Train wheel definition

The bogie is a component of a train, commonly referred to as the train wheels by the general public. When observing train wheels, one will notice many intricate components mounted on them. These components, when assembled with the wheels, form a complete unit known as the bogie.The bogie is a component of a train, commonly referred to as the train wheels by the general public. When observing train wheels, one will notice many intricate components mounted on them. These components, when assembled with the wheels, form a complete unit known as the bogie.

The emergence of train bogies

The emergence of train bogies greatly facilitated steering. In the early days, railway vehicles, commonly referred to as train carriages, were mostly two-axle cars. The wheelsets (train wheels) were directly mounted on the car body, unable to rotate relative to the body, making steering inflexible and causing significant wear on both the train wheelsets and the tracks. This setup even posed challenges in navigating certain curves. To enable carriages to smoothly navigate curves, especially those with smaller radii, carriages were kept relatively short (generally no more than 10 meters) to ensure passage through smaller radius curves. 

However, the inability of train wheelsets to rotate relative to the body made it difficult to increase the number of axles to enhance the carriage's load-bearing capacity (for two-axle cars). Although vehicles with three axles were introduced, they required a larger minimum curve radius, and the middle wheel had to move a certain distance relative to the curve radius (along the radius), increasing the complexity of the vehicle, especially with more axles. As railway development progressed and the demand for higher load capacities increased, adding more axles imposed stricter requirements on curve radii and vehicle complexity. Consequently, this type of vehicle gradually phased out, replaced by vehicles equipped with bogies.

The advantage of train bogie

The advantage of the train bogie structure lies in its ability to rotate relative to the car body. At the same time, reducing the wheelbase (for the same bogie) makes it much easier to increase the number of axles. The most common type of bogie is the two-axle bogie, consisting of two wheelsets (two wheels per axle) and all devices related to the train's motion, which forms a two-axle truck that is then connected to the car body. 

Therefore, the train bogie is also called the running gear. Since the bogie itself is an independent component, it can be detached for maintenance, reducing the complexity of maintenance. To optimize the steering performance of the bogie, there is also a radial bogie, where the different wheelsets of the same bogie can continuously rotate towards the curve radius during steering, making the steering more flexible and allowing for easier passage through small radius curves.