This article applies to Shimano 8-speed internal-gear hubs only. Another article on this site covers maintenance issues that apply generally to 4-, 7-, 8- and 11-speed Shimano internal-gear hubs:

• Anti-rotation Washers
• Brake Types
• Cable Adjustment
• Cable Installation
• General Advice
• Hubs Covered
• Links
• Lubrication
• Sprockets
• Upgrading Existing Bikes
• Vertical Dropouts

There are also articles on this site more generally about

• Internal-gear hubs
• Internal gear theory
• Shimano product lines and buzzwords

Read those articles along with this one. For more-detailed advice on installation of sprockets and setting the gear range, see the section on sprockets in the main article on internal-gear hubs.

The Nexus and Alfine 8-speed hubs have two stages of gearing. The first stage outputs either a reduction ratio or direct drive. The second stage offers direct drive and three higher ratios. The first stage is in its reduction ratio for first through 4th gear, while the second stage steps upward through its four ratios. Then the first stage switches to direct drive, and again, the second stage steps upward through its four ratios. The table below illustrates this. The bottom line of the table gives the ratio increment from the next lower gear.

For comparison, the Nexus 7-speed hub as a range of 244%, and the gear steps are more even:

Click here for an On-line Gear Calculator for Internally-Geared Hubs

The 8-speed hub is most efficient in 5th gear, with direct drive in both stages. 1st, 6th, 7th and 8th gear have direct drive in one of the two stages, while the power is transmitted through the gears for the others. In 2nd, 3rd and 4th gear, power is transmitted through the gears of both stages. Shimano has published a table illustrating the efficiency of power transmission, in this document, As the gear ratio increases away from direct drive, the efficiency decreases, as is to be expected, but the Shimano graph is a marketing tool, not a scientific report, and has no scale! The jump in efficiency between gears 4 and 5 is most noticeable. Jan Heine, publisher of Bicycle Quarterly magazine, finds it so annoying that he skips 4th gear entirely! Chester Kyle and Frank Berto have published an article in Human Power no. 52, (starting on page 3) with efficiency figures for the Nexus 4-speed hub, which is very similar to the second stage of the 8-speed, showing the expected drop in efficiency with higher gear ratios.

The hub's grease lubrication worsens its efficiency; Chester Kyle and Frank Berto identified this effect with other hubs. Relubricating with oil can reduce this problem. I have installed a Sturmey-Archer oil cap on my Nexus 8-speed hub -- more info.

A coaster brake or Rollerbrake further reduces efficiency, especially in cold weather.

Looking at the lowest row in the graph above, the ratio increments of the 8-speed are not very even. The relatively large jump between the bottom two gears is welcome, but then it appears again between gears 5 and 6. The small jump between the top two gears also is welcome, but it also appears between gears 3 and 4.

The Nexus and Alfine 8-speeds are more rugged than at least the older 7-speeds, but it have some well-known failure modes, and there are also well-known ways to prevent failure.

Aaron Goss, of Aaron's Bicycle Repair, reports:

Care should be taken to release force on the pedals when shifting. Applying power to a pawl which is partly engaged can damage the pawl. Shock loads have also broken other parts of the axle assembly. Aaron has photos of axles showing typical failures. He also recommends not standing to pedal on hills. Instead, shift down and spin. The Force limiter of the Alfine hub is probably intended to address this problem.

Hubs which shift by sliding a clutch along the axle do not have this problem, because the clutch will not release while the hub is under power.

Probably the most common failure, though, is due to insufficient lubrication, leading to contamination by water and dirt.

(Links to instructions may be found at the end of this section)

The Nexus 8-speed hubs have a overlocknut spacing ranging of 132 to 135 mm, as sold: see Shimano's overlocknut spacing chart. It is possible to reduce the spacing of the Nexus Rollerbrake/freewheeling models to as little as 126 mm by leaving off the Rollerbrake and using a narrower locknut. See our Rollerbrake page for instructions. This is not possible with the coaster-brake or disc-brake models Including the Alfine.

The internal mechanism of these hubs is complicated, and the usual repair is to replace the mechanism in its entirety. Shimano indicates little compatibility with hub shells of different models -- see the last two pages of this document -- but the internal mechanism can usually be replaced with a newer version as long as the hub is in the same series (with or without coaster brake; same number of roller clutches -- also be aware of other differences which may affect the design of the shell). See this Shimano document for description of some internal differences. You'll find details about interchangeability if you keep reading this page...

Shimano sells the axle assembly only as a unit and does not provide rebuilding instructions for it -- but you might disassemble it either by mistake or to cannibalize parts. Rebuilding instructions for the axle assembly are available on the Web site of Aaron's Bicycle Repair.

The right-hand hub bearing cup is vulnerable to damage from water contamination. Factory lubrication is inadequate, and better lubrication is advisable -- even with a new hub -- also, to make later cleaning and rebuilding easier.

The right-hand bearing cup is listed as a replaceable part in some parts lists. The old one would have to be extracted from the shell and a new one pressed in. If you succeed with this, please send advice, because that repair can save a wheel!

Do not lubricate the cassette joint (cable attachment parts): see advice in the Nexus technical article.

