Sturmey-Archer

Sturmey-Archer is a manufacturing company originally from Nottingham, England. It primarily produces bicycle hub gears but has also produced motorcycle hubs.

The company was founded in 1902 by Henry Sturmey and James Archer under the guidance of Frank Bowden, the primary owner of the Raleigh Bicycle Company. In 2000, the assets and trademarks of Sturmey-Archer were sold to Sun Race of Taiwan which was renamed Sun Race Sturmey-Archer Inc and production moved to Taiwan.

All SA gear hubs use epicyclic (planetary) geartrains of varying complexity. The AW is the simplest, using one set of planetary gears with four planets. The AM uses three compound planets with differently sized cogs on a common shaft to engage the gear ring and sun gear separately, while the close-ratio three-speeds, and hubs with four or more speeds, use multiple planetary geartrains. Depending on the specific hub these may be in series with each other, or with one or the other set being selectable at any given time by locking a particular sun gear to the axle.

Sturmey-Archer's most widely known product is the AW three-speed hub gear, introduced in 1936 and still in production as of 2016. It is the survivor of a much larger range of "A" model three-speed hubs, including the AM (medium ratio for "club" riders), the AC and AR (very close ratio for time triallists) and the ASC (a unique three-speed fixed gear). In 1939 a four-speed model FW was released. This led to the development of a series of five-speed models, and by 1994, seven-speed hubs were introduced. Production was low, and in the mid-2000s these were discontinued.

The brief story of the Sturmey-Archer SW series medium-flange wide-ratio three-speed hub provides strong substantiation of the merits of the AW design.

Sturmey-Archer Gears Ltd. designed the type SW Mk. 1 medium-flange wide-ratio three-speed hub in 1954 and began production in 1956, intending it to replace the AW series of large-flange hubs.

Compared to the AW's 25% reduction in first gear, direct-drive second gear, and 33.33% overdrive 3rd gear, the SW offered slightly wider gearing, referred to by Brian Hayes as "super-wide" gearing, with 27.7% reduction for first gear, direct-drive second, and taller 38.4% overdrive third gear. Riders appreciate the nearly silent operation of its springless centrifugal pawls.

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Wikipedia