International Journal of Mechanical Engineering and Technology (IJMET)

Volume 8, Issue 6, June 2017, pp. 85–95, Article ID: IJMET_08_06_009

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=6
ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

SUSPENSION SYSTEM FOR AN ALL TERRAIN

VEHICLE
Kancharana Sunil
B Tech, Department of Mechanical Engineering,
Sreenidhi Institute of Science and Technology, India

J Kranthi Kiran
B Tech, Department of Mechanical Engineering,
Sreenidhi Institute of Science and Technology, India

ABSTRACT
The main objective of this paper is to explain the design methodology which has
been opted for the suspension system of an All Terrain Vehicle .Double wishbone
independent suspension system is designed for the front half and trailing arm
independent suspension is designed for the rear half. All the calculations which are
required have been discussed. The analysis of the suspension system is also done by
using simulation software Lotus shark.
Key words: Suspension system; All terrain vehicle; ATV.
Cite this Article: Kancharana Sunil and J Kranthi Kiran. Suspension System for an
All Terrain Vehicle. International Journal of Mechanical Engineering and
Technology, 8(6), 2017, pp. 85–95.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=6

1. INTRODUCTION
There are different types of suspension system which can be used for a vehicle depending
upon our need. Basically suspension can be classified into 2 types:
 Independent suspension
 Dependent suspension
1) Independent Suspension : The term independent indicates that suspension system for both
the wheels are independent of one another i.e., whenever a bump or droop comes across ,both
the wheels behave independently. To put it up in simple terms the wheel travel ( movement of
wheel up and down in vertical direction) can be seen only on that side where the wheel
undergoes bump or droop. Where as the other wheel maintains contact with the road.
Examples of independent suspension :
i) Double wishbone
ii) Mc person struct
iii) Swing arm

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 Suspension System for an All Terrain Vehicle

2) Dependent Suspension : In this type suspension if one wheel undergoes a wheel travel
due to bump or droop the opposite wheel also undergoes the wheel travel, Unlike the
independent suspension.
Example of dependent suspension :
i) leaf spring
ii) live axle
For an all terrain vehicle where the vehicle is made to run at different uneven terrains it is
always better to opt for independent suspension system rather than dependent suspension. Of
all the independent suspension systems available by studying the merits and demerits of each
and every type, double wishbone and trailing arm suspension have been preferred for front
and rear respectively.
The main functions of the suspension system in vehicle are:
i) To maintain traction between the tires and ground
ii) To improve vehicle handling
iii) To provide a ride comfort to the passengers

2. CALCULATIONS
Total sprung mass: The entire mass that acts upon the wheels of the vehicle is considered as
sprung mass i.e weight of the roll cage ,driver, engine, cvt, steering wheel, steering rack,
braking. The lower the sprung mass is the better the performance of the vehicle.
Sprung mass:175 kgs
Total unsprung mass: The mass excluding the sprung mass is considered as unsprung mass
i,e weight of the wheels, uprights, knuckles, a arms, Hubs, shock absorbers, trailing arms.
Unsprung mass: 65 kgs
Total weight: sprung mass + unsprung mass gives the total weight of the vehicle
Total weight:175 +65 = 240kgs
Kerb weight: The weight of the vehicle excluding the driver’s weight
(Also known as curb weight)
Kerb weight : 240 – 60 = 180kgs
(Drivers weight is considered as 60kgs)
Front track width: Front Track width is the distance from tire centre to the other tire center.
There is no specific formulation in deciding the track width of the vehicle but we need to
consider certain basics like[1]
1) up to what value the rules will allow ?
2) what is the predominant track type the on which vehicle is to be run?
3) Are low speed tight circuits are of concerns ?
4) Is top speed thus top frontal area is important ?
Front track width: 52’’inches
Rear trackwidth: selection criteria for rear track width depends upon the same
considerations as of front. However, we preferred the rear track width to be slightly greater
than front for more stability of the vehicle
Rear track width :53’’inches

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 Kancharana Sunil and J Kranthi Kiran

Static Ride height: static ride height is also said to be ground clearance. It is nothing but the
distance between the ground to the chassis lowest point . It is always desirable to maintain a
ride height at a moderate height which is not too high and not too low because if the ride
height is low the vehicle may get hit at the bottom during getting over a bump and if the ride
height is very high the height of COG increase which is also not a desirable scenario. So by
benchmarking the ride heights of different commercial ATV’s the ride height for our vehicle
is determined as
Static ride height :12’’inches
Tire diameter: The selection criteria for the diameter of the tire depends upon 2 factors
1) Vehicle torque
2) Braking disc and caliper that gets fitted inside rim
Tire diameter: 23”inch
Wheel travel: The movement of the wheel in vertical direction from top to bottom is known
as wheel travel.

