Hub Gear - Hybrid Gearing With Derailleurs

Hybrid Gearing With Derailleurs

Some systems combine internally geared hubs with external derailleurs. A freewheeling hub with a sprocket suitable for narrow chain can be combined with a double or triple crankset and front derailleur, in order to provide a wider range and closer gear ratio spacing. A chain tensioner or a rear derailleur is needed to take up chain slack, and care is needed not to over-torque the hub by using too small a chainring/sprocket ratio.

Alternatively, some hubs can accept two dished drive sprockets, between which the rider can switch with a rear derailleur. Careful sprocket selection can allow the available gear ratios when using one sprocket to fall half-way between those available when using the second sprocket, providing half-step gearing, as on the Brompton 6-speed folding bicycle. This concept is used and extended in the SRAM Dual Drive system, where a conventional multi-speed cassette is mounted to a 3-speed hub. A similar version of the ever-popular AW hub is manufactured by Sturmey Archer. This system may be useful on bicycles which cannot accept a front derailleur. The German company Canyon introduced the 1442 in 2010, a hybrid hub which uses a similar epicyclical/derailleur combination.

When both front and rear derailleurs are used with a geared hub, the result is a very wide-ranging drivetrain, at the expense of increased weight and complexity.

A particular use of the dualdrive systems is on recumbent bicycles where starting off from a standstill, or after braking hard, is very difficult if a high gear is engaged. On an upright bicycle, if a high gear is engaged, the rider may use one leg to gain minimal momentum and stand on the pedals and use his upper body to balance the bike; this is not possible on a 2-wheeled recumbent bicycle. Here the dualdrive setup allows shifting at a standstill or at low speeds, which is not possible with derailleur gears alone.