Bonham field notes · Understand your vehicle
AWD and 4WD describe only part of the traction story.
A differential lets driven wheels accommodate different rotation speeds, such as when the vehicle turns. Open, limited-slip and locking designs manage that job differently. The important next question is which actual system a vehicle has and what its instructions allow.
Three categories, in plain language
Allows different wheel speeds
Open differential
The wheels can rotate at different speeds. Available traction at one side can limit the drive force the axle can use.
An open differential is not the same thing as a vehicle being two-wheel drive.
Limits slip between sides
Limited-slip differential
A limited-slip design can bias torque between the wheels while still allowing different speeds. The mechanism and its limits vary by design.
Limited-slip describes a category, not one identical system used in every vehicle.
Creates a locked axle condition
Locking differential
When locked, the two sides rotate together rather than freely accommodating different wheel speeds. Locking may be automatic or selectable, depending on the design.
Use the actual instructions for engagement, operating conditions and restrictions.
Begin with the turn, not the badge
The inside and outside wheels follow different paths through a turn. Allowing their rotation speeds to differ is part of why a differential exists. Traction conditions introduce another question: how does that particular design respond when the two sides do not have the same grip?
This is separate from whether a vehicle can drive one axle or both. A 4WD label does not identify every differential or its behavior. Keep the transfer-case or AWD-system description and the axle-equipment description on separate lines when comparing vehicles.
Limited-slip is not simply another word for locked
Eaton’s explanation distinguishes limited-slip designs that bias torque while allowing wheel-speed differences from designs that create a locked axle condition. Those are different mechanisms, not a simple better/best ladder.
How a system responds depends on its design and operating conditions. Electronic traction-control functions can also affect the overall vehicle response. Do not treat the presence of traction control, a dashboard icon or an appearance package as proof of a particular mechanical differential.
Automatic and selectable need different questions
Ask how the actual system engages and disengages and which instructions apply. An automatically acting design and a driver-selectable locker may have different operating requirements. Neither name provides a universal switch sequence, speed limit or surface recommendation.
This article gives no engagement procedure, retrofit instructions or off-road test. Follow the exact vehicle and equipment guidance. Do not create a hazardous wheel-spin situation to demonstrate a feature or assume that a locked axle improves every driving condition.
Verify equipment and present condition separately
For a candidate vehicle, use the applicable build or equipment information to identify the system. On a modified or used truck, ask about changes and relevant records. Factory configuration and present installed equipment may need separate verification.
If the feature matters to your use, obtain an appropriate explanation and qualified assessment of unresolved condition questions. No differential can establish a vehicle’s overall towing approval, tire suitability or ability to complete a route. These are traction-system categories, not a promise that a particular truck will avoid getting stuck.
Questions readers ask
Does every 4WD vehicle have locking differentials?
Do not assume so. Verify the actual axle and driveline equipment and the applicable instructions.
Can I choose solely from the differential label?
No. Consider the complete vehicle, intended use, tires, operating limits and current condition.
Keep learning
Related published guides: AWD vs. 4WD: Look Past the Badge · Buying a Modified Used Truck? Ask for the Build File. · Driver-Assistance Features: Verify What the Actual Vehicle Does.
Research behind this article
- Eaton — Limited Slip Differentials
- Eaton — Locking Differentials
- Applicable vehicle and differential owner instructions
By Bonham Chrysler · Prepared with AI assistance · Published November 2, 2026. Images and conceptual diagrams are qualified where shown. No hands-on test or technical certification is claimed.