Editing Bogie (section)

===Purpose===
[[File:Bogie Vehicle Schematic-en.svg|thumb|Bogies allow the [[Wheelset (rail transport)|wheelsets]] to more closely follow the direction of the rails when travelling around a curve in the railroad.]]
[[File:Indirect truck.gif|thumb|200px|Displacements of a bogie]]
Bogies serve a number of purposes:<ref name="how">{{cite journal | author = Isao Okamoto | date = December 1998 | title = How Bogies Work | journal = Japan Railway & Transport Review | issue = 18 | pages = 52–61 | url = http://www.jrtr.net/jrtr18/pdf/f52_technology.pdf | url-status = dead | archive-url = https://web.archive.org/web/20070927202523/http://www.jrtr.net/jrtr18/pdf/f52_technology.pdf | archive-date = 2007-09-27 | access-date = 2018-11-30 }}</ref>
* supporting the body of the rail vehicle
* running in a stable manner on both straight and curved track
* improving [[ride quality]] by absorbing vibration and minimizing the impact of centrifugal forces when the train runs on curves at high speed
* minimizing generation of track irregularities and rail abrasion.

Instability can occur when a combination of bogie design, springing, vehicle and bogie wheelbase, and track dynamics, cause the bogie to oscillate at high speed – a phenomenon known as "hunting". If unchecked, derailment can occur. Cars experiencing hunting are removed immediately once the defect is discovered. A tendency for more than one vehicle to hunt will result in investigations with a view to re-designing.<ref>{{cite book |title= South Australian Railways annual report 1946-47 |date= 1947 |location= Adelaide |publisher= [[South Australian Railways]] |page=17 }}</ref>

Usually, two bogies are fitted to each [[Railroad car|carriage]], wagon or [[locomotive]], one at each end. Another configuration is often used in [[articulated vehicle]]s, which places the bogies (often [[Jacobs bogie]]s) under the connection between the carriages or wagons.

Most bogies have two axles,<ref name="how" /> but some cars designed for superior riding qualities or heavy loads have more axles per bogie. Heavy-duty cars may have more than two bogies using [[span bolster]]s to equalize the load and connect the bogies to the cars.

Usually, the train floor is at a level above the bogies, but the floor of the area between the bogies may be lowered to increase interior space while staying within [[Loading gauge|height restrictions]]. Examples are [[Well car|container well cars]], [[bilevel rail car|bi-level passenger cars]] or stepless-entry, low-floor cars on railways with near-ground-level platforms.