[me and my metro]

The tone ring is mounted to the carrier inside the differential. The speedometer is calibrated by rotations per mile based on tire size. Changing the gear ratio in the differential does not change number of times the carrier turns per mile. If you change tire sizes you need to recalibrate your speedometer with this type of setup. The sensor and the tune ring generates a low voltage AC signal based on speed that is interpreted by the pcm and converted to the speedo signal.