Working together to absorb impacts and help keep the tires in contact with the road, coil springs and shocks/struts are key parts of a vehicle’s ride control system. Made of wound metal, coil springs are designed support the vehicle’s weight. They compress and absorb road impacts, allowing the frame and body of the vehicle to experience minimal disturbances when riding over bumps such as railroad tracks or dips such as potholes. Coil springs also help prevent the vehicle from bottoming out when loaded or during adverse driving conditions by working to maintain optimal ride height as determined by the manufacturer.
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Replacing the coil springs on a vehicle can have a dramatic impact on its ride and handling. From matching OE performance to achieving improvements in performance, using the right coil spring is vital.
Coil springs have a direct effect on the ride profile of a vehicle. Several factors contribute to how a coil spring will perform on a vehicle:
A poorly engineered constant rate spring with too many coils can cause coil bind, a condition where the coils stack solid at or before full suspension compression. This can lead to suspension component damage.
A spring made from higher grade steel with quality coating like urethane or epoxy helps increase the durability of the spring. Bare steel or coils that are painted may not last as long as coils with a quality coating that helps keep the steel from rusting.
The spring rate increases with a higher wire diameter. However, higher grade steel in combination with a smaller wire diameter can handle heavier loads.
There are two main types of coil springs – constant rate coil springs and variable rate coil springs.
Also known as linear rate springs, these springs feature evenly spaced coils for a uniform rate of compression. The spring compresses an amount proportional to the load being placed on the spring. Popular for heavy-duty and performance applications, when the correct constant rate spring is chosen it helps improve ride quality by reducing pitch and roll.
Also known as progressive rate springs, these springs have coils that aren’t evenly spaced out. The spring rate changes dynamically as the spring is compressed, allowing it to have different spring rates. The coils that are spread apart provide a comfortable ride under normal conditions and when the vehicle is loaded, those coils become compressed. The tighter wound coils help prevent the vehicle from sagging excessively. Ideal for multipurpose vehicles used as daily drivers as well as hardworking activities like towing or hauling loads, variable rate coil springs can help reduce harshness and pitch and roll, and help avoid bottoming out under various levels of load conditions.
Also known as deflection rate, spring rate is a measure of a spring’s strength and is determined by the wire diameter, number of coils and quality of the steel. It is the amount of weight needed to compress the coil spring one inch. The OE spring rate can differ from one vehicle to another based on vehicle model, engine size, drivetrain (4W vs front wheel), transmission type (automatic vs manual), and other vehicle attributes that affect vehicle weight and ride profiles. In fact, within a single model, there can be different packages and trim levels that can affect spring rate.
It's important to match OE spec by application when it comes to spring designs to help restore OE ride height specifications assigned to each vehicle. Even a 15% reduction in ride height can cause the vehicle to noticeably sag and may affect wheel alignment which could result in accelerated tire wear.
Here are some additional things to know:
A spring manufacturer can use its own formula to achieve the spring rate; they can alter the steel strength, wire diameter or number of coils to do so. Simply adding more coils to compensate for lower strength steel may not match the OE spring rate. The additional coils can stack up, creating touchpoints of the coils at or before full suspension compression and causing coil bind, potentially resulting in immediate suspension component damage.
Spring rates can differ from the left side of the vehicle to the right. The design of the vehicle is a major factor in how the manufacturer determines the proper spring rate for each side. For example, many vehicles have the engine offset to the passenger side to make room for components like the accelerator and brake pedal. This can affect the spring rate of the right and left side of the vehicle. It is important to take this into consideration when it comes to individual coil springs or as part of a strut assembly - not matching the OE spring rate could compromise the vehicle’s performance.
Diagnosing if the coil springs are worn is the first step; check out this ServiceGram for guidance.
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Designed specifically for hardworking half-ton trucks and vans that haul and tow, you get everything you need for a strut replacement in a single, fully assembled unit. Features a variable rate coil spring that delivers a comfortable ride and helps reduce sag when under load.
