Generally, bicycles are vehicles that are moved by pushing pedals with two feet. In a broad sense, bicycles include vehicles having three or four wheels and vehicles moving in places other than the ground, for example, a water bicycle or an ice bicycle. Bicycles are widely used as representative transportation means using human power. Recently, bicycles have been used as sports equipment for the promotion of health, and in addition, have been widely applied as recreation means. Further, due to the environment-friendly characteristics of bicycles, the demand for bicycle has steadily increased.
A conventional bicycle includes wheels, a frame, pedals, a chain, a saddle, handlebars, and other parts. Generally, the bicycle is provided with a height adjustment unit for adjusting the height of the saddle at the junction between the saddle and the frame. Thus, even if users of various heights ride the bicycle, the height of the saddle can be adjusted to be appropriate for the height of the user so that his or her feet comfortably reach the pedals. As a result, the user can ride the bicycle stably.
As such, in the conventional bicycle, the height of the saddle may be adjusted in a vertical direction so that the interval between the user's feet and the pedals can be adjusted. However, even if people are the same height or their legs are the same length, the lengths of their upper bodies or arms may be different from each other. Thus, when the length of one's legs is much greater than the average length, and the height of the saddle is adjusted according to the length of the legs, it will be difficult to grip the handlebars with the hands. Conversely, when the legs are short, the arms must be bent when gripping the handlebars. In these cases, it is inconvenient to ride the bicycle for a lengthy period of time.
Further, when a user goes up or down a steep hill while riding the bicycle, his or her body leans toward the front or rear portion of the bicycle. At this time, because the angle of the saddle is fixed, the user is uncomfortable, so he or she frequently stands up rather than remaining on the saddle. However, when the user stands up and puts his or her weight only on the pedals, stability is low and the possibility of accidents is thus increased. Further, while the user goes up and down a hill for a lengthy period of time, he or she must continue standing up, which is fatiguing.