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The Internals of Internal Gears

By Brad Quartuccio

Internally geared hubs are popular amongst city cyclists for a number of reasons, not the least of which is that they are pretty well maintenance free. Things can and do go wrong with internally geared hubs, but the majority of people aren’t going to want to open them up and find a fix, the guts can be dauntingly complex. The pictured Shimano Nexus three-speed hub and coaster brake is fairly simple as far as these hubs go, yet as one can see there is a lot going on to fit both a shifting and braking system inside the hub body. A series of planetary gears translate the rotation of the cog to the rotation of the hub body and wheel, making the hub spin faster or slower than the cog depending on gear choice, with a freewheel mechanism for coasting and a braking system for stopping. Remarkably reliable for as many parts are jammed inside, from a performance standpoint the main drawback to an internal hub is the added efficiency losses inherent in their design. That, and of course the fact that if anything does go wrong you’re likely out of luck until you can make it to your local shop with a mechanic well versed in hub rebuilds and the small touches separating one model from another. You won’t be fixing one of these by the side of the road.

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