A magnetic device mounts on a flat spoke of a wheel. This magnetic device can comprise a magnet and a housing. The housing is coupled to the magnet, and has a spoke-receiving recess with a non-circular cross section, and at least one detent. The detent extends from the housing into the spoke-receiving recess to secure a flat spoke within the spoke-receiving recess via a snap-fit. The magnetic device communicates with a sensing device, which is adapted to be coupled to a portion of the bicycle that is adjacent to a wheel of the bicycle. A display unit, adapted to be mounted on handlebars of the bicycle, displays the speed information obtained from the sensing device. In a second embodiment, the housing is made of a more elastic material, and the detents become optional. In a third embodiment, the spoke-receiving recess of the housing has a projection that engages a concavity form in the connecting portion of the spoke. In a fourth embodiment, the spoke-receiving recess of the housing has a concavity that engages a projection form on the connecting portion of the spoke.