The interest towards piezoelectric energy harvesters has been fostered in recent years by the development of ultra-low power electronics. An experimental analysis approach based on modal testing is here proposed in order to detect the best position on a bicycle of a piezo-harvester. Road tests show that vibrations are in the low frequency range so that the energy harvester has to be properly tuned to get its largest electrical response. Different tuning strategies of the same piezo-harvester, mounted in the best location, are tested and compared. The best setup is selected by considering as figures of merit the average stress inside the piezo-layer of the harvester (which affects its lifespan) and the maximum electric power which can be harvested. These figures are both analytically estimated from the measured power spectral density of the output open circuit voltage, which is experimentally determined. It is shown that the configuration with the largest tip mass provides the largest delivered power. Nevertheless, in order to preserve the device lifespan, harvesters with oscillator and liquid tip mass may represent a good tradeoff between the amount of generated stress and delivered power. The methods presented in this paper can be also adopted for predicting the behavior of harvesters mounted on other light vehicles.