dear pawan,
The spokes to the cycle wheel increases the moment of inertia due to the increase in thedistribution of mass. This opposes the change in the rotary motion of the wheel. Thus spokes fitted to the cycle wheel gives a steady motion.
						

							The spokes if cycle wheel increases it`s moment if inertia.the greater is the momentum of inertia,the more is the opposition to any change from other external forces in it from the uniform rotational motion.as a result cycle moves smoothly and steadily
						

							They creat suitable aerodynamic torque so gravity is unable to put it downThat is the main reasonFor why spoke are provided in cycle
						

							
DEAR PAVAN,SPOKES ARE PROVIDED TO A BICYCLE WHELL BECAUSE TO ENSURE UNIFORM MOTION OF THE BICYCLE AND TO CONNECT THE RIM TO THE CENTER 
HERE IW=CONSTANT BUT WE KNOW  I=MR2 AS RADIUS IS DIRECTLY PROPOTIONAL TO MOMENT OF INERTIA THIS GIVES A STEADY  ROTATIONAL MOTION
						

							To ensure uniform speed of cycle wheel, it should posses large moment of inertia. To increase moment of inertia of the wheel without large increase in its mass  it is provided with spokes.