1.

Introduction
The suspension system of off-road vehicles is a critical component that plays a pivotal role in
ensuring stability, control, and optimal performance in demanding off-road conditions. These
vehicles are subjected to extreme terrains, including sandy deserts, rocky trails, and high-speed
jumps, requiring robust suspension setups to withstand the challenges and deliver an exhilarating
off-road experience. Understanding the purpose of suspensions, the various types available, and
the process of selecting the appropriate system is essential for designing and building capable
off-road vehicles that can conquer these treacherous landscapes.
The primary purpose of suspension systems in off-road vehicles is to facilitate the smooth and
controlled movement of the vehicle's wheels while maintaining maximum contact with the
ground. By absorbing shocks and impacts encountered during off-road racing, suspensions
protect the vehicle and its occupants from excessive jolts, enhancing comfort and reducing the
risk of damage to vital components. Additionally, suspensions optimize tire contact with the
ground, ensuring superior traction and stability, which are paramount for maintaining control and
maneuverability in challenging terrains, sharp turns, and high-speed jumps.
Off-road vehicles employ various types of suspension systems, each offering unique
characteristics to suit different requirements. Independent suspension systems, for example,
allow each wheel to move independently, enhancing wheel articulation and improving traction
on uneven surfaces (Milliken & Milliken, 2002). On the other hand, solid axle suspensions,
commonly used in rear axle configurations, provide durability and strength, making them
suitable for tackling rough off-road conditions.
The selection of a suitable suspension system for off-road vehicles involves considering several
factors. These factors include the intended use of the vehicle, the nature of the terrain and
conditions to be encountered, the desired performance characteristics, and compliance with
specific regulations and class requirements in off-road racing events.
Out of these available designs, double wishbone type suspension is selected which gives
adequate space for wheel assembly, better control over design characteristic and flexibility to
designer in terms of performance variables.

1.1. Objectives of a Suspension System

It is important to analyze the suspension systems that have been designed to predict the
behavior of the system than followed with improvements. The suspension must be
properly designed because it is a crucial subsystem in vehicle in order for:

 Enhanced Off-Road Performance: The primary objective of the suspension

system in a Baja type off-road car is to enhance its performance in rugged
terrains. It should provide optimal traction, stability, and control to tackle
obstacles, bumps, and uneven surfaces encountered during off-road racing.
  Improved Wheel Articulation: The suspension system should allow for
maximum wheel articulation, enabling the wheels to maintain contact with the
ground even in extreme off-road conditions. This helps to ensure consistent
traction and maneuverability.

 Effective Shock Absorption: The suspension system should effectively absorb

shocks and impacts to protect the vehicle and its occupants from excessive
vibrations and jolts. It should provide a smooth and comfortable ride while
minimizing the transfer of forces to the chassis and other components.

 Durable and Reliable Design: The suspension system should be designed to

withstand the harsh conditions of off-road racing, including high-speed jumps,
rough terrains, and heavy impacts. It should be robust, durable, and resistant to
damage, ensuring longevity and minimizing maintenance requirements.

 Compatibility with Safety Equipment: The suspension system should be

compatible with the installation of safety equipment, such as roll cages and
harnesses, ensuring the safety of the driver and co-driver during off-road racing
events.

1.2. Need of Double Wishbone Suspension System

Off-road vehicles, particularly those designed for extreme terrains like Baja racing,
require suspension systems that can withstand the rigorous demands of off-road
conditions while providing optimal performance and control. Among the various
suspension designs available, the double wishbone suspension stands out as a popular and
effective choice for off-road enthusiasts and racing teams.

The need for a double wishbone suspension arises from its unique capabilities and
advantages. One key advantage is its ability to maintain consistent tire contact with the
ground. In off-road racing scenarios, where traction is crucial, the double wishbone
suspension excels by providing better control over wheel movements. Each control arm
acts as a separate link, allowing independent vertical movement of the wheel. This
reduces the impact of one wheel's movement on the others, resulting in improved traction
and better handling.

Another significant benefit of the double wishbone suspension is its ability to fine-tune
suspension geometry. The design allows for adjustments in parameters such as camber,
caster, and toe, which play a crucial role in optimizing tire alignment. By adjusting these
parameters, the suspension system can maximize tire contact area during cornering,
enhancing grip, and reducing tire wear.
 Moreover, the double wishbone suspension provides superior wheel control compared to
other suspension systems. Its inherent design allows for precise control over suspension
geometry, reducing body roll and enhancing stability during high-speed maneuvers and
off-road jumps. This translates to improved handling and responsiveness, enabling
drivers to push the limits of their vehicles with confidence.

1.3. Parameters affecting the Suspension performance

Camber:
Camber refers to the angle at which the wheels of a vehicle tilt inward or outward when
viewed from the front. It is measured as the inclination of the top of the tire relative to the
vertical axis. Positive camber occurs when the top of the tire leans outward, away from
the vehicle, while negative camber is when the top of the tire tilts inward, towards the
vehicle. Camber affects tire wear, cornering stability, and handling characteristics. The
camber angle is typically specified in degrees.

Caster:
Caster is the angle formed by a line passing through the upper and lower ball joints of the
steering knuckle and the vertical axis. It is measured when viewed from the side of the
vehicle. Positive caster is when the line tilts backward, towards the rear of the vehicle,
while negative caster is when the line tilts forward. Caster influences the vehicle's
straight-line stability, steering feel, and returnability after turns. It is typically specified in
degrees.

Toe:
Toe refers to the angle between the longitudinal axis of the vehicle and the direction of
the wheels when viewed from the top. It can be positive or negative, depending on
whether the wheels point inward or outward in relation to the vehicle's centerline. Toe
alignment affects tire wear, straight-line stability, and steering response. Toe is typically
measured in degrees.

