Coil springs are used to absorb shock, maintain force, support structures and facilitate controlled movement in various mechanical applications. They can be used in a wide range of systems, from automotive components to industrial machinery.
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A coil spring is a mechanical device made from elastic materials, such as metal wire, coiled into a helical shape. This design enables the spring to compress, extend, or rotate under load and then return to its original shape once the load is removed. The properties of coil springs allow them to store energy temporarily and release it as needed, providing solutions for managing force and motion in mechanical systems.
A coil spring functions by resisting force through compression or extension, absorbing energy when force is applied and then releasing that energy to return to its original shape. This mechanism allows it to manage shock, maintain force and facilitate controlled movements in various applications.
The three main types of coil springs include compression springs, tension springs and torsion springs; each has different advantages and functions.
Compression springs store and release energy when subjected to a compressive force. As the spring compresses, it stores energy within its structure. When the force is removed, energy is released, and the spring expands to its original length. In their original state, compression spring coils have space between them; they absorb shock and maintain force between components.
Compression spring applications include automotive suspension systems, industrial machinery and valve and actuator systems. Other uses include everyday household items such as pens, door locks, mattress springs and buttons in electronic devices.
This type of spring, also known as an extension spring, works by resisting a pulling force. It absorbs and stores energy as it extends and then at a certain length, will create a return force and bring two components back to their original position. In their original, unloaded state, the adjacent coils will touch each other - however, the initial tension must be overcome before a tension spring extends.
Tension springs are used in a wide range of industries for products such as trampolines, retracting seat belts, garage doors, power tools, motorsport throttle linking systems, vibrating screens in mining, plus architectural designs.
Torsion springs function by applying torque or rotational force. They activate when a force is applied to their arms, twisting the spring. The energy stored during this twisting motion is released as the spring returns to its original position. They are ideal for applications requiring controlled, rotational movements.
Torsion springs are used in pegs for gripping clothes, garage door mechanisms for lifting and lowering the door, hinges to return doors to a closed position, mouse traps for the snapping mechanism, watches for the winding mechanism, and vehicle suspension systems for stabilising and controlling movement.
When designing coil springs for heavy-duty applications, it is important to consider factors that ensure durability, efficiency, and performance under extreme conditions. Applications demand springs that can withstand high stresses without failing, and so the choice of materials, as well as spring rate, is fundamental to product success.
Common materials used in the coil spring manufacture process include stainless steel, carbon steel, chrome silicon, chrome vanadium, Inconel, elgiloy, titanium, phosphor bronze and beryllium copper. Each material varies in its strength, elasticity, corrosion resistance, and fatigue life. For example, high-grade steel alloys are commonly used for their excellent tensile strength and durability. Whereas, materials like stainless steel are preferred for environments where corrosion is a concern. Nickel and galvanised steel coatings can then further enhance corrosion resistance.
The spring rate, or stiffness, indicates how a spring will perform under load. It is defined as the amount of load required to compress the spring by a unit of length. In heavy-duty applications, selecting a spring with the correct spring rate is essential to ensure that the spring can absorb the required forces without compromising its structural integrity or functionality. A higher spring rate indicates a stiffer spring, which is beneficial for applications involving heavy loads, but it must be balanced with the need for flexibility and shock absorption.
Coil springs are integral to heavy-duty machinery across various sectors, such as in the automotive, construction and agricultural industries. Let’s explore how they enhance performance, safety, and durability in these applications.
In the automotive industry, coil springs are used in car suspension systems to ensure vehicle stability, shock absorption, and comfort. They are designed to withstand the repetitiveness of daily use and harsh driving conditions across every vehicle type from domestic cars to heavy-duty trucks, buses, and off-road vehicles. Other uses include seat mechanisms, clutch assemblies, brake systems, engine valves and vibration dampening to reduce noise inside the vehicle.
Construction equipment relies on coil springs for vibration control and operational efficiency. They are used in machinery such as bulldozers, excavators, and cranes to absorb shocks, maintain equipment alignment, and reduce wear and tear, ensuring reliability and safety on construction sites. Other common types of uses include concrete mixers, truck tailgates and vibrating screens and feeders.
Agricultural machinery, including tractors, combines, and ploughs, use coil springs to manage the uneven terrain and heavy loads. They maintain stability, improve ride quality, and extend the lifespan of machinery in demanding environments. Other uses include tractor seats, baler machinery, and sprayer arms for crops.
Compression springs, tension springs and torsion springs can be custom-made and manufactured to your specific needs. Our advanced hot and cold coiling technologies and manufacturing capabilities enable us to coil springs from 3mm to 65mm wire diameter. Plus, our prototyping and sample services enable you to test your product before it goes into production.
Here is a quick overview of the process of designing a custom spring.
