This frame (6) comprises a main tube (10), a head tube (22), a pedal assembly (32) forming a pedal circle (34), a seat tube (46) able to support a saddle (48). The saddle (48) is able to slide along the seat tube (46) in a plurality of intermediate positions between a fully retracted position and a fully extended position. The seat tube (46) is so arranged, with respect to the main tube (10), that, whatever the position of the saddle (48) is between the fully retracted position and the fully extended position, distances xa and xb satisfy a relationship: x a = A ∗ x b 0.9 A 0.95 wherein xa is the distance between an upper centre of gravity (52) of the saddle (48) and and the ground surface (4) and xb is the distance between the upper centre of gravity (52) a centre (36) of the pedal circle (34).