Getting started with Differential Gear

Here we all know that DIFFERENTIAL is an integral part of all four wheelers and wheels receive power from the engine via a drive shaft. The main function of the DIFFERENTIAL  is to allow these wheels to turn at different RPMs while receiving power from the engine.

Now consider the wheels which are negotiating a turn. It is clear that the left wheel has to travel more distance compared to the right wheel. This means left wheel has to rotate at higher speed. If these wheels are connected using a solid shaft, the wheels would have slipped to accomplish the turn. This is exactly where DIFFERENTIAL finds its place. The ingenious mechanism in a DIFFERENTIAL allows left and right wheels to turn at a different RPMs while transferring power to both the wheels.

And now we will learn how DIFFERENTIAL achieves this in a step by step manner, using its simple mechanism. If you have simple physics knowledge then you will understand it easily and certainly.



We all know that power from the engine is transferred to the RING gear through a PINION gear. The RING gear is connected to a SPIDER gear which is at the heart of differential. The SPIDER gear is free to make 2 kinds of rotation, 1st along with ring gear and 2ndon its own axis. SPIDER gear meshes with 2 side gears, so power from the engine flows from the pinion to the left and right wheels as described.


Now let us consider different possible cases:

CASE 1:  Vehicle moves straight [ N left = N right ]                                                                                   (N=RPMs)

In this case, spider gear rotates along with the ring gear but doesn’t rotate on its own axis. Spider gear will push and make the side gears turn and both will turn at same speed. [or] When the vehicle is moving straight, spider–side gear assembly will move as a single solid unit.


CASE 2: When vehicle is taking a right turn [ N left > N right ]

The spider gear plays a pivotal role here. Along with the rotation of ring gear, it rotates on its own axis. So spider gear is having a combined rotation. The effect of combined rotation on the side gear is interesting. When properly meshed side gear has to have some peripheral (auxiliary) velocity as that of spider gear. When spider gear is spinning as well as rotating, the peripheral velocity at the left side of the spider gear is the sum of spinning and rotational velocity. But at the right side, it is the difference (of the TWO ). Left side gear will have higher speed compared to the right side. This is the way how the DIFFERENTIAL manages to turn left & right wheels at different RPM.


CASE 3: Left turn [ N left < N right ]

The spider gear will spin in the opposite direction and right side gear will have higher speed compared to left side gear.

In order to carry the load, one more spider gear is usually added. A 4 spider gear arrangement is also used for heavy load vehicle. In double SPIDER  gear load mechanism the 2 spider gears will spin in opposite direction.

Apart from allowing wheels to rotate to rotate at different RPM, DIFFERENTIAL has got 2 more functions. 1st is speed reduction at pinion ring gear assembly due to higher gear ratio. 2ndfuction is to turn the power flow direction by 90 degrees.

So far what we have gone through is known as an open or standard differential.