Kingpin Inclination:
Kingpin inclination, also known as steering axis inclination (SAI), is the angle formed
between the steering axis and the vertical axis when viewed from the front of the vehicle.
It is determined by the inclination of the steering knuckle's pivot axis. Kingpin inclination
contributes to steering stability, self-centering, and reduced steering effort. The angle is
typically specified in degrees.
 Sr. PARAMETERS VALUES
NO.
1. Wheelbase
2. Track Width Front
Rear
3. Ground Clearance
4. KingPin Inclinition
5. Caster Angle
6. Camber Angle
7. Tire Front
Dimensions Rear

Table -1.1: Essential parameters related to suspension system

PARAMETER VALUES
Upper Length
Wishbone Angle
Lower Length
Wishbone Angle
Roll Center Height

Table -1.2: Final Geometry Parameter

2. Design Methodology

I. Defining Vehicle Specifications: We started by defining the specific

requirements and specifications of the vehicle's suspension system. This includes
factors such as vehicle weight, weight distribution, desired ride height, wheelbase,
track width, and suspension travel.
II. Gathering Suspension Geometry Data: We obtained the necessary suspension
geometry data, such as control arm lengths, angles, and mounting points. This
information was obtained from existing vehicle designs, reference materials, and
CAD models.
III. Creating a Model in Lotus Suspension Analysis (Lotus Software): We
imported the vehicle model into Lotus Suspension Analysis software. This was
done by creating a 3D CAD model and exporting it in a compatible file format
(e.g., IGES, STEP)
IV. Setting Up Suspension Parameters: We defined the suspension parameters
within the Lotus software, such as spring rates, damping characteristics, anti-roll
bar properties, and tire models.
V. Defining Boundary Conditions: the boundary conditions for the suspension
analysis were specified. This includes setting up the track conditions, tire loads,
and any external forces or inputs that the suspension system will encounter during
operation.
VI. Performing Static Analysis: We conducted a static analysis to evaluate the
suspension system's behavior under static conditions. This analysis helped us to
determine the vehicle's ride height, suspension deflection, and weight distribution.
Adjust suspension parameters as needed to achieve the desired static
characteristics.
VII. Optimizing Suspension Design: Based on the analysis results, we made design
modifications to optimize the suspension system's performance. This involved
adjusting suspension geometry, changing spring and damper rates

Obtain data from Lotus Software

Create CAD model in SOLIDWORKS

Evaluate design in ANSYS

Mechanical

Is the
design ok? Figure: Process Flow

Finalize the design

2.1. Designing Wishbone
Design of the suspension was administered in computer aided designing (CAD) using
SOLIDWORKS for designing purpose. Design of wishbones is that the necessary step to
construct a suspension system. Initially, for designing we’ve located coordinates from
Lotus.

Front Suspension
Front suspension, often known as short long arms (SLA), was achieved with a double
wishbone suspension system of uneven length and parallel. We usually decide on the
wishbone's final shape as an arm because it effectively and properly distributes stresses
among the members. Shorter than lower wishbone is upper wishbone. Having completely
different lengths has the advantage of increasing stability by inducing negative camber
after the vehicle flips.

Rear Suspension
In order to avoid any complexities considering the time constraints we decided to go for
the same parallel uneven length double wishbone suspension system for the rear of the
vehicle too. At rear side the camber angle and the toe angle can be zero. We'll mount the
spring within the higher stiffness which is able to be tilted towards the axle side.

2.2. Upright
Upright is designs in solidworks considering the dimensions of the tyres used. Upright is
designed with great care to ensure that it holds the upper and lower pivot points of the
control arms, the hub and the brake calipers without causing any sort of calamity

2.3. Material for Control Arms

When selecting materials for control arms in a wishbone suspension system, several key
considerations must be taken into account. The chosen materials should possess high
strength and stiffness to withstand the significant forces and loads experienced by control
arms. Other than that, this selection also depends on the availability and the cost
parameter. Considering all this we chose AISI 1018 for making control arms for our
suspension

Table 1.3: Properties of AISI 1018

3. Calculations
4. Analysis and Results
5. References
 Ackermann, J. (2014). Design and Analysis of Suspension System for an All-terrain
Vehicle. International Journal of Applied Engineering Research, 9(23), 19485-19491.

 Ashok, D., Sridharan, M., & Sugumaran, V. (2015). Design and Analysis of Double
Wishbone Suspension System for an All-Terrain Vehicle. International Journal of
Engineering Research & Technology, 4(07), 1093-1098.

 Bolourchi, S., Rahnejat, H., & Abu Bakar, R. (2018). Active Suspension Systems:
Design and Development. Journal of Physics: Conference Series, 1065(9), 092017.
doi:10.1088/1742-6596/1065/9/092017

 Bucholtz, A. (2018). Suspension Design: A Powerful Tool for Vehicle Dynamics.

SAE Technical Paper 2018-01-0568. doi:10.4271/2018-01-0568

 Esmailzadeh, E., Saed, S., & Mamaghani, I. (2018). Optimal Design of a Double
Wishbone Suspension System for an Electric Vehicle. International Journal of
Automotive Engineering, 9(3), 331-340. doi:10.22119/ijae.2018.53090

 Fujimoto, H., & Kokubo, S. (2014). Design of a Double Wishbone Suspension

System Considering Bump Steer and Camber Gain Characteristics. SAE International
Journal of Passenger Cars - Mechanical Systems, 7(2), 666-674. doi:10.4271/2014-
01-1983