THESE ARE "Wired" speedometers. "Wireless" get disrupted by the magnetic field generated by a motorized bike - so I only recommend "Wired" bicycle computers/speedometers.
GREAT VALUE! I have had good success with this model [wired] speedometer with my motored bicycle builds. I have had no success with wireless.
I think it has something to do with vibration from engine or electro-magnetic field from generator.