Curve Resistance for Turning Vehicle:
Vehicles are steered by the turning of front wheel on horizontal curve, the direction of rotation of rear and front wheels are different, so direction of rotation of rear and front wheels are different, there is some loss in the tractive force. (Traction, or tractive force, is the force used to generate motion between a body and a tangential surface, through the use of dry friction, though the use of shear force of the surface is also commonly used.)
The tractive force given by the rear wheels is T and tractive force available in the direction of movement is T cos α.
Loss = T - T cos α
Therefore curve resistance means loss of traction force due to turning of vehicle on horizontal curve is, T - T cos α
More curve resistance is on the sharpe curve.
Grade Compensation:
When there is a horizontal curve in addition to gradient then there will be increased resistance to traction due to both curve and gradient, therefore it is necessary to compensate the gradient at horizontal curve.
IRC suggested to compensate the grade so that pulling power of vehicle cannot be compromise, therefore grade compensation taken is minimum of,
where,
R = radius of curve
Compensated Grade = Gradient - Grade Compensation
According to IRC grade compensation is not necessary for the gradient flatter than 4 %
