Explainer

A differential exists to let wheels on an axle turn at different speeds. How it decides where to send torque separates the three common types.

Open

The default. Allows unlimited speed difference between wheels, ideal on pavement and useless when one wheel loses grip.

Torque follows the path of least resistance, so a wheel in the air or on ice receives the power while the wheel with traction receives almost none. One lifted wheel can stop the vehicle entirely.

Limited-slip

Adds a mechanism — clutch packs, gears, or a viscous coupling — that resists large speed differences and transfers some torque to the wheel with more grip.

A partial solution and a good compromise for mixed use: automatic, acceptable on pavement, and it will still give up if the difference is extreme.

Clutch-type units wear, and their behaviour degrades gradually enough that owners often do not notice until it is largely gone.

Locking

Mechanically locks both wheels on an axle to turn at the same speed. Traction at one wheel drives both.

Selectable lockers engage on command — open when you want open, locked when you need locked.

Automatic lockers engage under load and unlock when cornering. No input required, and capable of unpredictable handling on wet pavement.

A locked axle should not be engaged on high-traction surfaces, for the same reason part-time 4WD should not be: the speed difference a corner demands has nowhere to go.

How these stack

Open front and rear with 4WD engaged still leaves you dependent on one wheel per axle. A rear locker with an open front is a substantial improvement. Both locked is close to the maximum mechanical traction a vehicle can produce.

Traction control complicates this usefully — many systems brake a spinning wheel to force torque across an open differential, approximating a limited-slip effect. It works, and it generates heat, so it is a short-duration measure rather than a substitute.

This article was researched and drafted with the assistance of AI tools and reviewed, fact-checked and edited by Leonidas Clark before publication. General information, not advice for a specific vehicle.