Underneath a train, each wheelset consists of two wheels—one on each side—firmly mounted on the same axle and generally used together with a bogie.

What is a Bogie?

A bogie is one of the most critical components in the structure of a rail vehicle. It plays a key role in ensuring the vehicle’s stability and passenger comfort. Each bogie typically comprises two wheelsets and is known as a two-axle bogie. A train car usually has two bogies located at the front and rear ends.

Why Do Trains Use Bogies?

Bogies serve two main functions: bearing loads and enabling turns. Bearing loads is straightforward—a fully loaded freight car might carry 60-70 tons of cargo, a weight far beyond what a standard vehicle axle with four wheels could bear.

Turning is essential because conventional trains use a locomotive to pull the cars, which do not have independent power, and the rails are fixed in position. This means the wheels on each car must be able to follow the rail and adjust direction accordingly. Notice that articulated buses typically have only a single axle on the trailer section to aid in turning. When multiple axles are needed to increase load-bearing capacity without impacting turning, bogies become essential.

High-Speed EMUs and Powered Bogies

The phrase “A train runs fast thanks to its locomotive” applies to conventional trains. However, high-speed EMUs are designed with distributed power and equipped with powered bogies. These advanced bogies include driving, transmission, buffering, damping, and braking mechanisms. When accelerating, each bogie on every car provides power to drive the entire train forward. When braking, all wheels engage to quickly bring the train to a stop.

The Importance of Bogies

Bogies integrate safety, stability, and comfort, supporting the entire train’s weight, adapting to curves, and ensuring a safe, smooth journey for passengers.

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