A rear wheel drive vehicle converts the back-and-forth motion of pistons into the rotary motion of the vehicle's rear wheels. The ring and pinion is a big factor in effecting this transformation. Numbers inscribed on these devices give information that relate specifically to its function.
The pinion is a small rod with a slanted gear at one end. It rotates whenever the crankshaft rotates. The pinion gear meshes with the larger ring gear, which imparts rotary motion to the car's rear axle and rear wheels. Other associated gears allow the two rear wheels to rotate at different speeds when turning a corner.
Manufacturers often stamp rings and pinions with some numbers that help mechanics install them correctly, and others that identify the part and give the month and day of manufacture. Other numbers may give the number of pinion gear teeth, the number of ring gear teeth and the final drive ratio, which is the number of times the drive shaft has to turn before the axle shaft turns once.
With the engine running at the same speed, a final drive ratio of around 4.88 will turn the axle with greater force than a lower final drive ratio of around 3.70. The higher final drive ratio, however, will result in a greater expenditure of fuel.