Our free consultation explores the application of your spring. We find solutions to questions such as ‘What is its failure mode?’ and ‘Are you looking to improve an existing design, or does it need to be lighter, stronger and more corrosion resistant?’
We explore limiting factors and evaluate the final dimensions, then create a suitable production drawing that meets all of your requirements.
We carry out material research, considering factors such as tensile strength, durability, efficiency and corrosion resistance, to find the best material for you.
Our spring technicians then develop a new coil spring design using the most advanced spring software programme - Optispring. Plus, we book a feedback session with you to evaluate the success of the design.
We deliver manufactured metal spring samples so that you can test them in real-world applications. This guarantees that you are happy with the spring and that it is reaching optimal performance before going into production.
Our quality team will then review various aspects of the process, including the initial drawings, testing procedures, powder coatings, and print markings, and then carry out the Almen Arc test. These steps ensure you are satisfied with every step of the approval process - and then production begins!
Coil springs are essential components in various mechanical applications in a wide range of industries. The three main types of coil springs are compression springs, tension springs and torsion springs - each works by resisting compression, extension or torsion forces. However, the main functions of all types of coil springs include shock absorption, maintaining force, supporting structures and facilitating controlled movement. It is important that materials and spring rates are considered for each type of coil spring during the design and manufacture process.
When we first introduced our Double Barrel Coil shock – The DB Coil – back in , you typically only saw coil shocks on bigger travel downhill bikes. These days, coil shocks (and springs) can be found on bikes that range all the way down to 120mm of rear wheel travel. Unlike air shocks, with coil shocks you need to physically change the spring to change the spring rate for different rider weights, which makes choosing the right spring a little more involved. So it’s no surprise we get asked a lot of questions about coil springs.
The goal of this article is to help educate you on some confusing shock terminology, and to help you identify how to determine the correct coil spring rate for any full suspension bicycle.
Finding the correct spring rate is important because it will help you achieve the appropriate sag amount. Sag is the first (and most important) step in tuning a rear shock – other shock adjustments like rebound and compression should not be adjusted without setting sag first. Before we tell you how to set sag, there are some concepts you should familiarize yourself with to help understand this whole process.
This is where the relationship between Rear Wheel Travel and Stroke Length comes into play. Leverage ratio is the ratio between how much Rear Wheel Travel your bike has per millimeter of Stroke Length
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On a full suspension bicycle, the rear shock is connected to a series of linkages that apply leverage to the rear shock. This leverage is applied to the amount of movement that the shock has (Stroke Length) and generates the amount of Rear Wheel Travel.
A good way to imagine this concept would be to think of a lever – you have a rigid bar that rests on a pivot point with one end of the bar that you input force into (your shock), and the other end of the bar is where the output force manifests (your rear wheel).
You can find your bike’s average leverage ratio by dividing the Rear Wheel Travel by the Stroke Length. For example, you have a bike with 160mm rear wheel travel with a shock that has a 60mm stroke length. 160mm wheel travel divided by 60mm stroke length is 2.67. This means your bike has a 2.67:1 average leverage ratio. So, for every 1 mm of movement on your shock, your rear wheel will move 2.67mm (on average).
It is important to note that your bike’s average leverage ratio is just that, an average. The leverage ratio will change as the wheel goes through its travel. If you were to plot the different leverage ratios as your wheel goes through its travel on a graph, you would see your bike’s leverage ratio curve.
Rear suspension is designed to incorporate an increase in resistance as you near the end of Rear Wheel Travel to help prevent harsh bottom outs. This increase in resistance can also be referred to as progression. Keep in mind that when we refer to rear suspension, we are referring to the rear shock AND the bicycle together, not one or the other on their own. Both the rear shock AND the bicycle can contribute in preventing bottom out.
It wouldn’t make much sense (or be that much fun) to ride a full suspension bike with no progressive rear suspension because the bike would bottom out on small bumps and provide no support on bigger hits. Think of jumping into a pool with water vs jumping into a pool with no water – with no water there’s nothing to slow down your momentum when you enter the pool, you just slam down to the bottom.
Coil shocks (and coil springs) are linear by nature – this means the amount of force required to compress the spring will increase linearly. A 400lb coil spring will require 400 lbs to compress the spring one inch, and 800 lbs to compress the spring two inches, and so forth.
Air shocks (and air springs) are progressive by nature – this means the amount of force required to compress the air spring will increase exponentially. With air shocks, the air spring is housed inside of an enclosed air chamber. As the air spring compresses, the amount of volume in the air chamber will decrease, which compresses the air molecules making it harder and harder to compress the shock.
In this regard, you could sensibly pair a coil shock with a linear spring with a bike that has a significant amount of progression built into the suspension design, because the progression is occurring through the bike design. And vice-versa, you could sensibly pair an air shock or a coil shock with a progressive coil spring, with a bike that does not have as much progression built into it because you are getting the progression from the air spring or the progressive coil spring.
