What Is a Differential?

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Unless you’re a real gearhead, most people don’t necessarily know what car parts like a differential are. Well, never fear. We’re here to lay it out for you.
With some help from Driving.ca, we’ll tell you everything you need to know about a differential’s functions and types.
Close-up of a wheel with red brakes.
A car’s differential plays a crucial role in how much power is given to each wheel.

What does a car’s differential actually do?

The principal purpose of a differential is to delegate the power and torque going from the engine to the wheels. Without a differential, each wheel would get the same amount of power, causing them to spin at the same speed. 
This is fine for forward movement, but for turning, wheels need to spin at different speeds, since the outer wheels are travelling farther and need to go faster to compensate for the turn.
The differential makes sure that the inner and outer wheels get the required amount of power to make an effective turn, the inner getting less and the outer getting more. This way, no one wheel is forced to spin in place with too much power.
This system works differently for cars with front-wheel, rear-wheel, four-wheel, or all-wheel drive. Not only does the set of gears that make up the differential go in different places under the car, but four- and all-wheel drive vehicles need an additional center differential or transfer case,

Types of differentials

  • Open differential
An open differential system is the most common differential, named so because the wheels are always powered independently of each other. 
In order to send power to the right wheels, the system senses the resistance levels on each wheel. The wheel with the most resistance gets the most power, and vice versa.
  • Limited-slip differential
A limited-slip differential uses a different method, measuring wheel traction rather than resistance. This differential measures the amount of traction each wheel has and correspondingly gives power to the wheel with the most traction. This means that if a wheel loses its traction, it doesn’t get needless extra power.
Limited-slip differentials are mainly used in performance vehicles, though, so they aren’t usually seen in everyday cars. Mechanical-clutch, active, viscous, and Torsen differential systems are all different forms of limited-slip differentials.
  • Locking differential
Finally, we have the locking differential. This type of differential is mainly used for off-roading vehicles because of its ability to “lock” the wheels, forcing them to spin at the same speed. 
In most situations, the differential allows separate amounts of torque to be sent to each wheel. The driver can then choose to lock the wheels when they choose, which helps when travelling over large obstacles like boulders.
Some of the more intense off-roading vehicles even have two locking differentials—one for the front and one for the back. This can give vehicles more control when driving over rough terrain.

How does AWD or FWD affect the differential?

The differentials in AWD of FWD vehicles are the same as any other, but these cars do need an extra differential. They also have either transfer cases or center differentials as well to help distribute the engine power to the wheels. 
If the car has a center differential, it will be just like a normal differential, and can be any type except a locking differential.

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