A hub assembly includes a ratchet mechanism located between the hub and the tubular portion on one end of the hub, and including a driving member which is located in the tubular portion and is movable linearly. One side of the driving member has a cone-shaped first ratchet portion located axially and is composed of two triangular contact surfaces. A passive member is movable in the first slot and one side of the passive member has a cone-shaped second ratchet portion which is engaged with the first ratchet portion. A returning member unit is located between the hub and the passive member, and between the tubular portion and the driving member. By the triangular cone-shaped first and second ratchet portions, the contact area and the friction between the ratchet portions are reduced, and the engagement and disengagement is more quick and smooth.