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-quarter, 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.
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.
What are the advantages?
Due to the sheer amount of metal layers, leaf springs provide a large amount of support between the car’s wheels, axles, and chassis. They can absorb enormous vertical loads due to their close-meshed structure, which is why they are still used in the heavy-duty industry.
Vertical loading is also distributed along the length of the leaf spring rather than acutely through a small spring and damper, potentially creating a concentrated force too large for the suspension.
In a car, damping can be an extremely important property. If the suspension is under-damped, the car will roll and bounce around well after hitting a bump or pothole in the road.
This was a significant feature on cars that used coil springs before the shock absorber appeared, and was detrimental to cars when driven at real speed. Leaf springs coped much better with car damping due to the friction between the individual steel plates, which made the reaction time after a vertical flex in the suspension much quicker, resulting in a much more controllable car.
What are the disadvantages?
A major downside to leaf setups is that they aren’t brilliant when it comes to suspension tuning. In racing and performance car applications it is important to be able to manipulate a suspension setup for driving conditions and for different driving styles, which is much easier these days with adjustable coil overs.
This lack of adjustability in blade assemblies is accentuated by the fact that the ends of the leaf springs are attached to the chassis, leaving very little room for shortening or lengthening of the blades.
Adjustments can therefore only be made through the strength and flexibility of the material from which the leaf springs are made.
Blades also allow for very few directions of movement and are only really designed to move vertically, while a spring and damper combination can be manipulated into a much larger range of motion. Leaf springs are tightly clamped and bolted to the chassis and clipped to the axle, leaving little or no room for other directions of movement, which can cause excessive wear on the pivots and linkages that hold the setup together.