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A gravel bicycle is a type of bicycle intended for gravel cycling, including gravel racing. They are also sometimes known as "adventure bicycles", particularly ones intended for harsher off-road terrain.

While bicycles have been used for riding on such roads since bicycles were invented, the "modern" gravel bicycle, as a category, evolved in the 2000s, adopting technology from road bicycles, cyclocross bicycles and mountain bikes. They also share many characteristics of touring bicycles, such as relaxed geometry, wide tires and wide-range gearing.

A cyclo-cross bike or cyclo-cross bicycle (abbreviated CX Bike or CXB) is a bicycle specifically designed for the rigors of a cyclo-cross race. Cyclo-cross bicycles roughly resemble the racing bicycles used in road racing. The major differences between the two are the frame geometry, and the wider clearances that cyclo-cross bikes have for their larger tires and mud and other debris that they accumulate.

Cyclists have been competing in races on road-going bicycles since the 19th century. Cyclo-cross emerged as a sport in its own right in France in 1902. Cyclo-cross bicycles are similar to other bicycles, but the frame geometry is closer to a mountain bike than a road racing bicycle. The top tube is often longer and closer to horizontal, and the handlebars are higher, again akin to mountain bikes. The emphasis on bicycle handling skills differentiates cyclo-cross from road racing. Cyclo-cross courses are held on a variety of terrain, including grass, mud, sand and paved surfaces.