Recumbent bicycle 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 rider's body presents a smaller frontal profile. A recumbent holds the world speed record for a bicycle, and they were banned from racing under the Union Cycliste Internationale (UCI) in 1934, and now race under the banner of the World Human Powered Vehicle Association (WHPVA) and International Human Powered Vehicle Association (IHPVA). 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. Description Recumbents can be categorized by their wheelbase, wheel sizes, steering system, faired or unfaired, and front-wheel or rear-wheel drive. Wheelbase 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. Wheel sizes The rear wheel of a recumbent is usually behind the rider and may be any size, from around 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. Given the higher rolling resistance of the smaller front wheel, loss of steering and control are somewhat more likely attempting sharp or quick changes of direction while crossing over patches of loose dirt, sand or pebbles. Larger diameter wheels generally have lower rolling resistance but a higher profile leading to higher air resistance. High-racer aficionados also claim that they are more stable, and although it is easier to balance a bicycle with a higher center of mass, 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. One common arrangement is 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 on a short wheelbase recumbent called "heel strike" (where the rider's heels catch the wheel in tight turns). A pivoting-boom front-wheel drive (PBFWD aka Moving Bottom Bracket recumbent) configuration also overcomes heel strike since the pedals and front wheel turn together. PBFWD bikes may have dual wheels or larger. Steering Steering for recumbent bikes can be generally categorized as over-seat (OSS) or above seat steering (ASS); under-seat (USS); or center steering or pivot steering. OSS/ASS is generally direct—the steerer acts on the front fork like a standard bicycle handlebar—but the bars themselves may extend well behind the front wheel (more like a tiller); alternatively the bars might have long rearward extensions (sometimes known as Superman