The spider gear lies at the centre of a differential case and is free to rotate in two ways. It can rotate along the ring gear and can also spin on its own axis. The manner in which the spider gear moves controls the direction in which the car moves.
The power from the engine passes to the ring gear through the pinion gear. There is a connection between the ring gear and the spider gear. Firstly, the power flows from the drive shaft to the pinion gear. As the pinion gear connects to the ring gear, the power then flows through the ring gear. Since the spider gear connects to the ring gear, the power further flows into the spider gear.
The spider gear meshes with the side gears. Hence, the power flows to both the side gears. When the spider gear rotates along the ring gear but does not rotate around its axis, the vehicle is moving straight. In this case, the spider gear makes the side gears turn and both rotate at the same speed.
When the car takes a right turn, the spider gear turns along with the ring gear and also rotates around its axis, the left side gear has a greater speed in comparison to the right side gear. When the car takes a left turn, the spider gear spins in the opposite manner and the right side gear has a greater speed.