One of 5 contact points on an upright bicycle
A bicycle saddle, often called a seat, is one of five contact points on an upright bicycle, the others being the two pedals and the two handles on the handlebars. (A bicycle seat in the specific sense also supports the back.) At any point in time there can be one, two, three, four or five contact points between rider and bike sharing support of rider body weight and applying rotation torque to the pedals.
The bicycle saddle has been known as such since the bicycle evolved from the draisine, a forerunner of the bicycle. It performs a similar role as a horse’s saddle, not bearing all the weight of the rider as the other contact points also take some of the load.
A bicycle saddle is commonly attached to the seatpost and