Asmall-wheel bicycle, sometimes called amini velo ormini-velo,[1] is an adultbicycle with a reasonable sized frame and relatively smallwheels, usually ofETRTO 406 mm (20") or less nominal diameter, which is smaller than the common 622 mm (700c)road bicycle wheel size or 622 mm, 584 mm or 559 mm (29, 27.5 or 26")gravel andmountain bike wheel sizes common on most full-sized adult bikes.
They can be folding or non-folding. While manyfolding bicycles are small-wheel bicycles, not all small-wheel bicycles can fold. Some small-wheel bicycles neither fold nor separate, such as theMoulton, which comes in both fixed-frame and separable-frame versions.
WhileBMX bikes also have ETRTO 406 mm ("20 inch") wheels, they are not normally categorised as "small-wheel bikes".[2]
An early proponent of small-wheeled adult bicycles wasPaul de Vivie, better known by his pen name "Vélocio". His approach was to use a balloon-widthtire of about 57 mm (2.25″) on a 500 mm (20″) rim, giving a wheel of approximately 600 mm (24″) in diameter.[3]
The man credited with being the father of modern small-wheel bicycles isAlex Moulton who pioneered the field with his F-framedMoulton Bicycle in 1962. His original small-wheeled design notably featured full suspension. Raleigh introduced theRSW-16 as a direct competitor, but it lacked the suspension of the Moulton and compensated for this by using very wide 50 mm (2-inch) "balloon" tires. The RSW-16 "Compact" was a folding version. In 1968 Raleigh introduced theRaleigh Twenty, which later went on to become one of Raleigh's biggest sellers. A large number of European manufacturers made U-frame small-wheeled and folding bicycles in the 1970s.
Smaller wheels are more maneuverable.[4] For this reason, and in some cases for comic effect, they are used in someclown bicycles. Smaller wheels more faithfully follow the terrain, giving a harsher ride on bumpy roads that are effectively smoothed by larger ones.[4] It may be desirable for bicycles with smaller wheels to also be fitted with some form of suspension to improve riding characteristics. Bicycles with small wheels normally have theirgearing adjusted to provide the sameeffective wheel radius as large ones, sopedalling cadence is not different. Smaller wheels tend to weigh less than larger ones, thus bringing the performance benefits oflight wheels.
Small wheels, all else being equal, have slightly higherrolling resistance.[5] On the other hand, they have loweraerodynamic drag due to their smaller area, which is proportional to their radius.
The overall length reduction of a bicycle using smaller wheels depends on several factors, but mainly the wheel size and whether thewheelbase (distance between the front and rear axles) is reduced. For example, keeping the same axle distance, and going from a 40-622 wheel (approx. 702 mm diameter) to a 30-406 wheel (approx. 466 mm diameter) will result in an overall length reduction of 236 mm. Theoretically that reduction may be doubled if bringing the wheels closer together by shortening the axle distance.[citation needed] However, a shorter wheelbase may result in twitchiness or poor stability.[citation needed]
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