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- reduce wind resistance, increasing aerodynamic efficiency;
- protect the skin against the repetitive friction of the legs against the bicycle seat or frame;
- provide support to the genitals, analogously to a jock strap;
- draw sweat away from the skin to prevent chafing and rashes, and to cool the rider down through the process of evaporation;
- compress the legs, which can help combat muscular fatigue;
- reduce the weight of a rider's clothing (compared to wearing denim, gym shorts or baggy shorts); and
- improve comfort during long rides with extra padding in the seat area called cycling pad.
Historically, cycling shorts were made of knit black wool, which hides oil and grease stains, with a chamois leather patch inside the shorts in the crotch area, which reduces chafing from the bicycle saddle. Modern cycling shorts are often made of spandex (Lycra) with a synthetic chamois which acts as an elastic interface between the cyclist's body and the saddle, and are produced in a variety of shapes and styles to suit the needs of different riders. For example, the patterns used for the chamois on women's cycling shorts tend to be quite different from those used for men's. The hem of each leg is usually lined with elastic and/or silicone that clings to the skin, keeping it in a fixed position. Shorts made from several panels (or cuts of fabric) fit better, but cost more.
Short-legged elastic tights commonly worn as street wear, under girls skirts and dresses, for gymnastics and ballet practice, or under athletic and running shorts are sometimes also referred to as bike shorts, but they are typically simpler and lighter garments than those worn by cyclists and generally lack the chamois or faux-chamois lining.
Bib shorts are cycling shorts that are held up by a bib (integral suspenders/braces) instead of an elastic waistband. Pro and serious riders tend to prefer bib shorts over non-bib shorts, due to the discomfort that often occurs with an elastic waistband, such as tightness (digging into skin) and chafing. The bib part of the short is often made of spandex and polyester with large sections of netting to help keep the rider cool.
The idea of modern bib shorts was a development from the braces (UK) or suspenders (US) that cyclists once used to hold up old-fashioned wool shorts, which had a tendency to become loose and heavy from riders' sweat (the use of braces/suspenders meant the shorts could be held up without an uncomfortably tight waistband). Bib shorts are well-suited to tall riders and riders with protruding stomachs because regular shorts can tend to fall down in the back while riding.
Baggy shorts (or shy shorts) are cycling shorts that look like regular shorts on the outside, but that are designed for cycling. Many have a chamois lining on the inside. This lining ranges from polyester fabric to full eight-panel, form-fitting cycling shorts beneath the baggier outside shorts. Others are designed to be worn with a separate liner short underneath. These shorts provide a more casual look when riding around town and off dedicated bike paths, and are also popular with many mountain bikers.