3.8
Factor Affecting Under Steering & Over Steering:
Tyre
cornering stiffness, speed of vehicle, camber thrust, lateral force compliance
steer, self-aligning torque, lateral weight transfer, and compliance in the
steering system or geometry like camber, caster, toe-in & toe-out. Change
in king pin inclination. Vehicle is going straight and is subjected to side
force to road camber or some cross wind.
Cornering stiffness of a tyre is its ability to resist deformation in the shape of a tyre while the vehicle corners. The more flexible the tyre is the less stiffer it is. When a vehicle is moving at high speed, lateral force acting on tyres increases the possibility for vehicle to get into a critical situation. During the cornering, when tyre must develop a lateral force, tyre will also experience lateral slip as it rolls.
The
angle between the direction of heading and direction of travel is known as a
slip angle α. The
angle between direction of the motion of the vehicle and the center plane of
the tyre is known as Slip Angle. It ranges from 8º to 10º.
Cornering stiffness of a tyre is its ability to resist deformation in the shape of a tyre while the vehicle corners. The more flexible the tyre is the less stiffer it is. When a vehicle is moving at high speed, lateral force acting on tyres increases the possibility for vehicle to get into a critical situation. During the cornering, when tyre must develop a lateral force, tyre will also experience lateral slip as it rolls.
 |
| Fig 1: Slip angle |
The
cornering stiffness depends on many variables - tyre size and type (radial or
bias ply construction), number of plies, cord angles, tyre width and tread are
significant factors. The load and inflation pressure are the main factors affecting the
cornering stiffness. Speed
does not strongly influence the cornering forces produced by a tyre. A
Typical value for the cornering stiffness per degree of slip angle is
approximately 16-17% of the load on the tyre.
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