Shimano Nexus is a brand of bicycle components which includes products such as epicyclical gear hubs, cranksets, shifters, brake levers, hub brakes, hub dynamos, and a CPU for automatically changing gears. The series is primarily aimed at the "comfort" market such as urban commuters and tourers, and as such is not made to withstand the rigours of off-road or mountain biking. The free-wheeling Nexus internal gear hubs are compatible with Shimano's "roller brake", its version of a drum brake, but not with the Shimano disc brakes used with the higher-end Shimano Alfine internal gear hubs.
In 1995, Shimano rolled out its Nexus line of seven- and four-speed internal hubs. These had a new rotary actuator that did away with externally protruding gear shifting elements in the rear wheel. Also, the gear units were able to be shifted under moderate pedaling loads. Shimano had manufactured three speed hubs prior to that, and these hubs were at that point re-branded Nexus. In the early 2000s the 8-speed Nexus hub gear was introduced, having two stepped planetary series mounted downstream of each other. The hub was operated with a twist shifter. By November 2006, The Nexus range came in several ranges (Inter 3, Inter 7 and Inter 8) providing 3, 7 and 8 speed models respectively.
Internal gear hubs
Inter 3 - This hub has three speeds with 36% intervals and an overall gear range of 186%. It weighs 1220 grams stripped in its basic version (without built-in brake). Other versions include coaster, roller or disk brake. Starting from around 2011 Shimano offers a model with a rotary shifting mechanism similar to the one originally developed for the Inter 7 instead of the push rod/bell crank mechanism.
Auto 3 - The hub is fitted with a 3 speed automatic gear system, which utilizes a front hub dynamo to power a CPU that automatically changes the three speed internally geared hub. A similar system was built for the nexus 4.
Inter 4 - Nexus Inter 4 hubs had four speeds, but the same 186% range as the Inter 3. It only geared up, so a relatively large rear sprocket was necessary to give a reasonable development when combined with a normal front sprocket. It has been discontinued and spare parts have become hard to source.
Inter 5 - Apparently in 2012 Shimano has started making Nexus Inter 5 hubs. A forum discussion contains a link to one of two parts lists at Shimano. Range reportedly 0.75 to 1.545 for a total range of 206%. A glance on the Web confirms: Pricing seems to be near Inter 3, availability in the US seems limited. The Shimano 2013-2014 Products Line-Up Chart shows For Japanese market.
Inter 7 - The Inter 7 comes in two versions with either a steel or aluminium shell, weighing 1860 and 1460 grams respectively, the latter more expensive yet relatively reasonably priced. The gear mechanisms are operated with a Revo Twist Shifter or a simple non-ratcheting trigger shifter and are identical in the two versions, offering a range of 244% with non-even interval percentages of 17,14,17,16,17,16.
Inter 8 - The Inter 8 has interval percentages between the gears of 22,16,14,18,22,16,14, and a total range of 307%, comparable to a road bike derailleur gear systems, but as the other Nexus products, it is designed and intended for urban commuter use. The hub comes in a variety of versions, weighing between 1550 and 2040 grams stripped. The newest high end models are internally very similar to the Alfine model. The Inter 8 is more tolerant of shifting under load than the Inter 7.
The Shimano-invented "roller brake" works similarly to a drum brake, but is fitted to the side of the hub with a special adaptor ring. To provide better cooling the roller brake comes with an integrated cooling disc.
- Shimano tech doc for Nexus Inter 3 with "roller brake" installation instructions
- Shimano product spec page for Nexus Inter 7 indicating "roller brake" compatible
- Shimano product spec page for Nexus Inter 8 indicating "roller brake" compatible
- Shimano Assembly Manual for Nexus Auto-D 4
- Sheldon Brown about internal gear hubs
- mtbr forum thread - New Shimano 5-speed IGH
- NEXUS 5-Speed Internal Hub SG-5R35 parts list
- NEXUS 5-Speed Internal Hub SG-5R30 parts list
- Shimano 2013-2014 Products Line-Up Chart
- Sheldon Brown about the Inter 8