Locking Differentials vs. Unlocked Differentials

Locking differentials might be better for off-roading

ARB, Air Locking Rear Differential

Richard Harvey/Wikimedia Commons/CC ASA 3.0U

When it comes to traction in off-road situations, differentials play a key role. Compared with a standard or open differential, a locking differential (also known as a diff lock, locker, or differential lock) improves traction. These are common in four-wheel drive (4WD) vehicles.

The locking differential limits the two wheels on an axle to rotate at the same speed. In essence, it locks them together as a unified shaft. Both wheels then turn together, regardless of whatever traction is available. With a locked differential, each wheel can apply as much spinning force as the traction will allow. This means the torques on each side will be unequal but have equal rotational speeds.

Unlocked Differentials

An unlocked, standard, or open differential means that each wheel can rotate at different speeds. This occurs when you turn and prevents tire scuffing. An open differential provides the same torque to each wheel on a single action. Even though the wheels can spin at different speeds with this type of differential, they receive the same force for the rotation, even if one is stationary and the other is moving.

Automobiles with standard four-wheel-drive, also known as all-wheel drive, have three differentials. One differential is on each of the two axles, and a central differential (known as a transfer case) lies between the front and rear axles.

Vehicles with a locked differential may be at a bigger advantage when it comes to traction compared to a vehicle with a standard or open differential, but only when the traction under each wheel is different. If you are a serious off-road driver, your vehicle probably has a locking differential. 

Types of Locking Differentials

There are three main types of locking differentials:

  • An automatic lock will lock and unlock automatically; the driver doesn't have to do anything. These make sure that the right amount of power always flows to both wheels regardless of the traction. They will then unlock when one wheel needs to spin faster when turning a corner. At rest, the position is locked. This type of differential increases wear on the tires.
  • A selectable lock puts the driver in control of turning the differential between lock and unlock modes. It can use either pneumatics (compressed air), electronic solenoids (electromagnetics), or a cable-operated mechanism to function. They are more complex and expensive than automatic locks. This type lets the differential perform in open mode for better drivability and maneuverability, but there are more parts involved that can fail.
  • Spools are devices that connect the axles and aren't featured in most consumer cars, only competitive driving vehicles.

It may sound as if locking differentials are the best option, but they have some disadvantages. There is more tire wear because they don't operate as smoothly as standard or open differentials, and they can make banging or clicking noises during locking and unlocking. If you're an off-roader, however, they may be just what you need.