The study of the aerodynamics of road vehicles.
Its main goals are reducing drag and wind
noise, minimizing noise emission, and preventing
undesired lift forces.
Its also important to produce down-force to improve
traction and thus cornering abilities.
An aerodynamic automobile will integrate the wheel arcs
and lights into the overall shape to reduce drag.
MECHANICS OF AIR FLOW
AROUND A VEHICLE
In fluid mechanical terms, road vehicles are bluff bodies
in very close proximity to the ground.
Internal and recessed cavities which communicate freely
with the external flow and rotating wheels add to their
geometrical and fluid mechanical complexity.
The objectives of improvement of flow past vehicle bodies
are to reduce of fuel consumption and improve the driving
Vehicle aerodynamics includes three interacting flow
fields which are:
a. flow past vehicle body
b. flow past vehicle components (wheels, heat
exchanger, brakes or windshield)
c. flow in passenger compartment.
ON A VEHICLE
The pressure distribution over the body surface exerts
normal forces which, summed and projected into the freestream direction.
Combination of shock wave effects, vortex system
generation effects and wake viscous mechanisms
When the viscosity effect over the pressure distribution is
considered separately, the remaining drag force is called
pressure (or form) drag.
In the absence of viscosity, the pressure forces on the
vehicle cancel each other and, hence, the drag is zero.
The force exerted on a body whenever there is a relative
velocity between the body and the air.
There are only two basic sources of aerodynamic force:
a. the pressure distribution
b. the frictional shear stress distribution exerted by the
airflow on the body surface.
The distribution of pressure and shear stress represent a
distributed load over the surface.
Drag refers to forces acting opposite to the relative motion
of any substance moving in a fluid.
Lift acts perpendicular to the motion.
Drag sources - the skin friction between the molecules of
the air and the solid surface of the aircraft.
The skin friction is an interaction between a solid and a
gas, so the magnitude of the skin friction depends on
properties of both solid and gas.
The additional drag components caused by the generation
of lift is induced drag.
Occurs because the flow near the wing tips is distorted
span wise as a result of the pressure difference from the
top to the bottom of the wing.
Called induced drag because it has been "induced" by the
action of the tip vortices.
It is also called "drag due to lift" because it only occurs on
finite, lifting wings.
A motor vehicle bumper which comprises a shield and a
spoiler hinged between two positions of stable equilibrium
Namely a high position in which at least a part of the
spoiler projects from the shield and,
a low position in which the spoiler extends the shield
The spoiler is suitable for adopting a third position of
stable equilibrium, in which it is completely retracted
behind the shield.
A front spoiler (air dam) is positioned under or integrated
with the front bumper.
In racing, this spoiler is used to control the dynamics of
handling related to the air in front of the vehicle.
To improve the drag coefficient of the body of the vehicle
at speed, or to generate down-force.
In passenger vehicles, the focus shifts more to directing
the airflow into the engine bay for cooling purposes.
Air dam will keep the nose steady and pointed at the
ground in high speed driving.
DECK LID SPOILERS
The trunk lid or boot lid is the cover allows access to the
main storage or luggage compartment.
A spoiler’s function is to 'spoil' unfavorable air movement
across a body of a vehicle in motion.
Spoilers are used primarily on sedan-type race cars.
They act like barriers to air flow, in order to build up
higher air pressure in front of the spoiler.
WINDOW AND PILLAR
Pillars are the vertical or near vertical supports of an
automobile's window area or greenhouse-designated.
Which is A, B, C or D-pillar moving in profile view from
the front to rear.
Pillars are implied, whether they exist or not; where a
design's greenhouse features a break between windows or
doors without vertical support at that position
The non-existent pillar is "skipped" when naming the
A mass reduction enable fuel economy improvement.
Various global optimization methods use to solve drag
reduction problems in the automotive industry.
The genetic algorithms (GA) has the major advantage to
seek for a global minimum.
But this method is very time consuming because of the
large number of cost function evaluations that are needed.
All the hybrid optimization methods have greatly reducing
the time cost by coupling a GA.
In simple terms, density is the mass of anything including air - divided by the volume it occupies.
Lift and drag vary directly with the density of the air-as air
density increases, lift and drag increase.
As air density decreases, lift and drag decrease.
Air density is affected by pressure, temperature and
A common measure in automotive design as it pertains to
The drag coefficient of an automobile impact the way the
automobile passes through the surrounding air.
Aerodynamic drag increases with the square of speed;
therefore it becomes critically important at higher speeds.
Reduce drag coefficient to improves the performance of
the vehicle as it pertains to speed and fuel efficiency.
Cornering force is the lateral force produced by a vehicle
tire during cornering.
Its generated by tire slip and is proportional to slip angle
at low slip angles.
Slip angle describes the deformation of the tire contact
This deflection of the contact patch deforms the tire in a
fashion akin to a spring.