Table 1 The wheel travel of several vehicles is listed below[2]:

Type of car Wheel travel
Off road +/- 12
Passenger +/- 4
Formula and +/- 2 to 4
sports cars
Indy type +/- 0.5
So based upon the above data available the wheel travel for the front and rear has been
considered as:
Wheel travel front: 10 inches (4 inch bump,6 inch droop)
Wheel travel rear: rear wheel travel is intentionally chosen to be less because if it is
increased then there may arise a problem of slippage of split transmission shafts from the gear
box which is connected to the rear wheel.
Wheel travel rear : 6 inches (4 inch bump,2 inch droop)
Spring travel: The maximum length that the spring can compress under the application of a
certain load is known as spring travel.
Front spring travel: Fox Float 3 evol R shock absorbers are used for the front suspension
whose maximum spring is restricted to 5.3 inches[3].
Front spring travel : 5.3 inches
Rear spring travel: for rear whose wheel travel is low when compared to front the spring Is
also has been reduced and customized shock absorbers have been used whose spring travel is
3 inches.
Rear spring travel :3”inches
Installation ratio: the installation ratio is also known as motion ratio which is determined as
spring travel/wheel travel.
Front: 5.3”/10”=0.53
Rear: 3”/6”=0.5
Ride frequency: it can be considered as the undamped frequency of the body moving up and
down on the springs. usually the ride frequency can be determined once the static deflection
has been estimated.

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 Suspension System for an All Terrain Vehicle

Figure 1 Graph represents relation between ride frequency and static deflection [4]

Table 2 Ride frequency for few cars has been studied as [5]:
Type of car Ride frequency
Sports car 70-90 cpm
Indy car 95-120 cpm
Passenger car 30-50 cpm
Higher the ride frequency, Stiffer the ride gets and vice versa. Usually ride Frequency of
the rear is chosen more than that of the front in order to stabilize the Vehicle as soon as it hits
a bump. When ever the vehicle comes across a bump the Front wheels undergoes vibration
and after a time lapse the rear wheels vibrate. So if the ride frequency for rear is chosen more
so that both the wheels will stabilize at same time

Figure 2 Normal case graph amplitude vs time [6]:

Figure 3 graph when 10% rear ride frequency is increased [7]:

The ride frequency for front : 2 hz and for rear: 2.5 hz

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 Kancharana Sunil and J Kranthi Kiran

Spring constant: It is defined as force applied for unit deflection of spring. It is also defined
as spring stiffness. The S.I. units for spring constant are N/mm or N/m. One of the key
parameter of the suspension system. Generally spring constant(k) = force X displacement.
But in the automobiles undergo continuous fatigue loading, so due to this reason instead
of normal formula we make use of ride frequency and obtain the spring constant value.
We know that
w = √ (k/m)
where w = amplitude
k = spring constant
m= sprung mass
we also knew that
w= 2πf
where f = ride frequency
on equating both the equations we get
k = 4π2mf2
units :N/m
using the above formula the spring constants for the front and rear suspension system are
calculated . Quarter body analysis of the sprung mass is done so that sprung mass acting on
each wheel is determined
The weight distribution according to the calculation is front : rear = 42.5:57.5
Front spring constant:
Entire sprung mass = 175 kgs
Front sprung mass = 175 x 0.425 = 74.375kgs
Multiplying the above mass with factor of safety : 74.375 x 1.5=111.5625 kgs
The load acting on each wheel at front : 111.5625/2 =55.8 kgs
k = 4π2mf2
k = 4 x π2 x 55.8 x 22
k = 8811.58 N/m or 8.81N/mm
For front suspension FOX float 3 evol R pneumatic shock absorbers which have
adjustable spring rate have been used.
Rear spring constant:
Entire sprung mass = 175 kgs
Rear sprung mass = 175 x 0.575 = 100.625 kgs
Multiplying the above mass with factor of safety : 100.625 x 1.5=150.93 kgs
The load acting on each wheel at front : 150.93/2 =75.46kgs
k = 4π2mf2
k = 4 x π2 x 75.46 x 2.52
k = 18619 N/m or 18.619N/mm
For rear suspension customized shock absorbers have been used
Spring calculations :
k = Gd4 /8D3N [8]
Where k= spring constant

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 Suspension System for an All Terrain Vehicle

G= modulus of rigidity= 81370 N/mm2

d= wire diameter
D= mean diameter
N= No. of active turns
C = D/d =spring index
Assuming C= 8 and N =12
k = Gd4 /8D3N
18.619 = 81370 x d4 /8 x (8 x d )3x12
d = 11.2 = 11mm approximately
D = C x d = 8 x 11 = 88mm
Wheel rate: vertical force per unit vertical displacement at the location along the spindle
corresponding to the wheel center line measured relative to the chassis.
Wheel rate = spring rate x (motion ratio)2[9]
Front wheel rate = 8.81 x (0.53) = 2.474 N/mm
Rear wheel rate = 18.619 x (0.5)2 =4.654 N/mm
Roll center height: Roll center height plays an prominent role in suspension Whenever the
vehicle undergoes rolling it is said to be rolled around an axis called roll axis. This roll axis is
a line that passes through the 2 points called roll centers. During cornering of the vehicle there
acts a centrifugal force an outgoing pseudo force on the vehicle which results in moment arm .
This moment arm depends upon the centrifugal force and the distance between the roll center
and COG so if the distance between roll center and COG increases then the moment arm
produced will have a high value which results in the rolling of the vehicle. thus it is
mandatory that the distance between roll center and COG should be kept as small as possible.
Roll center height is found by

