Hub

A hub comprising:

• a hub body;
• a ratchet wheel assembly disposed in the hub body and comprising:
• an outer ratchet wheel including an annular tooth surface positioned on an end face of the outer ratchet wheel and multiple ring teeth positioned on a peripheral face of the outer ratchet wheel,
• an inner ratchet wheel including an annular tooth recess located on an end face of the inner ratchet wheel and multiple inner ratchet teeth positioned on a peripheral face of the inner ratchet wheel;
• and
• a ratchet seat engaged with the ratchet wheel assembly and comprising:
• multiple inner ring teeth engaged with the outer ring teeth and dispositioned on an inside face of the ratchet seat and corresponding to the outer ring teeth;
• wherein, a tooth-face length of the inner ring teeth is shorter than a tooth-face length of the outer ring teeth;
• and,
• wherein, the ratchet wheel assembly is coaxially and movably disposed in the hub body, the annular tooth surface of the outer ratchet wheel and the annular tooth recess of the inner ratchet wheel are engaged with each other to allow the hub body and the ratchet seat to achieve a synchronous rotation state or an asynchronous rotation state;
• when the hub body and the ratchet seat are in the asynchronous rotation state, the outer ratchet wheel is axially moved relative to the ratchet seat.