Measuring instruments are frquently provided on the handlebar of a bicycle for indicating to the cyclist relevant operational data like the actual speed or the covered distance. These instruments are detachably mounted on the handlebar so that they can be removed particularly in view of the danger of theft when the bicycle is parked in a place accessible to the public. The electronic instrument is supplied with signals from a signal receiver which is mounted on a fork leg of a bicycle fork unit carrying a bicycle wheel. The signals are generated in the signal receiver by a signal inducer fastened to a spoke of the respective wheel. In order to permit easy detachment of the instrument from the instrument carrier fixed to the handlebar the cable is connected to the instrument carrier and is in electrical connection with electrical contacts provided on the instrument carrier. Counter-contacts are provided on the instrument. The counter-contacts are electrically connected to the contacts when the instrument is engaged with the instrument carrier.