Ninety percent of the performance and feel of your suspension comes from having the proper spring and shock combination. But what contributes to the perfect combo? There’s no one-size-fits-all solution, as drivers have varying needs and expectations, and there’s a lot to consider. That’s why it’s critical to understand the relationship between your suspension system and shocks and springs. Because whether you’re driving a dirt late model car, motorcycle, truck, or mountain bike, without the right combination, it can get bumpy, expensive, and potentially dangerous.
Your suspension system consists of a number of different components, but the most important pieces are springs, shocks, and tires. When these components are working together, drivers can easily maintain control over their vehicles. However, when drivers either don’t have the correct components in place or attempt to use their vehicle in a way that the current suspension system does not support, you’re going to have problems.
The correct suspension for any vehicle is important because roads are susceptible to hazards, including potholes, loose gravel, branches, and much more, putting unprepared drivers at risk. In areas prone to extreme weather, there can be even more challenges on the road. When you consider additional needs to adjust the suspension, such as in competitive drag racing with a car or a motorcycle, the suspension becomes even more complicated. However, with the right setup, drivers can find the right balance for them and gain a significant competitive edge from the proper suspension behavior.
Springs are one of the most crucial parts of your suspension setup. They determine how close or far your chassis sits from the road or track. Adjusting the springs helps prevent bottoming out, limiting body roll when accelerating and cornering, and limiting nose-diving when braking. They are essential in determining how your car handles. The shocks (dampers) help to manage and restrict the motion of the springs, absorbing the impact on their behalf. This means that springs that are too stiff, for example, may not be the best for drivers looking to handle their car in bumpy conditions.
By learning how shocks and springs work together, drivers and riders can better understand their unique needs and begin to experiment and adjust to get the ideal suspension for a competitive edge. The correct suspension can also serve drivers who love to get off the road and out on the trail, helping them to access better courses and maintain the durability of their bike, Jeep or SUV. At the very least, the right suspension and regular maintenance of your vehicle contribute to a smoother ride and help to avoid unnecessary expenses. A suspension that is not working properly can cause parts to wear out prematurely and require replacement. Wearable items like bushings and tires can all wear much quicker on vehicles where the suspension is not working properly.
In this piece, we will be covering:
The springs, in some form, have likely been used for thousands of years in vehicles and even devices such as the bow and arrow. Thanks to the research of a philosopher named Robert Hooke and “Hooke’s Law,” the world would eventually learn that when stress applied to a body goes beyond a certain value (the elastic limit), once the stress is removed, the body does not return to its original state. This eventually contributed to the invention of the first coiled spring in by R. Tradwell.
Since then, the basic design of the spring has changed, as well as the materials used to create a spring. The modern spring is essential to the suspension system, as springs store mechanical energy and support the weight of the vehicle.
In addition to having springs made from alternative materials such as carbon, air, and other designs, the different types of springs that you find in vehicles include:
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Here are a few examples of spring designs and where and how they are currently used, as well as some advantages and disadvantages of each.
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Leaf Springs, an early design of springs, were initially just stacked metal that was bent to produce a spring rate. In the Roman era, leaf springs were used in chariots and, eventually, in the early vehicles that came off assembly lines. Still today, some manufacturers use this spring technology to support commercial vans, trucks, trailers, and other vehicles. There are also a variety of types of leaf springs, such as elliptical leaf springs, semi-elliptical, three-quarter elliptical, quarter leaf, and more.
Typically, fitment can be a big reason to use this design. If you look at a coil spring vs. a leaf spring, you will notice the leaf spring is a much flatter design that doesn’t take up much space vertically. This can be an advantage when designing and space is limited. They can also provide more support to larger vehicles.
However, there are disadvantages to leaf springs. They don’t provide a lot of flexibility and can be challenging to make changes to. For drivers who want to experiment with different suspension setups, leaf springs may not be the best match. Additionally, there can be a lot of friction between each leaf, and in time, leaf springs can lose their shape. Traditional springs, such as coil springs, may last longer, depending on the circumstances.
Coil springs are round pieces of steel that are wound into a coil and are used in most cars and vehicles. Based on how a suspension is working or the packaging constraints, a coil spring is a more efficient option when compared to other spring designs.
