page_title: SCOA-P wheel
section_title: History
hierarchical_section_title: SCOA-P wheel / History
caption_attribution_description: English: Detail view of a 'SCOA P' driving wheel from a Victorian Railways J class 2-8-0. photo by zzrbiker
context_page_description: SCOA-P pattern wheels are a type of steam locomotive wheel. Rather than having traditional solid spokes, the SCOA-P spoke is hollow, with a 'U' shaped cross section. They are considerably lighter than a conventional spoked wheel or Boxpok wheel of the same size and strength.
context_section_description: SCOA-P wheels were developed in the late 1940s by the Steel Company of Australia Ltd (the P in the acronym standing for F. C. Paynter, who patented the design) in response to Victorian Railways experiencing fatigue problems with conventional spoked wheels. Stronger Boxpok type 'B' wheels had been installed on a number of VR locomotive classes in the late 1940s, but they had the disadvantage of being relatively heavy and also restricted maintenance access to axleboxes, underslung springs, and in some cases boiler washout plugs. Boxpok wheels were proposed for the forthcoming Victorian Railways R class 4-6-4, which had a relatively heavy 19.5-long-ton (19.8 t) axle load, but it had been discovered that the use of a Boxpok wheel would make coupling rod pin removal difficult. The SCOA-P wheel was developed to allow the strength of the Boxpok design but also provide the maintenance access of a conventional spoked wheel.
caption: SCOA-P wheel centre detail (tyre removed)
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