What is a Differential Gear Ratio?
Whether you have a transaxle or a differential, every car has a differential gear ratio. This is sometimes referred to as the final drive ratio. Torque needs to be transmitted from the engine to the drive wheels in order for the car to be able to move. The transmission and axle housing, or differential, perform this transmission of torque, applying gear ratios in the process. The differential gear ratio describes how many time the small gear in the axle housing, called the pinion gear, which coupled to the drive shaft, turns. To make the output gear, (the ring gear,) turn a single time. This gear reduction allows all of the engine torque to be used efficiently.
For more info, see The Pros and Cons of Installing 4.10 Gears