Now we are getting into what you’ve come here to learn! To determine which spring rate you need, there are three main factors to identify: rider weight, the bike’s leverage ratio, and riding style.
It is a good idea to contact the manufacturer of your bike to see if they can recommend a spring rate for your specifications, but you can also calculate this on your own, and below we lay out two ways you can calculate this. Keep in mind riding style is subjective, and the goal of these calculations is to help you determine a spring rate that will get you to correct sag, and it’s up to you to consider your riding style.
These calculations apply to both e-bikes and non e-bikes. A common misconception is that the rider will need to go up in spring rate simply because of the extra weight of the e-bike.
The second way to calculate your Spring Rate would be to use your bike’s average leverage ratio. This method is less accurate, but will still provide a good place to start. You could use this method if you are unable to find your bike’s leverage ratio curve, or reach the manufacturer.
For this example we’ll use a bike that has 150mm of Rear Wheel Travel with a 210X55mm shock size, and a rider weight of 185lbs (175lb rider wearing 10lb of gear)
Step 1 – Determine your bike’s average leverage ratio by dividing Rear Wheel Travel by Stroke Length. 150/55 = 2.72
Step 2 – Multiply the average leverage ratio by your rider weight. 2.72 X 185 = 503.2
Step 3 – Consider your riding ability, locality, and style. This step is the most subjective. Below are some spring rate recommendations based on different types of riders:
Type 1 Rider (you’re new to mountain biking and want to try a coil shock) – Go with the closest spring rate to the spring rate calculation and allow room for preload. In this case a 500lb standard VALT spring would be a good place to start.
Type 2 Rider (you’re an intermediate mountain biker that hits features like drops and jumps with confidence) – A 500lb standard VALT spring would also work in this case – we would recommend increasing your compression damping to help combat harsh bottom outs. A 500-610lb progressive VALT spring could also be considered if the bike was in need of more progression or if your riding style dedicated the extra progression.
Type 3 Rider (You’re an advanced rider, you hit big drops and gaps, you send it) – In this case we recommend that you start with the 500-610lb progressive spring to help support you when landing. You could also consider a 550lb standard VALT spring if you did not need the extra progression, or if your bike was extremely progressive.
We sometimes hear confusion surrounding this terminology – the misconception is that linear leverage ratio bikes would be compatible with linear springs, and progressive leverage ratio bikes are compatible with progressive springs. In fact, in most cases it is quite the opposite. In the section above “What Does Leverage Ratio Mean” we explain that there must be some sort of resistance (progression) incorporated into the rear suspension in order to support your riding and prevent harsh bottom outs.
If you have a linear frame, you can sensibly pair that with a shock that is progressive (an air shock or a coil shock with a progressive spring), and if you have a progressive frame, you can sensibly pair that with a linear shock (coil shock with a linear spring).
With progressive springs the spring rate will actually increase, or become more progressive, at some point throughout the stroke of the spring. This progressiveness is similar to the ramp-up of an air spring. With our Progressive Rate VALT spring, we matched the spring curve of our Coil IL with a normal amount of volume reduction, which was calculated to be an 18% increase in spring rate at the end of stroke.
With linear springs, the spring rate does not change. The amount of force required to compress the spring per inch will increase linearly.
When it comes to choosing between a progressive or linear spring, your bike’s leverage ratio curve will influence the majority of this decision, but you should also consider your riding style. If you have a leverage ratio curve that is extremely progressive towards the end of its stroke, you may not want to choose the progressive rate spring. If you have a bike that does not have as much progression built into it and you want to use a coil shock, then a progressive rate spring could be a good choice.
The advantage of a progressive spring is that you get the off the top suppleness that coil shocks are known for, while still having that extra support / progression at the end of travel. Progressive springs also open up the possibility of using a coil shock on a bike that was previously not very compatible with a coil shock.
The spring size is directly related to the size of your shock’s Stroke Length. If you have a spring that is too long, it may not physically fit onto the shock without compressing the spring, and if the spring is too short, you risk not being able to use full travel.
Ideally you would use a spring length that matches the shock’s Stroke Length. For example, with a 210 x 55mm shock size, you would use a spring that has a 55mm Stroke Length. In some cases, you might have a Stroke Length that does not exactly match up to the spring length – that’s ok. You can factor in 2-5mm of difference between the labeled spring size and the Stroke Length. (a 200x57mm shock size would work on a 55mm spring).
If you intend on using a different manufacturer’s spring on your shock, The inner diameter of the spring has to be compatible with your shock damper body diameter. A spring with a 30mm inner diameter will not fit on a shock damper body that has a 35mm diameter.
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