A sensor module for mounting on a rear fork of a bicycle includes a housing, a spool piece, a spool cap, and a sensing element. A switch member is arranged on one end of the housing, while a mounting seat is recessed on another end thereof. The spool piece is received by the mounting seat. The spool cap is arranged on the edge portion of the mounting seat. The sensing element is connected to the spool piece by a cable. The cable can be rewound into the spool piece. The distance between the sensing element and the housing is adjustable by extending or retracting the cable. The adjustability allows the sensor module to be adoptable by bicycles with different wheel sizes and rear fork structures. Accordingly, various cycling parameters can be measured.