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Locker

Car culture term

Locker
Photo: Richard Harvey / Wikimedia Commons · CC BY-SA 3.0

What is Locker?

A locking differential that mechanically or electronically locks both wheels on an axle to spin together. Used in off-road and drag racing applications.

Locker (locking differential) is a differential type that completely locks the two wheels on the same axle to rotate together at the same speed. Unlike an open differential or LSD, a locker does not allow any speed difference between left and right wheels when engaged. This provides maximum traction in low-grip conditions but causes tire scrub during normal cornering.

Locker types include automatic (engages when slip is detected, like the Detroit Locker), manual (driver-engaged via switch or lever, common in 4x4 trucks), electronic (computer-controlled engagement, common in modern off-road vehicles like the Wrangler Rubicon), and air (ARB Air Lockers, popular in dedicated off-road builds). Each has different characteristics suited to different use cases.

Lockers are essential for serious off-road driving (rock crawling, deep mud, technical trails) where one wheel may lift off the ground. Without a locker (or with an open differential), all torque goes to the unloaded wheel, killing forward progress. Lockers are also used in drag racing where launch traction is critical. They are not typically used in road driving because they cause noticeable handling effects in corners.

What are lockers?

Lockers, or locking differentials, force both wheels on an axle to turn at the same speed instead of spinning independently. That guarantees power to both wheels for off road traction or a straight line drag launch. On pavement a fully locked axle fights you in corners, so many street lockers can be switched off.

Related terms

LSD4WD

Frequently asked questions

Is a locker worse than an LSD on the street?
Yes, in normal driving. A locker causes tire scrub during cornering because the wheels cannot rotate at different speeds. This is felt as understeer in tight corners and tire wear on the inside wheel. LSDs allow some differential action and behave more naturally on the street. Lockers are typically used only when off-road or drag racing benefit outweighs street compromise.
Can I leave a locker engaged on the highway?
Manual lockers should be disengaged at higher speeds and during normal cornering. Automatic lockers (Detroit Locker) and electronic lockers are designed to disengage under load. Driving a manual locker on the highway in dry conditions is unsafe and accelerates wear.
What is an ARB locker?
ARB Air Lockers are a popular brand of pneumatically-engaged manual lockers used in off-road builds. Engagement is controlled by an air compressor and switch on the dashboard, allowing the driver to engage or disengage as needed. ARB lockers are widely used in serious off-road builds (overlanding, rock crawling).
Does the Wrangler Rubicon have a locker?
Yes. The Wrangler Rubicon has electronically engaged front and rear lockers as standard equipment. The driver can engage them via switches on the dashboard. The Rubicon is designed specifically for off-road use and the lockers are essential for the technical terrain it can handle.
Is a spool the same as a locker?
No. A spool eliminates the differential entirely; the two wheels are permanently locked together. A locker can be engaged or disengaged. Spools are used in drag racing where the car only needs to launch straight; they are unsuitable for any street or off-road use that involves cornering.
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