What Are Train “Trucks” Called?

They’re called bogies in most of the world and trucks in North America. In rail engineering, both terms describe the wheeled, pivoting assemblies beneath a locomotive or railcar that contain the axles, wheels, suspension, brakes, and sometimes traction motors; they support the vehicle body, help it steer through curves, and smooth the ride.

Names and Regions: Bogie vs. Truck

Railways use different words for the same component depending on geography and tradition. The distinctions matter for clarity in maintenance manuals, regulations, and engineering discussions.

• Bogie: Standard term in the UK, Europe, India, Australia, New Zealand, and much of the world.
• Truck: Standard term in the United States and Canada.
• Variant spellings: “Bogey” appears in some Commonwealth usage, but “bogie” is the dominant technical spelling.

Despite the varied terminology, industry professionals treat bogie and truck as equivalent: both refer to the multi-axle assembly under a rail vehicle.

What a Bogie/Truck Does

Beyond simply holding wheels, a bogie (truck) is a sophisticated system that manages load, stability, traction, braking, and guidance. Its design affects safety, speed, noise, and track wear.

Key Components You’ll Find

Modern bogies combine mechanical structure with suspension and, on powered units, electrical traction. The following items are common across passenger and freight designs.

• Wheelsets: Axles with wheels pressed on, including axle bearings.
• Side frames and transom/bogie frame: The structural skeleton that carries loads.
• Bogie bolster or center section: Transfers loads to the carbody via a center pivot/kingpin and side bearers.
• Primary suspension: Springs and dampers between axleboxes and frame to filter high-frequency track inputs.
• Secondary suspension: Air springs or coils between bogie and carbody for ride comfort and leveling.
• Braking equipment: Disc brakes or tread brakes, actuators, and rigging; on some systems, eddy-current or regenerative braking works alongside friction brakes.
• Traction components (on powered bogies): Traction motors, gearboxes, and couplings (e.g., nose-suspended or fully suspended motors).
• Steering and stability aids: Yaw dampers, anti-roll bars, radial steering linkages, and lateral stops.

Together, these parts let trains negotiate curves smoothly, stop reliably, and maintain comfort and stability at speed while minimizing wear on wheels and rails.

Common Types in Service

Manufacturers tailor bogies to service needs—from heavy-haul freight to high-speed passenger operations—balancing weight, speed, maintenance, and track friendliness.

• Two-axle bogie (most common): Fits many passenger coaches and freight cars.
• Three-axle bogie: Used for heavy loads or improved weight distribution (e.g., some locomotives).
• Jacobs bogie: Shared between two adjacent car bodies in articulated trains (e.g., some high-speed and light-rail sets) to save weight and improve stability.
• Powered vs. unpowered: Motor bogies provide traction; trailer bogies are unpowered and carry load.
• Radial/self-steering bogies: Allow axles to align more naturally with curves, reducing wear and noise.
• High-speed bogies: Optimized aerodynamics, stiffness, and damping for 200+ km/h service, often with advanced diagnostics.

The choice of bogie design directly influences performance metrics such as maximum speed, maintenance intervals, energy use, and passenger comfort.

When Trains Don’t Use Bogies

Not every rail vehicle rides on bogies. Some short, low-speed, or cost-sensitive designs use fixed axles without a separate bogie frame.

• Two-axle (rigid-frame) wagons: Each axle is mounted directly to the car frame; typical in light or short freight wagons and some heritage stock.
• Light trams and industrial vehicles: Occasionally use simplified running gear rather than full bogies.

These arrangements reduce complexity and weight but trade away the ride quality, curve negotiation, and speed potential of bogie-equipped vehicles.

Summary

The assemblies under railcars that carry wheels and suspension are called bogies globally and trucks in North America. They integrate wheelsets, suspension, braking, and sometimes traction to guide, support, and stabilize trains. While some simple vehicles use fixed axles, most modern passenger and freight equipment relies on bogies/trucks tailored to their service demands.

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