Similar to leaf springs, the coil spring gives designers another level of freedom when designing a suspension. The thickness of the coil (diameter), how many coils, and the diameter of the spring all affect the rate of the spring. Some applications utilize multiple coil springs stacked on top of one another, as a stacked spring will produce a softer spring rate. For example, when stacked together, two one hundred pound springs will produce a rate of fifty pounds. This would be a basic and pretty simple stack.
The formula for figuring out your stack is: (S1xS2)/(S1+S2).
Example: (100x100)/(100+100)=50 lbs.
When you run an inner lock nut or cross-over, things can get more complicated. This allows you to start with a softer rate of 50 lbs initially. Now, if you run an inner nut, when one spring comes into contact with that inner nut, you can transfer and only work on one spring, which is now 100 lbs. So you go from a 50lb/inch rate to a 100 lb/inch rate. You’re now utilizing a progressive spring rate which is a significant advantage in certain applications.
Bump rubbers have been around since we have been riding around on two or four wheels and have evolved over decades of development. Bump rubbers are typically round-shaped pieces of foam or rubber; the average is about two inches tall that is used as an anti-bottoming tuning tool. The bump rubber absorbs shock and provides extra cushion while protecting the vehicle, preventing contact between the tires and fender, for example. Over the years, especially in racing, these have become essential pieces to tuning a car or motorcycle suspension.
As discussed, coil springs produce a linear rate throughout their travel until they “coil bind” or run out of travel. At this point, your suspension would go completely solid. If you can imagine your suspension moving through travel, nice and compliant, then in an instant, solid/no movement, you can see how bad that would be for handling and feel.
Typically installed on the shock shaft, bump rubbers can also be installed on another part of the suspension that will engage before fully bottoming out. They are typically very stiff compared to the spring rate, and they are usually at a progressive rate. So, the first half inch of travel has less rate than the last half inch of travel. While bump stops are important for all vehicles, they are especially important to protect them from rough terrain and prolong the life of various suspension components.
Shocks tame the oscillating effect of your springs as they store and release energy. As the primary function of shocks is to control how fast wheels go up and down, well-maintained shocks can give you the leverage to win a race or the ability to drive on varying terrains. However, as shocks are just a part of the suspension puzzle, having them in your vehicle doesn’t mean you’re going to necessarily have smooth sailing.
Drivers can experiment with different factors, such as their damping rate, to gain better control over their car. These adjustments can prevent oversteer or understeer, loss of traction, jarring movements, nose dives during braking, and more.
The different damping levels and curves include:
In this section, we will cover different damping levels and explain how they relate to overall suspension, but more importantly, how they can assist in the performance of the spring.
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Compression is when the suspension compresses. Therefore, your spring is compressing. This creates more load at a linear rate while traveling. Springs create force based on displacement or travel, and shocks produce more force based on velocity or the speed at which it’s moving. If you preload 250 lb spring two inches, you should produce 500 lbs of force sitting statically.
Now, if you take a shock and you do the same thing, the shock will produce no force statically regardless of its position. The shock will only produce more force if the speed of the movement is increased. This is the velocity and is usually measured in inches per second or millimeters per second. So, if you increase compression damping, it will slow or reduce the amount of compressed travel a suspension will travel. When done correctly, compression damping can help resolve common racing suspension issues, such as instability and rough rides.
Compression and rebound both impact how well you can handle your vehicle. While compression helps control the suspension as it compresses, the rebound does the exact opposite. Remember, as a spring compresses, it creates more load or stores energy. That energy must be released, which is the rebound. If you had no rebound in the shocks, it would allow your suspension just to continue to bounce on the spring. You need to rebound from the shock to control and ultimately settle your suspension.
Generally, the stiffer the spring rate, the more rebound you will need to control the increase in force or energy the spring produces. Again, like compression, this sounds simple, but there are many factors and tuning options in the rebound that will help you enhance and maximize your suspension’s performance. With the right approach, you can improve your vehicle’s traction and feel more control and comfort behind the wheel.
Types of Damping Curves
Compression and rebound damping can assist with spring rate and ultimately work with your spring to define your suspension character. Now, we will preview a few different types of damping curves and how they can affect the performance of your suspension.
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