Another article on this site covers topics common to many Sturmey-Archer hubs. Please read that article to learn about

• Date and model identification
• Cable replacement
• Cable adjustment
• Cone Adjustment
• Anti-rotation washers
• Axle length
• Lubrication

There are also articles on this site more generally about

• Internal-gear hubs
• Disassembly of Sturmey-Archer hubs
• Special alignment and adjustment (Dynohubs, hub brakes, shifter parts)
• Use and maintenance of Sturmey-Archer hubs
• Parts and names (older Sturmey-Archer hubs)
• Sturmey-Archer corporate history and hub models

he 8-speed Sturmey-Archer hubs have an innovative, modular design with 3 planetary systems one after the other. If a module's sun gear is locked to the axle, it gears up, and if not, the module operates at unity ratio. Each of the three modules has a different ratio. The eight combinations offer eight different speeds.

Because these hubs only gear up, they require a much smaller chainwheel than other hubs and are especially well-suited to a small-wheel bicycle. These hubs are most efficient in the lowest gear, which passes power directly from the driver to the hub shell, and least efficient in the highest gear, which uses all three modules.

The ratios for the wider-ratio series introduced in 2009 -- X-RF8(W) etc. -- are:

Those numbers are to only two decimal places, as no detailed technical information is available as of June, 2010.

The ratios for the first series of 8-speed hubs -- X-RF8 etc. -- are:

These numbers are based on gear-tooth counts.

Also see Sheldon's Internal Gear Calculator.

It is difficult for a simple planetary system to achieve a ratio near unity, and so the bottom step is large with these hubs. To avoid a large jump in the middle of the range, the large jump is used again at the top of the range. For this reason, it is best to set the second-highest gear as the level-ground cruising gear, around 75 gear inches (6.0 meters development, 5.5 gain ratio). Setting any lower gear as the level-ground cruising gear would make the top gear too high to be useful. On the other hand, if you ride in flatlands so you don't need any very low gears, your might ignore this advice in order to get more gears in the level-ground gear range.

There is more detailed information on sprockets and on setting the gear range on another page. Also see Sheldon's take on setting the gear range for this hub, on his 8-speed Raleigh Twenty page. Different (pedal) strokes for different folks...

A few technical issues are important when specifying, installing or rebuilding these hubs:

• These hubs are available with no brake, or with a drum brake or a disk brake fitting. The discontinued X-RR8 was available with a roller brake.
• The sprocket is unlike the one used on most other internal-gear hubs. The center hole is much larger, and the sprocket is available only with 19, 23 or 25 teeth. The sprocket has three lugs and is held in place by a circlip (snap ring).
• This hub is especially well-suited to older bicycles with narrow rear dropout spacing. By the choice of locknuts and by using the brakeless version of the hub, the overlocknut distance can be smaller than for any other internal-gear hub with 7 or more speeds -- as little as 115 mm. The overlocknut distance also can be as great as 135 mm.
• Sturmey-Archer sells cranksets adapted to this hub, with tooth counts in the 30s, and designed to work with a full chain case.
• These hubs have rotary shifting and use different shifters from other Sturmey-Archer hubs.

The new wide-ratio models are very similar to discontinued models, but a different tool is required to remove the screw-in right ball cup, and obviously, many of the internal parts are different. No technical information on the new models is available online as of yet (June, 2010).

Technical documentation is available for these models.