A tube connection assembly of a bicycle frame includes a bi-forked portion formed by a hollow rectangular tube; one end of the rectangular tube being bi-forked as two halves; each half having a positioning groove; and a combining portion formed by two plates which are connected as a shape corresponding to that of the positioning groove and the bi-forked portion so that in assembly the combining portion is assembled to the bi-forked portion; and connection area of the bi-forked portion and combining portion being welded.
A seat tube for a bicycle includes an upright tube, a head and an inner tube all of which are made of fiber reinforced material. The upright tube has an inserting portion at a top thereof. The head has an inside chamber and a sleeve portion at a bottom thereof. The sleeve portion of the head is sleeved onto the inserting portion of the upright tube such that the inside chamber of the head is communicated with an inside of the upright tube. An outer wall of the inserting portion of the upright tube is a taper face converging upward. The inner tube is disposed at a junction of the upright tube and the head and interconnected with the upright tube and the head. Thus, the seat tube has strong structure with light weight.
