider upgrading the rear leaf springs to provide more support for the rear of your truck.
Find springs that offer more weight capacity than your vehicle is currently using. In order to select the correct springs, you may need to upgrade from your truck’s stock springs to heavy-duty leaf springs.
Uses Of Leaf Spring
The application of the leaf spring is the damping of shocks and vibrations in mostly heavy commercial vehicles such as trucks, vans, buses, railway wagons, etc.
Leaf springs are still used today in heavy commercial vehicles such as vans and trucks, SUVs, and railroad cars. On heavy vehicles, they have the advantage of distributing the load more widely across the vehicle chassis, while coil springs transfer it to a single point.
Leaf Spring Advantages
There are quite a few significant advantages of the leaf spring. We have listed a few of the key advantages below:
- The way the suspension is constructed is really simple and strong, acting as a linkage that holds the axle in position without the need for a separate linkage.
- Extra weight and costs are reduced because of the rear axle location. This eliminates the need for trailing arms and a Panhard rod (AKA track bar).
- Leaf springs support the weight of the chassis, making them ideal for commercial vehicles.
- They also control axle damping.
- The chassis roll can be controlled more efficiently due to the high rear moment centre and wide spring base. If the springs are mounted wider apart, the roll tendencies will be less.
Leaf Spring Disadvantages
Although there are many key advantages of the modern-day leaf spring (especially when installed in commercial vehicles), there are also a couple of disadvantages which you should be aware of. We have listed these below:
- Wind-up and vibration can be caused by acceleration and braking torque. The wind-up can also cause nose-diving and rear-end squats.
- They aren’t always the easiest to install – but there is a clear process to follow that makes life much easier.
- The ride comfort isn’t as great because of the inter-leaf friction between each leaf.
- Over time, the springs tend to lose shape and can sag. When the sag is uneven, it can alter the cross weight of the vehicle which can affect the handling slightly. This can also change the axle-to-mount angle.
- Wind-up and vibration can be caused by acceleration and braking torque. The wind-up can also cause nose-diving and rear-end squats.