SUPERNOVA RACING

SUSPENSION
INTRODUCTION:
Suspension system for a racing car must be designed considering
various technical parameters in several fields. Our design covers the above discipline
and it also ensures the easy car handling and comfortable ride. This design governs
the issues due to the sprung and unsprung masses. Any particular geometry must be
designed to meet the needs of particular vehicle for which is to be applied. In order
the optimize the suspension geometry one requires the complete kinematics and
dynamics of suspense. In older days prediction of the various parameters and
suspension action is a complex process which have been simplified nowadays by
computational softwares like ADAMS and LOTUS.

FUNCTIONS:
 Suspension systems serve a dual purpose-contributing to vehicles road
handling and braking for good active safety and driving pleasure.

 It is important for a suspension to keep the road wheel in contact with the road
surface as much as possible.

 This system avoids the rolling of car while cornering suddenly or taking a
narrow turn.

 It withstands the weight displaced due to braking and also helps comfortable
steering at high speeds.

DESIGN METHOLOGY:
There are various design for suspension systems such as double
wish-bone, push rod , pull rod suspension etc. On considering various parameters like
roll centre ,centre of gravity ,motion rate we have decided to use a push rod
suspension system.

In a typical torsion bar pushrod set up described below the

torsion bars pass through the centre of the rockers and fix to the front of the chassis.
The rocker pivots on the torsion bar. The push rod pushed the rocker and twists the
torsion bar to provide the spring in the suspension ,the rocker then compress the
damper and operates the antiroll bar if the car is in roll.

Type of suspension Advantages Disadvantages

Push rod 1. better load angle to the 1. higher centre of gravity.
horizontal.
2. maintain car at same
level.

Pull rod 1. easy to mount heavy unit. 1. higher load on upper control
2. lower centre of gravity arm
2.aero disadvantage

Push rod suspension has an aero advantage over its pull rod counter
part.
It helps to channel the air properly towards the sidepods and the diffuser.

IMAGE OF ENTIRE SUSPENSION

Main parameters of suspension
Name Front Suspension Rear Suspension
Offset frequencies/Hz
Roll centre height/mm
Push rod length/mm
Free length of damper/mm
Castor angle
Camber angle
Toe angle

SPRING AND DAMPER:

The most common type of spring is the helical coil spring. when
compressed the reaction force is developed opposite of the applied force and tries to
bring the compressed spring back to its original state. The amplitude of vibration is
larger near resonance . In order to limit vibration dampers are used.

IMAGE
SPECIFICATIONS
ROCKER ARM:
A Rocker is a part of suspension system where bump force is translated
from push rod into the damper and ARB by changing a linear motion of an angle. The
relationship between the spring travel and travel is called motion ratio.
Supra rule for 2015 required car must have 1inch(25.4mm)
bounce and 1 inch (25.4mm) jounce with drivers seated inside the vehicle.

Motion ratio= Suspension travel/wheel travel

There are slight differences between motion ratio front

and rear rocker. As the unsprung mass is high in the rear the motion ratio is large in
the front.

Front Rear
Suspension travel
Wheel travel
Ratio

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SPECIFICATIONS

Material used for rocker is T6-6016 aluminium alloy. The material

specification is given in appendix.

PUSH ROD:
It transfers the force from vertical wheel travel to damper and spring
components. For push rod the rod reacts to the force as a compression member for a
car to maintain to contact with the ground while the A-arm that push rod attaches to is
reacting as a tension member.

LOAD THROUGH PUSH ROD:

Push road is generally chosen for better load angle. Load angle is
much more important than loosing a few milli seconds in corners and straight line
aerodynamic drag. Loading on push rod is a function of its angle meaning that force
will be applied to the wheel load

Fpushrod= FN/sin(ANGLE)

Push rod connection point is not located at the tip of the A-arm. Here a XXmm
distance is used to calculate the actual pushrod force.
Fpushrod actual= (Fpushrod*(30+x))/x
Where;
 x-dist from push rod connection point to the chassis
Normal Angle(o) Push rod Actual
force(N) force(N) force(N)
Front
Rear

INAGE+ SPECIFICATIONS+ REASON WHY ANGLE IS MADE AS

x

A-ARM:
A-arm or double wishbone-arm is one of the most important
suspension components of a race car. A-arm helps transferring the load from the
tires into the chassis, depending on the geometry.
A-arm suspension is designed by connecting the upright to the chassis of the car. The
connection links in a pair with shape of a letter A or wishbone. Control arm or A-arm
is composed of two steel pipes welded by a design angle, there is a short small
diameter steel tube in which the arms are welded At the end of the link there is
different type of bearings, which act as a suspension pivot point . The bearings that
were used for this car are rod ends connected to the chassis side and radial spherical
plain bearing connected to the upright

The length of different a-arms varies. Due to the fact that the chassis is wider at the
middle section than the lower section, this allows the upper a-arm to be shorter than
the lower ones.
FRONT REAR
UPPER LOWER UPPER LOWER
Length(f,r)
Angle b/w arms
Angle to the ground

IMAGE

A-arms are mirroring each other at left and right side of the car.
Length of each a-arm has been design to give 1240 mm front and 1200 mm rear
wheelbase. Angle of front a-arms is limited due to conflicting with steering arm when
the front wheels are turning. Angle of rear a-arms is limited due to length of the
chassis and sidepods location. At the rear wheels the horizontal angles are limited
due to large electric motor casing blocking the way. Material used for a-arm is
chromoly due to better mechanical properties than mild steel, see Appendix A.1 for
material properties

ANTI-ROLL BAR:
The anti-roll bar is a crucial part of the suspension system. The ARB
is a torsional rod designed to resist the body roll during lateral acceleration. The
concept of the ARB is to transfer some of the vertical forces from the outer wheel
during the corner to inner wheels. Load transfer helps inner wheels to stick to the
ground and keep the vehicle parallel to the surface . Both front and rear ARB are
located on top of the chassis .
IMAGE-SPECIFICATIONS