A ratchet mechanism of a hub assembly is located between the hub and the tubular portion, and includes a driving member which is movable linearly in the tubular portion. 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 fixed in the hub and has a cone-shaped second ratchet portion which is engaged with the first ratchet portion. A returning member is located between the hub and the driving member. The passive member is fixed to the hub easily. By the triangular cone-shaped first and second ratchet portions, the contact are and the friction between the ratchet portions are reduced, and the engagement and disengagement is more quick and smooth.