Introduction

Today’s automobiles can be considered a culmination of industrial design. A car can be divided into three main systems:

  • Powertrain
  • Chassis
  • Body

The suspension system to be introduced in this article belongs to the chassis system. The primary function of the suspension is to provide ride comfort. In other words, in the face of various road conditions, the suspension system must strive to maintain stability to achieve the goal of providing comfort. The main components of the suspension system include control arms, shock absorbers, springs, anti-roll bars, and more. With the coordinated movement of these parts, the suspension system can respond to the challenges posed by different road surfaces.
It’s important to note that the classification of the chassis and suspension is somewhat ambiguous. Each component also has many different names, depending on the car manufacturer, country, producer, modifications, literature, and various sources, leading to different definitions. Individuals in related industries often have varying perspectives. Therefore, it’s not necessary to get overly caught up in classifications and names; a basic understanding is sufficient.

History and function

To understand the automotive suspension system, starting from the perspective of human history can help us better grasp the function of the suspension system.

The Starting Point of the Carriage Era

The concept of automotive suspension originated in the era of horse-drawn carriages. In the early days of horse-drawn carriages, before the invention of suspension systems, the wheels were directly fixed to the carriage body through the axle. Essentially, it was a box with wheels, providing a convenient means of transportation but lacking in comfort.

This design meant that all road conditions were directly transmitted to the carriage body. Whether encountering potholes, uneven terrain, or turns, every movement experienced by the wheels was conveyed unabated into the cabin.

At this point, the function of the suspension system becomes evident—by reducing vibrations transmitted from the road to the vehicle body.

  • Enhance the comfort of the passenger.
  • Reduce wear and tear on the vehicle’s body structure.

As time progresses, the understanding and development of suspension systems continue to deepen. In modern automobiles, the functions performed by suspension systems can be generally classified into the following:

  • Enabling Vehicle Movement, Braking, and Steering
  • Maintaining Road Contact During Driving
  • Reducing Road-Induced Vibrations for Improved Comfort
  • Supporting Vehicle Weight
  • Limiting Tire Displacement for Increased Handling Limits and Driving Safety
  • Facilitating Power Transmission to the Road

Spring: Springs are the core components of the suspension system, and their primary function is to support the weight of the vehicle and absorb road vibrations. They can be broadly categorized into three types

  1. Torsion Bar (Not torsion beam)
    A slender rod-shaped component is positioned parallel to the vehicle body. It is nearly obsolete in modern vehicles, with only a few using this design.
  2. Leaf Spring
    Composed of multiple thin, elongated steel plates stacked together and secured with shackles. The number of leaves can be adjusted by the manufacturer based on the vehicle’s load requirements. Commonly found in vehicles that need high load-carrying capacity or some off-road vehicles.
  3. Coil Spring
    A spring with a coiled, spiral shape, similar to the commonly seen springs. Over 80% of vehicles use this type of spring, making it the most widely used in contemporary suspension systems.

Damper:
The main function of the damper is to absorb and control the vibrations of the spring, and it is not responsible for bearing the weight of the vehicle body.

Control Arm:
The control arm connects the steering and the vehicle body to control the range and direction of tire movement, allowing the vehicle to travel smoothly on the roadway. The control arm is comprised of a ball joint and a bushing, available in various shapes, depending on the designer’s desired outcome.

Sway bar links:

As the name suggests, this component is used to connect the anti-roll bar and usually does not come with additional functions other than the connection. One end is linked to the anti-roll bar, and the other end, based on the manufacturer’s design, may be connected to the control arm or damper. For modified cars, this is an essential part.

Sway Bars:
The stabilizer bar primarily functions to enhance the rigidity of the vehicle during lateral tilting, improving the stability of the vehicle during turns. Typically, it forms a “U” shape, and there are rubber bushings at both ends. The sway bar utilizes the twisting action through these bushings to exert its effect. When there is a difference in height between the wheels on both sides (occurs during rolling), the “torsion” phenomenon acts on the U-shaped bar, attempting to keep both tires as level as possible.

Joint and Bushings:

The components mentioned above are all made of metal. To ensure that all components work together, they need to be interconnected. However, if they are simply fastened with screws, direct metal-to-metal friction can lead to noise, reduced ride comfort, and wear. Therefore, we need bushings to serve as intermediary connecting components. The bushing has a ring-shaped structure, with an outer layer encapsulating rubber, which in turn encases an inner tube. With this construction, when the components are fastened, the rubber can effectively absorb shocks, providing a more comfortable riding experience.

