Coning of Wheels Explains Different Distances on Curves

Railway wheels are mounted on a single axle, forming a monolithic unit. This means both wheels rotate together at the same speed and complete the same number of revolutions simultaneously.

However, when a train navigates a curve, the outer rail is longer than the inner rail. If the wheels were purely cylindrical, they would attempt to cover the same distance (circumference) on both rails for each revolution. This would cause slipping between the wheels and the rails, especially on the inner rail, leading to wear and tear, noise, and instability.

Why Coning of Wheels is Essential on Railway Curves

The problem of covering different distances on a curve for the same number of revolutions is solved by a design feature called coning of wheels.

• Coning involves manufacturing the treads of the wheels with a slight taper. The diameter is larger towards the flange side (inner side) and smaller towards the outer side.
• On a straight track, the wheels are centered, and the effective diameter touching the rail is the same for both wheels.
• When the train enters a curve, centrifugal force tends to push the train outwards. This lateral movement causes the inner wheel to move towards the inner rail (where the diameter is smaller) and the outer wheel to move towards the outer rail (where the diameter is larger).
• As the outer wheel runs on a larger diameter and the inner wheel runs on a smaller diameter, the effective circumference for each wheel becomes different.
• For the same number of revolutions, the outer wheel, running on a larger diameter, covers a greater distance, while the inner wheel, running on a smaller diameter, covers a shorter distance.
• This difference in distance covered naturally matches the different lengths of the outer and inner rails on the curve, allowing the train to negotiate the curve smoothly without excessive slipping.

Understanding Other Options

While other options are related to railway track design, they do not directly explain why wheels cover different distances for the same revolutions:

• Widening of gauge: This is done on curves to provide clearance and reduce flange friction, but it doesn't change the fundamental mechanics of how wheels cover distance per revolution.
• Tilting of rails: Rails are tilted inwards (cant) to match the coning of wheels and help distribute the load evenly across the wheel tread, reducing wear and tear. It is related to coning but isn't the direct cause of different distances covered per revolution.
• Adzing of sleepers: Adzing is shaping sleepers to provide a proper seat for the rails and ensure the correct tilt of the rails. It's a track preparation process, not related to wheel mechanics on a curve.

Therefore, the phenomenon where outer and inner wheels cover different distances on a curve for the same number of revolutions is directly attributed to the coning of wheels.