Ring and Pinion
The primary gear set in a differential that transfers rotational force from the driveshaft to the axles.
The ring and pinion is the primary gear set inside a vehicle's differential. The pinion gear is a small bevel gear connected to the end of the driveshaft. The ring gear is a large ring-shaped gear bolted to the differential carrier. Together, they convert the longitudinal rotation of the driveshaft into lateral rotation to turn the axles.
The ratio between the number of teeth on the ring gear and the pinion gear determines the vehicle's axle ratio (or gear ratio). For example, a 4.10 ratio means the driveshaft spins 4.10 times for every single rotation of the tires. This ratio multiplies the engine's torque and determines highway fuel economy and towing capacity.
Ring and pinion gears are machined to extremely tight tolerances and must be shimmed precisely during installation. If the gears are misaligned or if the differential runs low on gear oil, they will wear rapidly, creating a loud, high-pitched whining noise that increases with vehicle speed.