A bogie is a wheel or system of wheels and springs that is used to support a track or a belt. Found commonly in tracked vehicles such as crawler-type tractors and excavators as well as military tanks, the bogie wheels support the tracks by allowing the tracks to ride on them. Early snowmobile tracks depended on a system of bogie wheels to support the rubber track and give strength to the machine's suspension. When used in this application, the bogie wheels were spaced evenly on axles that run the length of the track between the drive axles. When used on a steel track such as a crawler tractor, the bogie wheels are typically arranged in a single line along the top and bottom of the track.
Unlike drive wheels or sprockets, the bogie wheel does not have a toothed or geared perimeter. The purpose of the bogie is not to power the track, but rather it is a support component with a smooth surface much like a tire. The track rides on the wheels and the wheels prevent the track from sagging and becoming bound up. On most steel tracks, the wheels are positioned between two rows of teeth protruding up from the track. These teeth create a roadway for the wheels to follow, preventing the track from sliding past the wheels as the vehicle makes sharp turns.
Most bogie wheels are constructed of solid steel with an axle, and maintaining the wheels requires little more than frequent greasing. Periodic inspection of the wheels is required to identify any damaged bearings or broken wheels. Often, the steel wheels will encounter a rock or other hazard that will cause the wheel to break. A broken wheel has the ability to damage a track and render the machinery useless until a costly and time-consuming repair has been completed. In most cases, changing a damaged wheel before it has affected other components is a relatively easy task.
Another frequently damaged bogie component is the spring. The spring is used to maintain pressure, which ensures the wheel remains in contact with the track as well as allows the system to flex as it encounters uneven terrain. When the spring breaks, the wheel may ride along off of the surface of the track. This creates an unsupported area that is prone to damage and breakage. Replacing broken springs is often a daily ritual with heavily used machinery.