# Span bolster

> Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Span_bolster
> Markdown URL: https://mediated.wiki/source/Span_bolster.md
> Source: https://en.wikipedia.org/wiki/Span_bolster
> Source revision: 1331243626
> License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/)

Tool used in railway engineering

This article needs more citations. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Span bolster" – news · newspapers · books · scholar · JSTOR (December 2009) (Learn how and when to remove this message)

Span bolsters can be seen at both ends of this diagram of the [14"/50 caliber railway gun](/source/14%22%2F50_caliber_railway_gun).

Span bolsters (white/orange) in a [Schnabel car](/source/Schnabel_car)

A **span bolster**, in [rail terminology](/source/Rail_terminology), is a beam or frame used to link two trucks ([US](/source/US_English)), or [bogies](/source/Bogie) ([UK](/source/British_English)), so that they can be articulated together and be joined to the [locomotive](/source/Locomotive) or [railroad car](/source/Railroad_car) at one rotating mounting point. In effect, they make one "super-truck" out of the two, while permitting each truck to move relative to the other.[1]

## Use

### Locomotives

The most common use on [locomotives](/source/Locomotive) is to give a more flexible alternative to a four-axle truck; two two-axle trucks linked by a span bolster allows the wheels to follow a curve better, without excessive side forces or the need for [lateral motion](/source/Lateral_motion_device) of the axles in the truck. The use of a span bolster is normally signified in the [AAR wheel arrangement](/source/AAR_wheel_arrangement) notation by a + sign; thus a locomotive with two span bolsters, each with two two-axle trucks (the most common arrangement) is a [B+B-B+B](/source/AAR_wheel_arrangement#B.2BB-B.2BB).

### Freight cars

Span bolsters have been used for some high-capacity [freight cars](/source/Freight_car). The most common use is for large [flatcars](/source/Flatcar) to haul very heavy loads. These cars need many axles to distribute the weight. Specialized [Schnabel cars](/source/Schnabel_car) with up to 72 wheels have been built for carrying heavy items. Often the span bolsters connecting the trucks are connected by additional span bolsters to the car. The use of span-bolster-connected trucks is essential to allow the load to be transported through curves.

## See also

- [Whippletree (mechanism)](/source/Whippletree_(mechanism))

## References

1. **[^](#cite_ref-vd_1-0)** Dukkipati, Rao (2000). *Vehicle dynamics*. Boca Raton, Fla. New Delhi: CRC Press Narosa Pub. House. p. 317. [ISBN](/source/ISBN_(identifier)) [084930976X](https://en.wikipedia.org/wiki/Special:BookSources/084930976X).

---
Adapted from the Wikipedia article [Span bolster](https://en.wikipedia.org/wiki/Span_bolster) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Span_bolster?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.