1. Resistance to Vehicle Motion

2. Resistance to Vehicle Motion
Resistance is defined as the force impeding vehicle motion
What is this force?
Air or Wind resistance
Rolling resistance
Gradient resistance

3. Air Resistance Ra Air offers resistance to the movement of bodies
Resistance depends upon the size and shape of the body
Air resistance is caused by air pushing aside
Low vehicle speed- air resistance insignificant
Higher speed – air resistance predominant

4. Air Resistance Ra Composed of:
Turbulent air flow around vehicle body (85%)
Friction of air over vehicle body (12%)
Vehicle component resistance, from radiators and air vents (3%)
Power is in ft-lb/sec
from National Research Council Canada

5. Air Resistance Ra

6. Air Resistance Ra Influencing Factors Frontal area of the vehicle
Vehicle speed
Shape and streamlining body
Wind speed and direction

7. Rolling Resistance Rrl
Primary Cause
Resistance forces caused by the deformation of tyres, road surfaces and total weight of the vehicle including load
Secondary Cause
Wheel bearing, oil seal friction and churning
( undesirable friction) of the oil in the transmission system

8. Rolling Resistance Rrl

9. Rolling Resistance Rrl
Composed primarily of
Resistance from tire deformation (90%)
Tire penetration and surface compression ( 4%)
Tire slippage and air circulation around wheel ( 6%)
Wide range of factors affect total rolling resistance
Rolling resistance = 2 components
Hysteresis = energy loss due to deformation of the tire
Adhesion = bonding between tire and roadway

10. Rolling Resistance Rrl
Influencing Factors
Laden weight of the vehicle
Type of road surface
Design, construction and materials used in the manufacture of the tyre

11. Gradient Resistance Rg
Resistance experienced by vehicle when moving upward on a gradient or hilly road
Vehicle moving upward on gradient
Vehicle weight ‘W’ acting vertically downwards

12. Gradient Resistance Rg
Weight ‘W’ can be resolved into horizontal (H) and vertical (V) components
To prevent the vehicle to move backwards a force equal and opposite to ‘H’ must be applied
‘H’ is the resistance to the gradient
It depends on the steepness of the gradient (angle Ѳ) and the weight of the vehicle

13. Gradient Resistance Rg
Composed of
Gravitational force acting on the vehicle θg
For small angles, Rg θg W

14. Total Resistance It is the sum of the three resistances
Rolling and gradient resistances are independent of speed
Air resistance is dependent on speed

15. Total Resistance Speed OD km/hr
Total resistance AD= Air resistance (AB) Gradient resistance (BC) Rolling resistance (CD)