PAS for 50 Rebels e-bikes. Speed sensor. PAS is an abbreviation for Pedal Assist System, and it's a general term for devices that power the motor automatically when you pedal without the need to press a throttle on the handlebars. They can do this in response to the speed that you are spinning the cranks, the torque that you are applying to the pedals, or some combination of those. Ebikes with this behaviour are often called pedalecs.