The deformation of the tire contact patch generates a
reaction force in the tire; the cornering force.
A fluid flowing past the surface of a body exerts a force
on it. Lift is the component of this force.
Lift is the force generated by propellers and wings to
propel aircraft and keep them in the air.
Lift can be in any direction since it is defined to the
direction of flow rather than to the direction of gravity.
When an aircraft is climbing, descending, or banking in a
turn the lift is tilted with respect to the vertical.
The moment (or torque) produced by the aerodynamic
force on the airfoil.
The pitching moment on the wing of an airplane is part of
the total moment that must be balanced.
The lift on an airfoil is a distributed force that can be said
to act at a point called the center of pressure.
If the moment is divided by the dynamic pressure, to
compute a pitching moment coefficient, this coefficient
changes only a little.
A yaw rotation is a movement around the yaw axis of a
vehicle that changes the direction the vehicle is facing.
The yaw rate or yaw velocity of a car or other rigid body
is the angular velocity of this rotation.
Yawing moment is the projection of a given torque over
the yaw axis.
It is important in road vehicles because pitch and roll
moments are limited by the floor reaction.
In a vehicle suspension, roll moment is the moment of
inertia of the vehicle's sprung mass.
Product of the sprung mass and the square of the distance
between the vehicle's roll center and its center of mass.
In aeronautics, the roll moment is the aerodynamic force
applied at a distance from an aircraft's center of mass.
A roll moment can be the result of wind gusts, control
surfaces such as ailerons, or simply by flying at an angle
The disturbances such as crosswinds should be minimized.
The increasing of this disturbances will make the driver
have difficulties in compensating it.
The sensitivity of a vehicle to cross-wind depends on
many factors involving the design of the suspensions and
the aerodynamics of the body.
Streamlined bodies with smooth transitions and paralleled
underbodies lead to low drag coefficients.
However, these measures cause the flow velocity around
the vehicle to increase.
This also increases the sensitivity of the vehicle’s oncentre handling under non-idealized flow conditions.
A method for estimating the aerodynamic loads on vehicle
due to crosswind on a road section is also presented.
The aim to find a relationship between steering feel and
Aerodynamic loads under real conditions were estimated
and the data were thereafter used in a study.
A term used to describe the energy generated by the
friction of a tyre rolling over a road surface
Tyre inflation pressure, tread compound, tread design and
temperature can affect the rolling resistance
The tyres are usually manufactured with a higher degree
of silica built into the compound
Silica allows the tyres grip performance to remain high,
especially in wet conditions, whilst rolling resistance is
A. TYRE TEMPERATURE
The temperature grades representing the tire's resistance to
heat generation and its ability to dissipate heat.
Tested under controlled conditions on a specified indoor
laboratory test wheel.
Sustained high temperature can cause the material of the
tire to degenerate and reduce tire life
While excessive temperature can lead to sudden tire
B. TYRE INFLATION
The level of air in the tire that provides it with loadcarrying capacity.
Affects the overall performance of the vehicle.
A number that indicates the amount of air pressure measured in pounds per square inch (psi).
Manufacturers of passenger vehicles and light trucks
determine this number based on the vehicle's design load
Rolling without slipping is a combination of translation
and rotation where the point of contact is instantaneously
When an object experiences pure translational motion, all
of its points move with the same velocity as the center of
The object will also move in a straight line in the absence
of a net external force.
D. TYRE MATERIAL AND
Tires provide a gripping surface for traction and serve as a
cushion for the wheels of a moving vehicle
Rubber is the main raw material used in manufacturing
tires, and both natural and synthetic rubber is used.
The other primary ingredient in tire rubber is carbon
In the tire design, the main features of a passenger car tire
are the tread, the body with sidewalls, and the beads.
E. TYRE SLIP
Slip is the relative motion between a tire and the road
surface it is moving on.
Can be generated either by the tire's rotational speed or by
the tire's plane of rotation being at an angle to its direction
In rail vehicle dynamics, this overall slip of the wheel
relative to the rail is called creepage.
Its distinguished from the local sliding velocity of surface
particles of wheel and rail, which is called micro-slip.
Tire Rolling Resistance Coefficient is calculated by
dividing the measured rolling resistance force
Comparing Rolling Resistance Coefficients only allows
comparing tires within a single size.
Larger tires generate higher Rolling Resistance Forces
than smaller tires.
Larger tires will often have a lower Rolling Resistance
Coefficient than smaller tires.
FUEL ECONOMY EFFECTS
Vehicle weight, aerodynamic drag, driving style and
rolling resistance can effect the amount of fuel.
Tyres can affect up to 1/3 of the vehicle's total fuel
consumption. Each tyre creates drag.
A vehicle's aerodynamics and its travelling speed have an
extremely large effect on how much fuel is consumed.
An environmental factors are impossible to control but
have a direct effect on fuel consumption.