A hub assembly for a wheelchair has a hub device and a switch device. The hub device has a hub shell, an axle, a ring and a ratchet. The ratchet has a cylinder section. The cylinder section has a recess formed in an outer surface of the cylinder section. The switch device has a pin and a wire. The pin is capable of being selectively inserted into the recess. The wire is securely connected with the pin. Because the pin is inserted into the recess and the ratchet engages the ring, the hub shell along with a wheel cannot be moved unintentionally backward on a ramp.一種輪椅上坡防倒退裝置,包括花鼓組件及限止組件,花鼓組件設有花鼓殼座及可單向轉動地位於花鼓殼座內的棘輪,於棘輪的外周面設有複數個凹槽;限止組件的插銷可選擇地插設於棘輪的凹槽內;在上坡時,因為棘輪已被插銷限止且棘爪部與棘齒部嚙合,所以花鼓殼座及輪子無法向後轉動;且由於花鼓殼座與棘輪的單向轉動機制,使得棘爪部與棘齒部在輪子前進時係呈空轉狀態,所以輪子仍可以向前轉動,十分方便實用,安全性極佳。12‧‧‧心軸132‧‧‧棘齒部142‧‧‧制動圓輪部1421‧‧‧凹槽22‧‧‧外殼231‧‧‧容置孔241‧‧‧限止部242‧‧‧抵部243‧‧‧穿孔244‧‧‧螺塊25‧‧‧支架251‧‧‧導孔26‧‧‧制動線271‧‧‧頭部272‧‧‧螺管部29‧‧‧彈簧
