Lockers & Differentials

The Difference Between Open And Locked Diffs

ARB, Air Locking Rear Differential
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. In general, the differential in a vehicle's axle allows the outer wheel to rotate more quickly when the vehicle turns a corner. The outer wheel travels about 30 feet farther than the inner wheel in a 360-degree turn. A 4WD vehicle has one diff in each axle.

A full-time 4WD vehicle also has a center-diff in the transfer case, because the front wheels rotate more quickly than the rear ones when turning a corner and traveling forward.


A Differential Always:

  • distributes equal amounts of torque to both wheels
  • reacts to resistance/traction to allow a wheel with more resistance to rotate less and a wheel with less resistance to rotate more (The rpm difference created by the differential is always proportional. If the inside tire rotates 15 rpm less in a turn than going straight - then the outside tire will rotate 15 rpm more than going straight.)

Locking the Differential Is Accomplished by Doing One of Three Things:

  1. Installing an open differential
  2. Installing a locking center section which ALWAYS locks the differential
  3. Installing a "lock-on-demand" unit like an ARB air locker

The trick is knowing when to lock the diffs and when not to.

What Happens When Irregular Terrain Leaves a Tire in the Air or on a Poor Traction Surface and You Have:

  • Open differentials
  • Locked differentials
  • Limited slip differentials