Fixed-gear bicycles are similar to single-speed bikes, with one glaring difference. Fixed gears do not allow the rider to coast with their feet on the pedals. The pedals continue to turn as long as the wheels are turning, similar to a child's tricycle. Typically, the term "fixed-gear wheels" refers to the single-speed workings that comprise the system.
Wheel Types
The type of wheels used with fixed-gear bicycles varies with the application of the bicycle. Spoke wheels are common on cruisers, road bikes and mountain bikes. Molded plastic wheels found on BMX and free-style bikes are often referred to as mag wheels, even though no magnesium is used in the fabrication. The particular wheels used with fixed-gear bicycles must accommodate the fixed-gear components in the rear wheel hub.
Hubs
Two types of rear hubs are used with fixed-gear bicycles: a fixed-gear hub and a flip-flop hub. Fixed-gear hubs have a single sprocket on the drive side of the rear wheel and a standard bearing cone on the opposite side of the hub. Flip-flop hubs have cogs for the sprocket on each side of the rear wheel hub. With flip-flops, fixed-gear or free-wheel is selected by removing the rear wheel and tuning it around in the rear wheel dropouts.
Gear Ratios and Sprockets
Bicycle wheels are not directly associated with gear ratios. The particular size of wheels is proportionate only to the number of rotations a wheel makes over a given distance. Gear ratio is the relative number of rotations of the front and rear sprockets. Fixed-gear bicycles have a single chainring at the pedal cranks and a single sprocket at the rear wheel hub. A typical fixed-gear ratio for road bikes would feature a 42-tooth chainring and a 26-tooth rear sprocket. Depending on the use of the bicycle, one or both sprockets can be changed to establish the preferred fixed-gear ratio.
Brakes
Many single-speed bikes have a coaster brake that works by reverse pedal pressure. However, since the fixed-gear system is constantly engaged, it is impossible to apply reverse pedal pressure. Side-pull caliper or disc brakes that operate with hand levers are used with fixed-gear bicycle wheels.
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