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Suspension: A Brief History and Purpose
Although the first modern car was invented by Karl Benz in 1885—more than 130 years ago—the concept of suspension goes back much further, all the way to the era of horse-drawn carriages. In fact, ever since the invention of the wheel, people have been working to improve ride comfort and control through suspension systems. Today, that long journey of innovation has brought us to the point where race cars can take corners at speeds over 180 mph.
Why Suspension Matters
The purpose of suspension is simple: to improve comfort and handling. Think about the vibration you feel when pushing a shopping cart across the Walmart parking lot—that shaky, rattling sensation. That’s what it feels like to drive without any suspension. Now imagine feeling that on every bump in your car. You probably wouldn’t last even a mile before wanting to get out.
Evolution and Components of Suspension Systems
Over time, suspension systems have evolved into many different forms. They usually consist of a subframe, suspension arms, springs, and axles. By changing the type or layout of these parts, we can create different suspension setups to meet various needs. In this article, TGQ will walk you through some of the most common suspension types, along with their pros and cons. And maybe next time you’re buying for a car, you’ll think about more than just screen size and ACC —suspension might become part of your checklist, too. (Even if you’ll probably never see it)
Suspension classification can get very complicated. In fact, just a small change to a single part is sometimes enough to make it a “different type” of suspension. On top of that, many automakers give their suspensions flashy names for marketing purposes—even when the systems themselves aren’t that different. So, it’s nearly impossible to create a perfectly clear and universal classification. But we’ll do our best to break it down. Generally speaking, suspension systems can be divided into 4 major types.
- Non-independent suspension
- Semi-independent suspension
- Independent suspension
- Strut-type suspension
Non-independent suspension
Also known as rigid suspension or solid axle. It refers to a design where the left and right wheels are connected by a single metal rod. When one wheel moves, the other moves as well due to this connection. This type of suspension can be paired with coil springs, leaf springs, or torsion bars.
Upsides
- Low manufacturing cost
- Low maintenance cost
- High load-carrying capacity
- Excellent off-road capability
Downsides
- Poor ride comfort
- Poor drivability
Solid axles have clear characteristics, so vehicles equipped with solid axles usually have specific purposes. Usually, the front axle of a vehicle does not use a solid axle because of poor handling. As vehicle weight, power, and safety requirements continue to rise, so does the demand for better handling. Therefore, the front axle, which is responsible for steering, typically does not use a solid axle.
On the contrary, the rear axle generally has lower handling requirements, and solid axles can provide good load-carrying capacity. That’s why many vehicles use solid axles on the rear.
Vehicles with Solid Axles
1. Jeep Wrangler
Front solid axle / Rear solid axle
The most iconic off-road vehicle in the world, it uses solid axles on both front and rear to deliver the strongest off-road capability.
2. Chevy Silverado
Front independent / Rear solid axle
A best-selling pickup truck. To meet comfort needs for city driving, it uses independent suspension on the front axle. But for the rear axle, to handle load-carrying demands, it adopts a solid axle.
3. Camaro (before 2002)
Rear solid axle
A classic pony car that surprisingly used a solid axle despite being a sports coupe. This contradiction contributed to Camaro’s poor handling. That’s also why many people have a bad impression of American pony cars’ handling, thinking they’re only good for drag racing. Fortunately, since 2010, both Mustang and Camaro—and all pony cars—have switched to independent suspension to improve handling.
Semi-independent Suspension
There are many types of semi-independent suspension. Among them, the most important is the torsion beam, as it is the most commonly used type and others are derived from it. Many people confuse this suspension with non-independent suspension because non-independent suspensions have almost disappeared from passenger vehicles. Over time, semi-independent suspensions have come to be seen as non-independent.
The torsion beam suspension’s structure is actually similar to non-independent suspension, as both are connected by a main metal component.
Torsion Beam
The torsion beam suspension is made from a U-shaped steel beam. The top of the U is connected to the vehicle body via bushings, while the lower ends of the U connect to the wheels. After the torsion beam connects to each wheel, it extends forward toward the front of the car, then bends sideways to link both wheels together. This extra part lets the metal twist a little bit, so the two wheels can move somewhat independently instead of being completely locked together. Therefore, the relationship between the two wheels is neither fully independent nor fully dependent, hence the name semi-independent.
Upsides
- Cost-effective
- More cabin space
- Acceptable handling
- Acceptable ride comfort
Downsides
- Acceptable handling
- Acceptable ride comfort
The key feature of semi-independent suspension is that it achieves a balance across various suspension aspects. Because of this, torsion beam suspensions are widely used in today’s cars, including brands like Mercedes, Ford, and Toyota. They are especially common in Japanese cars and hatchback models.
Moreover, since torsion beams can’t meet the demands of precise cornering, they are usually only found on the rear axle. It’s worth mentioning that French automakers particularly favor torsion beam suspensions and often tune them to deliver a fascinating driving experience.
