A crown wheel and pinion are a pair of gears found in a drive wheel of a vehicle in which the pinion is at the end of the propeller shaft driving the crown wheel. The setup works when the pinion sets on top of the crown wheel. The pinion is substantially smaller than the crown wheel, and the teeth turn very quickly to produce forward motion.
In rear-wheel drive vehicles, the crown wheel and pinion is mounted on the differential of the back axle. Crown wheel and pinion gears are not found on wheels without a drive train attached. The heights of the gears must be set correctly or the vehicle will not move forward correctly.
These parts must be maintained properly if the wheels and tires are to function. The mating teeth of the pinion should be brushed clean after the gears are inspected. Crown wheel bolts can become fatigued if the axle is subjected to extreme motion such as offroading.
The arrangement of the crown wheel and pinion is known as a hypocycloid. One gear rolls internally along the circumference of another gear without slipping. The rapid motion of these gears drives machinery, or in this case, the wheels of a vehicle.