Basic models have a ratchet and pawls at the left side of the internal mechanism, and a roller clutch in the middle. Premium models have two or three roller clutches rather than only the one. These make only a very minor improvement in efficiency but are quieter than pawls and ratchets, and engage more quickly when resuming pedaling or changing gears. Coaster-brake models have at most one roller clutch.

A red band on the shell identifies a Nexus hub with needle-bearing pinions, for higher efficiency. The lower efficiency of 4th gear compared with the direct-drive 5th gear is noticeable on Nexus 8-speeds with plain-bearing pinions. Needle-bearing and plain-bearing pinions can be identified by their different appearance even in a fully-assembled gear-carrier unit. .

The SG-8R20, SG-8R22 and SG-8R31 have plain bearings; the SG-8R25, SG-8R27 and SG-8R45, needle bearings. Among models with a roller clutch at the left side, the SG-8R30, SG-8R31, SG-8R35 and SG-C6000 have plain bearings; the SG-8R36, SG-8R55, SG-8R56, SG-C6010 and SG-C6060, needle bearings. All Alfine hubs have roller-bearing pinions.

A drag spring raises additional issues, and is even used in some models without coaster brakes, to improve engagement of roller clutches. Reader Bruce Dance indicates:

While the axle assemblies are mostly identical, a section of the left end of the Alfine axle, as well as others, is fatter to withstand the bending moment from the optional disc brake, as shown in the image at the right (courtesy Aaron's Bike Repair). The Alfine left bearing cone threads onto the wider part of the axle. The Alfine requires a wider overlocknut distance than the Nexus without Rollerbrake. There are several different left-bearing-cone part numbers. Mix and match at your own risk.

The Rollerbrake and coaster brake are weatherproof, but drag slightly when not engaged, so if efficiency is a concern, avoid them. Smaller Rollerbrakes overheat when used on long downhill runs. We don't know for sure whether any coaster-brake model has needle-bearing pinions, but it appears not.

For all Nexus and Alfine 8-speed hubs except the S7000 series Alfine hubs, the cable is loosest in the lowest gear. The S7000 series is the opposite, and the cassette joint and axle assemblies are significantly different.

Bruce Dance sends the following warning:

Shimano has information on most but not all 8-speed models. These hubs have gone through several minor design changes, resulting in new model numbers and parts incompatibilities. Hubs parts numbers start with SG but there are also other parts listed, including brakes and shift levers. These pages are available in multiple languages, with a language list box at the upper right corner of the screen. All of the links below now go to the same page, and you ahve to drill down to get to the informaiton on specific models.

• Alfine cable-shifted models (click on buttons for different Alfine series)
• Alfine DI2 electrically-shifting hubs
• Inter-8 (Nexus)
• C6000 (a newer Nexus series)

Several Shimano dealer's manuals offer information on installation, adjustment and maintenance of newer hubs:

• For the SG-7051 series Alfine hubs
• For the SG-7000 series Alfine hubs
• For electrical-shifting SG-S505 Alfine and SG-8R60 and SG-C6060 series Nexus hubs
• Sprocket installation, wheel installation, cable shifting for the SG-8C31, SG-8R31, SG-8R36, and some SG-C60xx series Nexus hubs is covered in one manual.
• Dealer's manual for SG-C60xx 8-speed hubs, includes rebuilding information and dimensions.

Model numbers are of the form

• SG-S7xxx , for example, SG-S7000 for newer Alfine (disc brake) hubs.
• SG-S5xx for older Alfine hubs
• SG-C6xxx for newer Nexus hubs. These may have a Rollerbrake fitting, coaster brake or possibly threading for a band brake, depending on the individual model. A couple have both a coaster brake and disk brake fitting.
• SG-8Rxx for older Nexus freewheeling/Rollerbrake hubs. The first digit after the "R" represents the series, reflecting the number of roller clutches and whether the hub has cable shifting or electrical shifting. The greatest compatibility is within each series.
• SG-8Cxx for older Nexus coaster-brake models

Shimano made information sheets available individually for earlier hubs. The tables below list hubs in each series individually in order from newest to oldest, describing their differences, linking to information from various sources. The right-hand column holds links to available information. Shimano has provided rebuilding instructions for only one early model, though others are similar. There is information on rebuilding in the new dealer's manual for Nexus hubs.

To find which parts from newer models fit older ones, open the search function in your browser to look on this page for instances of an older hub's model number. Compatibility of the internal mechanism may cascade to yet another hub or hubs besides those indicated, as long as the shell is the same -- while brake fitting may differ. At the small-parts level, there is much more interchangeability than is shown. Parts for some older models may no longer be available.

There is some interchangeability between Alfine and Nexus models. When a model number in the interchangeability column is in italics, the entire internal assembly is compatible.

Ideally, the frame should have a dropout spacing of 127 to 135 mm to fit one of the Nexus hubs. Older bicycles are typically narrower than that. In the case of steel (Cromoly) frames, it is usually possible to spread the rear triangle to the needed width. Any good bicycle mechanic will be able to do this, or you can do it yourself. Alfine hubs require 135mm spacing.

If you leave off the Rollerbrake ®, you can get the spacing down to about 126 mm, as already mentioned. This is what I did on my Nexus bike. The Rollerbrake ® is a separate module, and when you buy the hub it is not even installed. (The brake unit would get in the way of fitting the spokes through the hub flange, so it has to be installed after the wheel has been built.)