Bicycle frame structure having rear frame and front frame

A bicycle frame structure having a rear frame and a front frame, comprising:

• the rear frame of which a left stay and a right stay are bonded to each other, and an insert portion is formed at a bonded end portion;
• and
• the front frame where a head tube is formed at a front end portion thereof, an insertion hole into which the insert portion is inserted is formed at a rear end portion thereof, and the front frame is bonded to the rear frame along the circumference of the insertion hole,
• wherein the left stay comprises:
• a left stay outer panel disposed towards an outer direction, and
• a left stay inner panel disposed towards an inner direction and bonded to the left stay outer panel inwardly;
• wherein a right stay comprises:
• a right stay outer panel disposed towards the outer direction, and
• a right stay inner panel disposed towards the inner direction and bonded to the right stay outer panel inwardly;
• wherein the bicycle frame structure further comprises a first bonding portion where the left stay inner panel and the right stay inner panel are bonded to each other along a central axis between the left stay and the right stay,
• wherein end portions corresponding to the central axis are bent to have a first predetermined radius along the first bonding portion in the left stay inner panel and the right stay inner panel, respectively, and
• wherein the bent portions of the end portions having the first radius are line-contacted with each other to form a pivot point.