Differentials – What They Do

Differentials – What They Do

One of the finest inventions in the automobile industry- the differential. What does it do? Let’s have a look.

The differential is a component widely used in rear-wheel drive, four wheel drive and all-wheel drive vehicle setups. To understand its concept, let’s imagine a circular running track with 2 lanes. The inner lane is shorter compared to the outer lane due to difference in its distance from the centre (radius). If 2 athletes, A & B, were to race on the inside and outside lanes (respectively) in the clockwise direction, A would easily win. B would have to run a lot faster to even keep up with A because A has to run in a smaller circle compared to B. Right?

 Now replace these athletes with the right wheels (A) and left wheels (B) of a vehicle connected to each other via a solid shaft turning with the centre of the circle as its reference. Due to the connection via solid shaft, both A & B will rotate at the same speed. But they need to rotate at different speeds because of their different radii. Since they can’t rotate at different speeds, one tyre will cause the other tyre to slide/drag in its lane. Meaning a lot of tyre wear. The outer wheel (B) needs to rotate faster compared to the inner wheel (A) to run without slipping. This is where a differential comes into play. It allows both, the inner and outer wheels to rotate at different speeds so that tyre wear decreases.

Types of differentials:

  1. Open Differentials:

As its name suggests, an Open differential’s mechanism allows both wheels to rotate at different speeds relative to each other.

  1. Locking Differentials:

In a situation where one tyre of the vehicle is on a solid surface, while the other is in mud, the open differential sends more power to the tyre with lower resistance. Hence the differential keeps sending power only to the tyre in mud. The vehicle can’t move forward as the tyre in mud keeps spinning without traction and no power is being sent to the solid surface tyre. To get out of such a situation, locking differentials are used. When switched on by the driver, the differential locks the left and right tyres to each other (which is as good as having a solid shaft in place of the differential). This forces both wheels to move at the same speed. After locking the differential, both wheels (the one on solid surface and the one in mud) rotate and the vehicle is able to move forward. This type of differentials are used in four wheel drive setups to improve off-road capability.

  1. Limited Slip Differentials:

These are a mix between open and locking differentials. The differential can automatically open or lock as per the conditions of the terrain either mechanically or electrically.

  1. Torque vectoring differentials:

First let’s understand what torque vectoring means.

Let’s say that you’re taking a fast right turn. The weight of your vehicle shifts towards the left because of the centrifugal force. Pushing the vehicle’s limit on this turn will cause the tyres on the left side to start losing grip and eventually slide off its path. The function of a torque vectoring system is to apply brakes on the inner right tyres (in this case) so that the outer left tyres can use them as a pivot point to turn at a higher speed. Thus increasing the overall cornering speed of a vehicle. So a torque vectoring differential considerably reduces the speed of the inner tyres making it a sharper handling vehicle.

Front wheel drive vehicles are the most widely used ones because of their less complex mechanisms. The power is being delivered to the front wheels and hence their rear wheels don’t need to be connected to each other. Since the rear wheels aren’t connected to each other, they are able to rotate at different speeds cancelling out the need of a differential. Engineers have also brought in torque vectoring into front wheel drive vehicles without using a torque vectoring differential by electronically applying brakes to the inner wheels in a turn.

Various types of differentials have been worked upon to increase usability, convenience and performance of vehicles. With the rise in electric fueled vehicles, technology has reached a stage where differentials are not needed at all. We already have seen electric vehicles with 4 motors, one for each wheel. In such vehicles, any amount of the total power can be delivered to any wheel or a combination of wheels. It can be setup as a front wheel drive one day, a rear wheel drive on the other day and an all wheel drive on the 3rd day. If electric vehicles are mass-used in the coming years, differentials might never have to be used again. And this might be a good thing.


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