What Is & How Does A Differential Work?

Differentials - The Basics

What Is A Differential?

a fully labeled illustration of a vehicles engine gearbox and differential layout highlighting the differentials position within a modern rear wheel drive vehicle

The differential has a hard life, it rotates the outside driven wheel on your vehicle faster than the inside driven wheel to improve the cornering and performance of your vehicle whilst maintaining your tyre’s maximum usable life. During this process torque is transferred from the center prop shaft, through 90 degrees to the drive shafts that turn the vehicles wheels. Although durable, maintenance may be necessary.

The Differential’s 3 Jobs

To aim the engines power and torque at the vehicles driven wheels usually through 90 degrees.
To act as the final gear reduction in the vehicle, slowing the rotational speed of the transmission one final time before it is transferred to the vehicles wheels via the prop or drive shafts.
To transmit the engine power and torque to the road wheels while allowing them to rotate at different speeds to minimise tyre wear. This is the one that earned the differential its name.

How A Differential Works

Wheels Spin At Different Speeds!

You probably never considered your vehicles wheels sometimes need to spin at different speeds.

All The Same Speed

illustration of a vehicle driving and leaving behind 4 different color trails from its wheels to highlight how vehicle wheels rotate at the same speed when a vehicle drives in a straight line

When traveling in a straight line in a modern vehicle with 4 wheels they all turn at the same speed.

Different Speeds

illustration of a vehicle driving and leaving behind 4 different color trails from its wheels to highlight how vehicle wheels rotate at different speeds when a vehicle corners

It’s when you turn a corner that your driven wheels need to turn at different speeds. The outside driven wheel has to rotate more than the inner driven wheel as it has more distance to cover. Also in slippery conditions like snow or oil on the road one or both of your vehicles wheels may loose traction.

Why Do I Need A Differential?

If your vehicle had to be designed without a differential the driven wheels would have to be locked together. Now the driven wheels are forced to always turn at exactly the same speed you will find just turning a corner difficult. You would have to accelerate enough to make at least the inner wheel slip just to get round the bend. The most likely outcome would be skidding off the road. Also the extra stresses of the tyre scrubbing and skidding would be transmitted through the drive shafts and bearings causing extreme premature wear. The tyres would wear prematurely and possibly shred.

Vehicle Path Without A Differential

illustration of a vehicle driving and leaving behind 4 different color trails from its wheels to highlight how a vehicles non driven wheels rotate independently regardless of the vehicle direction of travel

The front wheels (red & blue) on our rear wheel drive illustration are not driven. They can spin freely and independently of each other at different speeds so there are no problems with cornering or tricky road surfaces here unlike the rear wheels.

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