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Also called "hub gearing" or "hub gears," these rear hubs (the centermost part of the wheel) have the gearing system inside. Small "planetary gears" hidden inside the hub change position as you operate the control lever to shift and this makes it easier or harder to pedal. Hub gears are heavier than derailleur shifting systems but are less affected by weather and wear and tear. They are commonly used on commuting and city bicycles.