Ball Joint:

A ball joint is a spherical structure located at one end of the control arm, connected to the steering knuckle. When the tie rod moves, it causes the steering knuckle to turn. If the endpoint of the control arm connected to the steering knuckle is locked, steering cannot be achieved (similar to joints in the human body). The quality of the ball joint is a significant factor in determining the vehicle’s handling. As mentioned earlier, the control arm controls the position of the tires, and the ball joint is crucial. It needs to withstand various forces from the tires and consistently control the tire’s movement within a specified range.

  • Steering: Requires a 360-degree range
  • Tire Travel: Acceleration and deceleration.
  • Elasto kinematics: Forces, deformations, and changes in rigidity brought about by various connection points.

Types of Suspension Systems

The suspension system can be classified in various ways, and the following attempts to list different methods of classification and provide simple explanations. However, due to the multitude of design approaches and the modifications made by different manufacturers, new suspension classifications may arise as variations of existing designs, sharing similar underlying principles.

Therefore, explaining it comprehensively is not easy. The design of a suspension system is not inherently good or bad; it depends on the requirements set by the manufacturer for a particular vehicle. Factors influencing the design include cost considerations, geometric structure, the intended purpose of the vehicle (comfort, sportiness, or load-bearing capacity), collaborative development, market acceptance, and more.


The configuration of a suspension system is generally determined by three main components:

  • Spring
  • Control Arm
  • Vehicle Structure

To clearly describe the suspension structure of the vehicle, it can be categorized into the following types. Some can be combined, while others cannot, and there are also hybrid forms. The following are common configurations:

SpringControl ArmStructure
Circular SpringMacPherson strutTorsion Beam
Leaf springDouble WishboneSolid Axle
Torsion barMulti-linkSwing Axle
Air springTrailing Arm 
 Semi-trailing Arm 

Independent/Non-independent Classification

IndependentNon-independentSemi-Independent
Double WishboneSolid AxleTorsion Beam
Multi-Link  
MacPherson Strut  
Trailing Arm  
Semi-trailing Arm  

Front and Rear Axle Classification

FrontRear
Double WishboneSolid Axle
MacPherson StrutTorsion Beam
Multi-LinkTrailing Arm
 Semi-trailing Arm
 Multi-Link
 Double Wishbone

The common classifications and types of suspensions listed above will be used to explore the differences in characteristics among various suspensions based on actual car models.

Double Wishbone
F/ Ferrari 812 superfast

F/ BMW 7-Series (G70)

Muli-Link
F/ M-Benz S-Class (W223)
R/ Alfa-Romeo GIULIA (952)

MacPherson Strut

F/ HONDA CR-V (6th Gen)

F/ NISSAN X-TRAIL(T33)

Torsion Beam (often combined with trailing arms)

R/ TOYOTA COROLLA(E210)*

R/ PEUGEOT 208(P21)

Solid Axle

R/ FORD F-150(14th Gen)

R/ GMX SIETTA 1500(5th Gen)

** In 2023, the Toyota Corolla underwent a rear suspension change, transitioning from a double-wishbone setup to a torsion beam.**

By the aforementioned models, we can clearly understand the features of various suspensions. However, some models have interesting suspension configurations, often different from our perceptions. Here are three models. Interested individuals may consider why the manufacturers designed them this way.

  • Porsche 911 GT2 RS(991.2)—F/ MacPherson

In 2018, it set a record at the Nürburgring Nordschleife, becoming the fastest production car (until in 2023.)

  • TOYOTA corolla(E210)—R/Torsion Beam
    In 2019, the all-new facelift Corolla abandoned the previous torsion beam design for the rear axle, opting for a double-wishbone suspension. However, in the 2023 redesign, the double-wishbone setup was discontinued, and the torsion beam configuration was reintroduced.

Conclusion

The above briefly introduces the basics of the suspension system, from historical development, and component explanations to the forms of suspension systems. Each component of the automotive suspension system plays a crucial role in the overall performance of the vehicle and the comfort of the driver and passengers. Regularly inspecting and maintaining the suspension system is the key to ensuring driving safety and enhancing the driving experience. Hoping that reading this article has given you a preliminary understanding of automotive suspension systems.

Reference

●    Chassis Handbook Bernd Heißing, Metin Ersoy (2010)

●    自動車のサスペンション KYB株式会社 (2013)

●    車両運動性能とシャシーメカニズム 宇野高明 (2022)

●    Official information from major automotive brands’ websites

●    Internal data from TGQ