Proof Engineering has created this video to describe how a standard open differential works. All modern cars, whether front or rear wheel drive employ some form of differential. Simply put, the differential allows engine power to be divided among the driving wheels in varying proportions for cornering.
Driving Straight - Most of your time spent driving is in a straight line, but occasionally you need to turn. This is why a differential is useful. In this case, all four internal gears rotate with the ring gear. Notice one ring gear rotation equals two wheel rotations (one left, one right).
Turning -- Here we show the differential performing a left-handed corner. In a left turn, the outside or right wheel must travel a longer distance than the inside wheel. This differential gearing arrangement allows the ring gear's rotational velocity to be divided unequally between the wheels. One ring gear rotation still equals two wheel rotations. Left wheel = 1/4 revolution, right wheel = 1-3/4 revolutions, totaling to 2 revolutions.
Wheel Slip - For drivers that encounter snow and ice on a regular basis this video segment might look familiar. When one driven wheel is on pavement and the other is on a patch of ice the latter will spin freely while the vehicle stays at rest. Wheel slip is one drawback to the open differential mechanism. A limited slip differential (not shown) was later developed to solve this. One ring gear rotation still equals two wheel rotations. Left wheel = 0 revolutions, right wheel = 2 revolutions, totaling to 2 revolutions.
Rear Wheels Lifted Off Ground - If you were to raise your car so that both driven wheels are off the ground, these wheels will spin freely. But as you spin one wheel, the opposing wheel will counter-rotate, or rotate in the opposite direction. This will occur even with the transmission in PARK (or in-gear for a manual transmission); notice the driveshaft and ring gear do not move.