Cars Equipped with Torsion Beam Suspension
- Mercedes A-Class (Entry trim)
Although it’s a Mercedes, the A-Class serves as an entry-level model for the brand, so it comes equipped with the more affordable torsion beam suspension. However, for higher-performance models like the A250 and AMG 43, to match their powerful output, independent suspension is used instead. - Toyota Corolla (Entry trim)
As the world’s best-selling car, the Corolla offers a well-balanced performance in all aspects, which is why it uses the balanced torsion beam suspension. - Peugeot 208
Independent Suspension
Independent suspension means that when a vehicle’s wheels pass over uneven road, the movement of one wheel does not transfer to the other side. In other words, each wheel can move independently. This design offers many benefits, including improved handling and ride comfort. However, it also has some drawbacks.
The key feature of independent suspension is that each wheel is connected to the car’s main body through its own suspension arms (also called control arms). With the advancement of modern vehicle chassis technology, independent suspension has evolved into many different forms, and there are significant differences among these types.
Below, we will introduce several of the most common types.
Trailing Arm
A trailing arm is a long link that runs roughly parallel to the car’s body. Each wheel has its own trailing arm. One end of the arm is rigidly connected to the wheel carrier, while the other end connects to the car body through a joint. Trailing arms are mostly used on the rear axle. When the suspension moves, the trailing arm behaves somewhat like it is “towing” the wheel.
Trailing arms provide a fairly balanced performance and share similar characteristics with torsion beam suspensions. For this reason, trailing arms are usually used on the rear axle of small cars, just like torsion beams.
Double Wishbone
Double wishbone suspension consists of two V-shaped suspension arms. The bottom of the V connects to the wheel carrier, while its two top points connect to the body. The lower arm is also V-shaped, with its base connected to the bottom of the wheel carrier and the two top points connected to the body. The upper arm is always shorter than the lower arm, so this setup is also called a short-long arm suspension.
Because double wishbone has distinctive features, vehicles using it tend to be quite consistent. It’s worth noting that nowadays, double wishbone suspensions have almost disappeared in European cars, usually replaced by multi-link setups. Double wishbone is now more common on pickups.
Upsides
- Great drivability
- Great ride comfort
Downsides
- High cost
- Takes up considerable space
Multi-link Suspension
As the name suggests, multi-link suspension uses multiple links—usually between three to five—to control the wheel’s motion. This type of suspension separates all the chassis geometry, dynamics, and kinematics into different components and designs each one individually. Because of this, every automaker has its own design method.
We won’t go into all the details here since there are so many variations, but we will explain the common features of multi-link suspensions.
As mentioned earlier, this suspension distributes the forces that the chassis may encounter to different links. The advantage is that engineers don’t have to worry about each part handling all the forces; instead, they can design each part specifically for certain loads. This results in excellent drivability and ride comfort. However, it also means higher costs.
If you take the lower “V”-shaped link of a double wishbone suspension and split it into two “I”-shaped links, you get a setup with two lower links and one upper link, known as a three-link multi-link suspension. European luxury brand engineers favor this design, which is used in models such as the Mercedes S-Class and BMW 7 Series. Audi goes even further by splitting the upper “V”-shaped arm into two links, creating a four-link multi-link suspension.
Multi-link suspensions use the cooperation of multiple links to allow engineers to precisely control wheel angles such as camber and toe under various loads, which improves handling performance.
Examples of Multi-link Suspension
- 3-link multi-link: Land Rover Range Rover (L460) — Front
- 4-link multi-link: Audi A4 (B9) — Front
- 5-link multi-link: BMW 1 Series (F20) — Rear
Upsides
- Great drivability
- Great ride comfort
Downsides
- High cost
- Space-consuming
Strut-type Suspension
Last but not least, the strut type suspension, also called MacPherson suspension, is a very unique design system. It is composed of two major parts: the lower arm and the strut. The lower arm functions just like the suspension links in other systems. The strut is very special because it can simultaneously allow vertical movement and rotation. Vertical movement is necessary for the vehicle to move smoothly on the road, while rotation allows the vehicle to turn. Moreover, the strut can also act as both a damper and a spring (shock absorber).
The strut system can handle vertical displacement, rotation, shock absorption—all at the same time. This means that with only two parts, the suspension system can be complete. Therefore, it saves a lot of space for the engine, transmission, gearbox, cabin, steering, etc. As a result, nowadays over 60% of passenger cars use strut suspension on the front axle.
Notably, because the strut allows rotation, it only appears on the front axle.
However, luxury brands often use different names for strut suspension in their brochures for marketing purposes. For example, BMW 3 Series calls it the “Double-joint spring strut axle in lightweight aluminum-steel construction,” while Mercedes A-Class refers to it as “lowered comfort suspension.”
Upsides
- Acceptable drivability
- Acceptable comfort
- Excellent space utilization
- inexpensive overall cost
Conclusion
Non-independent, semi-independent, independent, and strut suspensions are the most common suspension systems today. Each has its own strengths and trade-offs, affecting ride comfort, handling, and cost. Understanding these differences can help you make better-informed decisions when choosing or evaluating a vehicle.
TGQ R&D hopes this introduction helps everyone better understand the different types of suspension systems. Springs, an equally important part of suspension, will be discussed in a future chapter.
References
- T.G.Q R&D
- T.G.Q Sales
