The wheel is the most fundamental component of railway vehicles. It not only has to withstand vertical and lateral dynamic forces and friction between the wheel and rail, but also has to endure the thermal load during braking on the tread. It functions to bear weight, guide movement, transmit braking force, and provide traction. The operating conditions are extremely harsh, often resulting in damage such as wear, peeling, chipping, thermal cracking, and fatigue failure. The performance of the wheel has a significant impact on the safety of train operations.
The wheel structure is entirely determined by the wheel diameter, rim and hub dimensions, flange-to-rim distance, spoke shape, and the profile of the flange tread. Each dimension or part of the shape has its special significance.
The wheel diameter has a considerable impact on both the wheel itself and the entire vehicle. On one hand, the larger the wheel diameter, the higher the vehicle’s center of gravity, and the worse the vehicle's dynamic performance. On the other hand, increasing the wheel diameter can reduce the contact stress between the wheel and rail, decrease the rate of wheel wear, increase the wheel's thermal capacity, and improve its ability to withstand thermal loads during braking. Therefore, the wheel diameter should be determined comprehensively according to the vehicle's condition.
In general, the greater the axle load of the vehicle, the larger the wheel diameter should be to improve the wheel’s thermal capacity and increase the wheel-rail contact area, thereby reducing tread damage and wear. Additionally, the selection of wheel diameter should take into account standardization and serialization to facilitate wheel manufacturing and maintenance. Currently, the wheel diameter for China’s railway freight cars is mostly 840mm, while special freight car wheels have a diameter of 915mm.
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