Internally-Geared Hubs

A few years ago, during a dull stretch of bike touring, I tried to convince my riding partner of the merits of internally geared bicycles.

By Omar Bhimji

A few years ago, during a dull stretch of bike touring, I tried to convince my riding partner of the merits of internally geared bicycles. Obviously I did a poor job – she dismissed them as complicated and boring, and declared herself uninterested in the whole idea. If you’ll allow me, dear reader, I’d like to take another kick at the can.

Internally geared hubs date back to the late 19th century, and they duked it out with external gearing for a few decades before the derailleur (the little gadget that pushes your chain from one gear to the next) became the predominant bicycle shifting mechanism.

Externally, the set-up of an internally geared bicycle is quite simple – the bicycle’s chain wraps around the front chain ring and a single rear chain ring, like a single-speed drive train. Most internally geared hubs rely on internal planetary gearing to provide multiple gears from a single rear chain ring; instead of simply turning the hub of the bicycle’s rear wheel, the rear chain ring drives a mechanism inside the hub that delivers two or more gears.

The mechanism inside the hub is made up of one or more planetary gear sets, each of which is made up of a number of individual gears connected to one another – a central “sun” gear that is connected by several identical “planetary” gears to an “annulus,” an outer gear with inward-facing teeth. Each planetary gear set provides two gear ratios.

A basic Sturmey-Archer three-speed hub has a single planetary gear set, and delivers three different gears, like so:

Low gear – the rear chain ring drives the sun gear, which transfers this input through the planetary gears into the annulus, which directly drives the hub.

Middle gear/direct drive – the rear chain ring drives the annulus, which directly drives the hub. In this gear the sun and planetary gears are still spinning, they’re just not having any effect.

High gear – the rear chain ring drives the ring in which the planetary gears are held, with the planetary gears driving the annulus, which directly drives the hub. The sun gear in this configuration is stationary.

The more gears a hub has, the more planetary gear sets it will contain – each with a different ratio to produce different gears. Many companies make hubs with eight internal gears. Rohloff, a German company, manufactures a hub with 14 different gears, while Fallbrook Technologies, using spheres rather than gears and a design based on drawings by Leonardo da Vinci, has developed a hub called the NuVinci with infinitely variable gearing!

The advantages of internally geared hubs are numerous. Because all of the gears are internal, they are not exposed to dirt or the elements, and therefore require much less maintenance. They are also less susceptible to damage or wear and tear than derailleur-equipped bicycles. Shifting between internal gears can be accomplished even when the bike is stationary, eliminating the need to anticipate gear changes before stopping. Since the bicycle’s chain works in direct drive without having to move sideways, it can be easily covered or enclosed, protecting the rider’s clothing from damage and the chain from dirt and the elements. A direct drive set-up also means better chain line, and therefore better efficiency of power transfer between rider and wheel. Finally, because it has only one chain ring, an internal hub can be built into a wheel that is dishless – that is to say, a wheel that has spokes of equal length on both sides – and therefore stronger.

Internally geared hubs have their downsides as well. They’re often quite heavy, generally heavier than an equivalent externally-geared set-up. They can also be quite expensive, with eight-speed hubs costing between $200 and $300 and the 14-speed Rohloffs retailing for well over $1,000. Finally, with the exception of the Rohloff, they don’t offer the gear range of a modern front-and-rear derailleur-equipped set-up.

For serious utilitarian cyclists, internally geared hubs are worth considering. After nearly a century of existence, they’ve been developed to the point that they’re once again a worthy alternative to the derailleur.

1 Comment

  • Howard Abts

    Bhimji wrote: “Low gear – the rear chain ring drives the sun gear, which transfers this input through the planetary gears into the annulus, which directly drives the hub.” Of course not. The sun gear is of one piece with the axle, and does not turn.

    And again, “High gear – the rear chain ring drives the ring in which the planetary gears are held, with the planetary gears driving the annulus, which directly drives the hub. The sun gear in this configuration is stationary.” The sun gear in EVERY configuration is stationery.

    Seeing the date, April 1, makes me wonder whether this column was intended as a joke. If it was, not one reader in one hundred is going to recognize it as such. And what’s the funny part?

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