A car’s suspension system plays a crucial role. It ensures that the vehicle keeps its wheels pressed against the road despite any surface imperfections while maximizing comfort for its occupants. Suspensions come in many different types, including torsion bars and coil springs.
Torsion bars are made from spring steel, allowing them to twist back into position. Because of that, they can apply torsion force to keep the vehicle’s wheels pushed down against the ground to maximize traction. Meanwhile, coil springs are made from metal twisted into a compact helix shape. They also perform a similar function, though they apply the same force vertically.
As you read through this guide, you’ll first learn about a car suspension system’s purpose. Then, you’ll learn the different ways that torsion bars and coil springs serve that purpose when installed in a vehicle, whether that’s a passenger car or a truck.
What Is The Purpose Of A Car’s Suspension System?
Torsion bars and coil springs are two versions of automotive suspension systems. So, before we dive deeper into how each one is unique, let’s get on the same page about their overall purpose and the reason your car has one or the other.
Generally, the purpose of a car’s suspension system is to keep all four of its wheels pressed against the ground at all times. From a technical perspective, that means the suspension helps to maximize each tire’s grip on the road by maximizing the friction it creates.
Despite how heavy a standard car is, keeping all four tires firmly pressed against the ground isn’t so straightforward. That’s because roads have imperfections like bumps which can briefly cause one or more tires to lift off the ground.
The same problem also happens when cornering, as the vehicle’s weight mostly leans onto the outer tires while taking that turn. Meanwhile, the tires on the inner side of that cornering lift off the ground slightly.
A suspension system, whether it uses torsion bars or coil springs, minimizes the problem described above. In doing so, it helps to keep all tires against the road as much as possible, regardless of the bumps in the road or the leaning that occurs while cornering.
The bottom line is straightforward: torsion bars and coil springs serve the same purpose, but they do so using different approaches.
We’ll take a closer look at each one in the following sections below.
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What Is A Torsion Bar, And How Does It Work?
A torsion bar is designed to fulfill the same suspension purposes described above. As the name suggests, the suspension benefits are provided by a metal bar and the torsion force it creates.
More specifically, it’s a bar made from spring steel that twists to keep the wheels firmly planted on the ground.
One end of the bar is attached directly to the vehicle chassis and kept in a fixed position. Meanwhile, the other end attaches to the wheel’s control arm, where it applies a constant amount of torsion force to keep that wheel pressed against the road underneath.
A car that uses a torsion bar suspension system consists of two metal bars stretching along the length of the vehicle’s body.
Suppose the vehicle’s wheels go over a bump or any other road imperfection that raises them off the ground. As that happens, those bars apply tension force in the opposite direction.
Doing so achieves the goal of the suspension system of maximizing each wheel’s friction and traction on the ground.
While all suspension systems improve comfort and handling, torsion bars are the preferred solution for cars designed to maximize comfort. They still provide handling benefits, of course, just less than other types of suspension systems.
Torsion bars aren’t as common on passenger vehicles as they used to be. However, you’ll still find some manufacturers using them in their commercial vehicles, like trucks and pickups.
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What Are The Downsides Of A Torsion Bar Suspension?
Torsion bars come with one significant drawback. Earlier, you read that they offer superior comfort to the vehicle’s driver and passengers, and that’s true.
Unfortunately, torsion bars aren’t good for reducing body roll or leaning. As a result, vehicles using this kind of suspension don’t handle very well when taking hard corners.
That’s one significant reason why auto manufacturers have gradually stopped using torsion bars as part of their designs. Instead, they’ve shifted to different suspensions, including independent coil springs.
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What Is A Coil Spring, And How Does It Work?
Coil springs form another type of suspension system that’s very common in everyday vehicles. With this setup, your vehicle’s wheel uses a vertical spring that has a spiral or helix shape.
As you can imagine, the spring provides a constant downward force that applies to your wheels, absorbing any shocks and keeping the tire firmly pressed against the ground.
Each spring is made from a metal bar twisted to form a spiral shape. That offers several advantages, namely in terms of saving space.
Earlier, you read that torsion bars stretch lengthwise across the vehicle’s frame. However, coil springs only occupy a vertical space inside the wheel well.
Besides that, a suspension system that uses coil springs is significantly lighter than one using torsion bars. That lightweight trait isn’t ideal for everyday passenger cars but also offers a significant advantage in motorsports vehicles.
Coil springs come in a variety of different options. Typically, you’ll differentiate them by diameter and length. However, depending on your intended application, you can choose springs with varying wire diameters, coil spacings, and different stiffness levels.
Choosing the best combination of those traits will ensure you achieve the desired outcome. For example, passenger cars will likely aim for more comfort, while motorsports vehicles prioritize handling instead.
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What Are The Downsides Of A Coil Spring Suspension?
Coil springs are a popular option in most vehicles. Still, they come with their fair share of drawbacks.
Firstly, coil springs aren’t as effective at load-bearing as other suspension types. That means they don’t work so well when there’s a lot of weight from above, i.e. the vehicle’s body.
As a result, they’re not a suitable option for heavier vehicles, such as those that haul a lot of cargo. For example, cement and garbage trucks are better off using other suspension options instead of coil springs.
Besides that, coil springs can also be more expensive, at least if you choose from a reputable brand. So, not only does that add to the price of a new vehicle, but it also makes spare part replacements quite pricey later.
Still, you need more control over the suspension manufacturers put in your chosen car. However, it’s wise to be aware of their limitations to plan ahead should any repairs or replacements become necessary.
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When it comes to suspension systems, there is no one-size-fits-all solution. Instead, each suspension is better suited for different applications and preferences.
For example, torsion bars provide excellent comfort to the vehicle and its occupants. That’s why they were once the preferred choice for passenger vehicles from leading auto manufacturers. Coil springs, however, are compact in size and offer better handling. As such, they’ve become the preferred choice over the years as manufacturers gradually phased out torsion bars from their designs.