A recumbent bicycle is a bicycle that places the rider in a laid-back reclining position. Most recumbent riders choose this type of design for ergonomic reasons; the rider's weight is distributed comfortably over a larger area, supported by back and buttocks. On a traditional upright bicycle, the body weight rests entirely on a small portion of the sitting bones, the feet, and the hands. Most recumbent models also have an aerodynamic advantage; the reclined, legs-forward position of the riderís body presents a smaller frontal profile. A recumbent holds the world speed record for a bicycle, and they were banned from racing under the UCI in 1934,[1] and now race under the banner of the Human Powered Vehicle Association (HPVA). Recumbents are available in a wide range of configurations, including: long to short wheelbase; large, small, or a mix of wheel sizes; overseat, underseat, or no-hands steering; and rear wheel or front wheel drive. A variant with three wheels is a recumbent tricycle. Wheelbase Bacchetta Corsa, a short-wheelbase high racer Long-wheel-base low-rider recumbent with steering u-joint (UA) Long-wheelbase (LWB) models have the pedals located between the front and rear wheels; short-wheelbase (SWB) models have the pedals in front of the front wheel; compact long-wheelbase (CLWB) models have the pedals either very close to the front wheel or above it. Within these categories are variations, intermediate types, and even convertible designs (LWB to CLWB) - there is no "standard" recumbent. [edit]Wheel sizes The r

ar wheel of a recumbent is usually behind the rider and may be any size, from around 16 inches (410 mm) to the 700c (or 27" on some older models, as on upright road bikes of that time) of an upright racing cycle. The front wheel is commonly smaller than the rear, although a number of recumbents feature dual 26-inch (ISO 559), ISO 571 (650c), ISO 622 (700c), or even 29 x 4" oversize all-terrain tires. Larger diameter wheels generally have lower rolling resistance but a higher profile leading to higher air resistance. Highracer aficionados also claim that they are more stable, and although it is easier to balance a bicycle with a higher center of mass,[2] the wide variety of recumbent designs makes such generalizations unreliable. Another advantage of both wheels being the same size is that the bike requires only one size of inner tube. The pivoting-boom front-wheel drive Flevobike racer with 700c wheels (NL) Cruzbike Silvio (2009) A moving bottom bracket, front wheel-drive, 700C road bike (with rear rack). The most common arrangement is probably an ISO 559 (26-inch) rear wheel and an ISO 406 or ISO 451 (20-inch) front wheel. The small front wheel and large rear wheel combination is used to keep the pedals and front wheel clear of each other, avoiding the problem called "heel strike" (where the rider's heels catch the wheel in tight turns). A pivoting-boom front-wheel drive (PBFWD) configuration also overcomes heel strike since the pedals and front wheel turn together. PBFWD bikes may have dual 26-inch (660 mm) wheels or larger.