Internal gears have a system whereby the gear shifting mechanism is built into the hub of the rear wheel. The most widely known form of internal gearing is the three or seven speed utility bicycle.
Internal gears are more reliable than derailleur gears, particularly for bicycles which are regularly exposed to wet weather or harsh elements. This is because the gear mechanism is cleverly contained and protected within the rear hub. Internal gears can also be shifted even when the bicycle is stationary (e.g. stopping at a traffic light), making them a perfect solution for urban city cycling.