Figure 4 Roll center calculation

Front roll center height from ground: 167.39mm
Rear roll center height from ground : 177.818mm

3. LOTUS ANALYSIS
Lotus shark [10] is a Market Leading Application For Suspension Modeling And Design.
From The World-Leaders In Vehicle Ride And Handling; The Lotus Suspension Analysis
Shark Module Is A Suspension Geometric And Kinematic Modeling Tool, With A User-
Friendly Interface Which Makes It Easy To Apply Changes To Proposed Geometry And
Instantaneously Assess Their Impact Through Graphical Results.

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 Kancharana Sunil and J Kranthi Kiran

The virtual representation of the suspension system can be designed using this software all
the mounting points can be changed according to our desire .once every input is given the
simulation can be performed and various number of graphs (upto 18 different) can be
obtained. The graphs include camber change vs wheel travel , wheel travel vs toe angle
change , wheel travel vs Ackermann percentage , camber vs castor and so on. Once these
graph are obtained they are given a detailed study and changes are made if they are required ,
if not the hard points (mounting points ) are obtained which are used as reference during
manufacturing phase.

Figure 5 Simulation of the vehicle suspension in Lotus shark software:

Camber is defined as tilting of wheel inwards or outwards when viewed from the front
view. If the top of the wheel is tilting inside and bottom of the wheel is tilted out , it is said to
be negative camber . negative camber is Denoted by – sign. If the bottom of the wheel is tilted
inside and the top is tilted inside , it is said to be positive camber denoted by + sign. If the
wheel is perfectly straight without any tilt it is said to be zero camber.

Figure 6 Pictorial Representation of camber [11]

Zero camber is desirable always because it maintains a uniform contact patch with the
ground. But however zero camber cannot be achieved due to the irregularities on the road.
The following graph is called as camber curve which discusses about camber change with
wheel travel. It tells that the front wheels will undergo some camber which is appreciably
small and there is no camber change for rear wheels.

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 Suspension System for an All Terrain Vehicle

Figure 7Camber curve

4. HARD POINT PICK UP

The Hard point pickup is nothing but the mounting points to of the suspension system for the
chassis. After doing several iterations and lotus suspension stimulation software we decided
the above hard points while deciding the we studied the following properties in three different
types of motion
 3 Dimensional bump
 3 Dimensional steer
 3 Dimensional roll
Inputs:
 Front: 6” bump, 4” droop Rear: 4”bump, 2”droop
 Roll: 2 degree

Dimensional Steer with 40mm rack travel

Table 3 Hard points for double wish bone
Front X (mm) Y (mm) Z(mm)
Lower 329.4 205.5 334.876
Wishbone
front pivot
Lower 467.45 203.5 310.339
Wishbone
rear pivot
Lower 348.4 551.5 217.1
Wishbone
outer ball
Joint
Upper 204.33 205.5 367.1
Wishbone
front pivot
Upper 500.0 205.5 367.1
Wishbone
rear pivot
Upper 426.6 525 260.3
Wishbone
outer ball
Joint
Damper 398.4 380.7 632.7

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 Kancharana Sunil and J Kranthi Kiran

Wishbone
End
Damper 462.11 205.5 292.1
body end

Outer track 525.15 493.9 378.8

rod ball joint

inner track 590.15 205.5 260.3

rod ball joint

Wheel 414.25 531.5 295.3

spindle point

Wheel 411.35 660.4 292.1

center point

Table 4 Hard points for trailing arm

Rear X(mm) Y(mm) Z(mm)
Trailing 2891 410 207
Arm
front pivot
Lower 3625 126 190.5
Link inner
Ball joint
Lower 3492 595.5 166
Link
outer ball
Joint
Upper 3604 185 424
Link inner
Ball joint
Upper 3491 630 423
Link outer
Ball joint
Damper lower 3654 595 166
Trailing arm
End

Damper 3450 300 600

Body
End
Upper spring 3450 300 600
Pivot end

Spring lower 3494 595 166

Trailing arm end

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 Suspension System for an All Terrain Vehicle

5. CONCLUSIONS

Figure 8 Front suspension

Figure 9 Rear suspension

Figure 10 Fabricated All Terrain Vehicle

Figure 11 Completely fabricated vehicle during testing.

By using the above calculations and design methodology the suspension system for an all
terrain vehicle i.e., double wish bone suspension for front and trailing arm for the rear has
been fabricated successfully. The vehicle has been tested at different terrains in order to test
it’s handling , traction and suspension efficiency and In all cases it has worked efficiently.

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 Kancharana Sunil and J Kranthi Kiran

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