What is Coning of Wheels in Railways ?

The flanges of the wheels of railways are made in the slope of 1 in 20. This is termed as Coning of wheels.

The tread of the wheels of a railway vehicle are not made flat, but sloped like a cone in order to enable these vehicles to move smoothly on curves as well as on linear straight track. The wheels generally remain central on a straight and level surface with uniform gauge and the circumference of the treads of both the vehicles are equal as can be seen in the figure.
The problem, however, arises in case of a curve, when the outer wheel has to negotiate more distance on a curve compared to the inner wheel. Due to centrifugal force, the vehicle on a curve tends to move out and the circumference of the tread of outer wheel thus becomes greater than that of the inner wheel. This helps the outer wheel to travel longer than the inner wheel.
The wheels of railway vehicles are connected by axles, which in turn is fixed on a rigid frame. Due to rigidity of the frame, the rear axles has a tendency to move towards the inner rail and this does not permit the leading axle to take full advantage of the coning. The rigidity of frame, however helps to bring the vehicle back in central position and thus works as a balancing factor.

On a straight and level track also the coning of wheels help to keep the vehicle in central position. Due to thrust of moving loads and vagaries of weather, slight irregularities in track do occur. The wheels, therefore move from side to side and swaying of vehicles take place. Due to coning of wheels, the side movement results in tread circumference of one wheel increasing than the other.
As both the wheels have to traverse the same distance, this leads one wheel to slide. Due to resistance of the sliding, further side movement is stopped. If the coning was not there, the side movement would have continued and the flange of the wheel would have come in contact with the side of the rail causing jerk and uncomfortable riding.

Coning of wheels causes wear and tear due to slipping action. However there are also some advantages of it :

• It helps the Vehicle to negotiate a curve smoothly.
• It gives smooth riding.
• It reduces the wear and tear of wheel flanges.

As far as slip is concerned, it can be mathematically calculates and it’s value is given by the formula.
$slip=\frac{2\pi \theta }{360}\times G$
The approximate value of slip for broad gauge comes to 0.029 meter per degree curve.