Suspension Systems

ASHWANI KUMAR on 4/23/2021 12:23:32 PM

What is suspension system?

An automotive suspension connects a vehicle’s wheels to its body while supporting the vehicle’s weight. It allows for the relative motion between wheel and vehicle body.The suspension is responsible for carrying vehicle weight, absorbing road shocks, providing a smooth ride, and allowing good handling qualities.The suspension system contains three major parts: a structure that supports the vehicle’s weight and determines suspension geometry, a spring that converts kinematic energy to potential energy or vice versa, and a shock absorber that is a mechanical device designed to dissipate kinetic energy.

Function of suspension:

1)Support the weight of the frame, body, engine, transmission, drive train, passengers, and cargo.

2)Provide a smooth, comfortable ride by allowing the wheels and tires to move up and down with minimum movement of the vehicle.

3)Work with the steering system to help keep the wheels in correct alignment.

4)Keep the tires in firm contact with the road, even after striking bumps or holes in the road.

5)Allow rapid cornering without extreme body roll (vehicle leans to one side).

6)Allow the front wheels to turn from side to side for steering.

7)Prevent excessive body squat (body tilts down in rear) when accelerating or with heavy loads.

8)Prevent excessive body dive (body tilts down in the front) when braking.

The suspension systems are majorly grouped into two categories, which are as follows:


The nonindependent suspension has both left and right wheels attached to the same solid axle. When one tire hits a bump in the road, its upward movement causes a slight tilt in the other wheel. With a solid axle setup, the steering knuckle and wheel spindle assemblies are connected to the axle beam by bronze-bushed kingpins, or spindle bolts, which provide pivot points for each wheel.

INDEPENDENT SUSPENSION - The independent suspension allows one wheel to move up and down with a minimum effect on the other wheels. Since each wheel is attached to its own suspension unit, movement of one wheel does NOT cause direct movement of the wheel on the opposite  side of the vehicle.Many sports cars and some trucks and SUVs use an independent rear live axle

Various other types of Suspension Systems

Mac-Pherson Struts:

The popularity of small FWD vehicles has brought with it the dominate type of suspension system used today, the MacPherson strut suspension. These systems combine a coil spring, shock absorber, and bearing plate into a single unit.This arrangement allows for greater engine compartment space and reduced weight compared to short/long arm suspensions.The strut connects to the car body through the upper strut mount or bearing plate, which also acts as a pivot and damper.


Multilink systems are designed to produce neutral steering on FWD vehicles, which tend to exhibit understeer with traditional MacPherson strut suspensions. This suspension is also commonly used on RWD cars, light trucks, and SUVs. Multilink suspensions are also found on the rear of many vehicles, both FWD and RWD. Several control arms are used to reduce rear axle movements and provide better handling and ride qualities than a traditional rear strut system.

Short/Long Arm:

Short/long arm suspensions, also called SLA suspensions, are typically used on RWD vehicles. This suspension consists of two unequal length control arms connected with a steering knuckle. The control arms are generally triangular and are often called wishbones or A-arms. A steering knuckle, control arm bushings and ball joints comprise the rest of the suspension.


This suspension system was used on Ford trucks and vans for many years. Twin I-beams are strong and simple like solid axles but provide independent movement of the front suspension.I-beams are similar to very long control arms. They move on a pivot and allow for vertical wheel movement while the radius arm stops forward and backward movement of the suspension A large, straight I-beam is often used on the front of heavy-duty vehicles, such as buses and semi trucks.

Solid- Axles:

The solid axle that is physically connecting both wheels to the same housing, is what makes the suspension dependent. This means that regardless of the exact suspension type, one wheel moving up or down will directly impact the wheel on the other side.


A vehicle with a solid rear axle that does not drive the rear wheels has what is called a dead axle or a rigid or straight axle.A dead axle supports the weight of the rear of the vehicle and can be fitted with coil, leaf, or air springs. A dead axle is a dependent form of suspension.

Live Axles:

A live axle introduces a drive to a solid axle, with driveshafts being contained within the axle casing. With a differential being the centre point of the axle, the driveshafts protrude from either side and drive each wheel. Many heavy-duty 4WD trucks use a live front axle. This is because of the strength and durability of the axle. The live axle does not permit independent front wheel movement, so ride quality and handling suffer compared to a vehicle with an independent suspension. Typically, only the heavy-duty versions of a 4WD truck will have a live front axle because of this

Double Wishbone Suspension: The double wishbone suspension was first used in the 1930’s in Europe and then in 1935 in Detroit.The double wishbone suspension system consists of two equal‐sized short wishbone shaped members (arms) positioned one over the other. The closed ends of the two wishbone arms are hinge mounted to the top and bottom of the vehicle knuckle to provide vehicle steering. The vehicle knuckle supports the spindle or hub to which the wheel is mounted. The two open ends of each wishbone member are hinge‐mounted to the vehicle frame. In the event that the double wishbone suspension is used for a drive‐wheel application, a coil spring is seated on the central portion of the upper arm

Springs:The springs in the suspension have two important functions.

Springs support the vehicle weight and absorb the bumps and movements that occur when driving.

Types of springs:

Leaf springs: These are long semi-elliptical pieces of flattened steel and are used on the rear of many vehicles.Leaf springs are typically mounted as shown in Leaf springs have been in use since the horse-and-buggy days. A leaf spring is a long, flat piece of spring steel, shaped into a semicircle. The spring is attached to the frame through a shackle or bracket assembly that permits changes in the effective length of the spring as it is compressed.

Coil springs:

These are a length of steel wound into a coil shape. Used on most front and many rear suspensions, coil springs, are large pieces of round steel formed into a coil. The spring absorbs energy as the coils are forced closer together. This is called compression.The stored energy is released when the coil extends back out. The energy continues to dissipate as the spring bounces.

Air Springs:

These are thick, tough bags filled with air that act as springs. Air springs are used on some larger sedans and most large commercial semi trucks and trailers. Air springs are typically located in the rear, though some manufacturers use air springs at both the front and the rear

Torison Bar:

These are coil springs that are not coiled.Torsion bars are lengths of round steel bar fastened to a control arm on one end and the frame on the other end. Movement of the control arm causes the torsion bar to twist. The absorption of the twist is similar to compression of a coil spring. As the torsion bar untwists, the control arm returns to its normal position. Torsion bars are used in many 4WD vehicles where a front drive axle occupies the space where the coil spring normally sits.

Shock absorbers

Shock absorbers are actually dampers, meaning that they reduce or make something less intense. The springs do the shock absorbing while the shocks dampen the spring oscillations.The shock absorbers used in suspension system prevents the main frame from the shocks provided by the rough road conditions by absorbing the shocks which in turn makes the ride smooth for the passengers and the luggage.Without the shocks, our vehicles would continue to bounce for a long time after every bump, dip, and change in body movement

Electric suspension systems

Electronic suspension is essentially a computer-controlled system that can adjust the ride characteristics and performance of the vehicle.

There are two types of electronic suspensions: adaptive and active. Each one works in a different way to improve performance

Adaptive Electronic Suspensions

An adaptive electronic suspension is responsible for controlling the shock absorbers and their dampening performance. Simply put, they adjust the shocks as needed to deliver a smooth driving experience.Adaptive suspensions can adjust the shocks using a solenoid and valve that’s placed on the strut.The solenoid connects to a computer in the system and monitors the road conditions

Active Electronic Suspensions

An active electronic suspension changes the ride height for the vehicle to improve performance and towing capabilities. 

This type of electronic suspension uses hydraulics or electromagnets to operate.

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