Here, see for yourself.
"Mazda speed sensors are one of the four major components in our Mazda vehicle’s anti-lock braking system, and are found along with the pump, valves, and controllers. The speed sensor’s job is to initiate the process so as to the other three parts can do their functions well. It is also the speed sensor’s job to know just how fast your car is moving. It is also the speed sensor that provides information that is needed by the system to know when a wheel is just about to lock up. To be able to provide the much needed information, the speed sensors are actually located at each wheel and also in the differentials in some cases.
Your car’s speed sensor is artfully designed to be able for it to record the rate at which your car’s crankshaft is spinning. The Mazda speed sensor is actually a wireless sensor that measures speed and distance. It converts these parameters electronically. It measures these parameters thru a magnet rotating. Once these physical parameters have been converted to an electrical equivalent, it is then easily input for manipulating, analyzing, or displaying. "
Spinning your wheels will not produce a faulty speed/time/distance calculation. If your speedometer changes when you spin your wheels than there is something wrong with your vehicle.It was my understanding that the sensors were at your back wheels only, but it appears they are on all four wheels as they have multiple functions.
