Sturmey-Archer

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A Sturmey Archer three speed AW gear, the most common kind of Sturmey Archer gear

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 (1857–1930) and James Archer under the guidance of Frank Bowden, the primary owner of the Raleigh Bicycle Company.[1] 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.[2]

Products

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.

AW hub gears

An exploded Sturmey Archer AW

Sturmey-Archer's most widely known product is the AW three-speed hub gear, introduced in 1936 and still in production as of 2015. 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.

SW hub gears

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.[3]

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,[3] 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.

Exploded View & Parts List of Type SW three-speed Mk. 1. Sturmey-Archer Gears Ltd., 1954.

Smaller and lighter than an AW hub, the SW has fewer parts and was thought to be less costly to manufacture than the AW series that had been in continuous production since 1936.

The new hub turned out to be slow to shift and can't be 'pre-shifted' like an AW. More troubling, the unique crescent-shaped pawls can have slippage issues even when a gear is fully engaged, especially if the hub had not been continually supplied with fresh 10W oil.[4] Production of the SW series ceased after two years, 1956-57.

Sturmey-Archer had maintained reduced AW series production during these years to aid cycle makers in the transition to the new hub. On terminating SW production in 1958, the company resumed previous levels of AW production.

After the failure of the SW in the market and the re-commitment to the AW, Sturmey-Archer began to widely license the design, with fully interchangeable clones of the AW eventually being made under labels including J.C. Higgins, Sears, Austro-Daimler, Brampton, SunTour, and others.

Dynohub

The Dynohub was Sturmey-Archer's hub dynamo for bicycles. The Dynohub was designed to generate electrical lighting power for bicycles during the Second World War. The initial GH12 12-volt model was introduced in 1936 followed several years later by the GH8. This 8-volt unit was in turn supplanted in the 1950s by the lighter-weight GH6 6-volt version, which remained in production through the early 1980s. The term "dynohub" is sometimes applied generically to bicycle hub dynamos, but it originates as a trademark.

The GH6 version produced a rated output of 6 V, 0.33 A (2 W) from a 20-pole ring magnet with a stator having a continuous winding. Original headlamp bulbs are 6 V, 0.25 A (1.5 W) (e.g., CRY5) and a rear bulb of 6 V 0.04A (0.24W) (e.g., CRY8). This is different from a modern standard bicycle dynamo, though replacements can still be had.[5] Common substitutions are the modern standard 2.4 W headlamp bulb and a tail lamp bulb of 0.6 W. One rider reports much more light with a 6.3 V, 0.25 A (1.6 W) type 40 bulb.[6]

Rated output was reached at around 20 km/h (12 mph), a rotational speed of approximately 60 rpm. The name dynamo implies DC output, but as usual with bicycle dynamos (known as generators in North America), output was in fact alternating current.

Dynohubs were offered as front hubs and as rear geared hubs. The AG was an AW three-speed rear hub with inbuilt dynamo, while the FG was a dynamo similarly combined with an FW four-speed.

Hub generators were absent from Sturmey-Archer's product range from the 1980s until the 2006 introduction of the X-FDD front hub, which combines a 6v, 0.4 A (2.4 W) or 0.5 A (3 W) dynamo with a 70 mm drum brake.[7]

Modern gear hubs (Sunrace Sturmey Archer)

The XRF8, XRD8, XRR8, and XRK8 8-speed hubs entered series production in 2007.[8]

SunRace Sturmey Archer have modified the design and manufacture in many respects; compared to the old AW hub, the current three-speed equivalent (SRF3) now has an aluminium alloy shell for lighter weight. According to Schraner and Brandt, an aluminium alloy shell reduced spoke breakage due to aluminium being softer allowing the spoke to seat into the flange and disperse the stress at the bend in the spoke over a wider area.[9][10]

Three-speed fixed gear hub

In 2009 Sunrace Sturmey-Archer re-introduced a three-speed fixed gear hub, the S3X.[11] This gives ratios of 100/75/62.5 (i.e. the top gear is direct drive and the others are geared down from it) and the internals are based on the newest five-speed freewheel hub (in the same way as the original fixed ASC was based on the contemporary FC four-speed hub).

Other

The Sturmey-Archer name was also credited with the 49 cc two-stroke engine fitted to early Raleigh mopeds, although this was actually a reworking of Vincenti Piatti's "Trojan Mini-Motor" and built by BSA's motorcycle operation.[12]

References

  1. ↑ Sturmey Archer Heritage website
  2. ↑ The Sturmey-Archer Story supplement
  3. ↑ 3.0 3.1 Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ Commercial cycle bulb supplier
  6. ↑ GH6 Dynohub Head Lamp and Tail Lamp Bulbs
  7. ↑ Sturmey-Archer Historical Hub Archive. Retrieved on 2007-10-24.
  8. ↑ Sturmey-Archer gear hubs
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Raleigh Moped history

External links

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