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4WD

Car culture term

4WD
Photo: Unknown / Wikimedia Commons · CC BY-SA 3.0

What is 4WD?

4WD, or four-wheel drive, is traditionally a part-time, driver-selectable system on trucks and off-road vehicles that uses a transfer case with high and low range to send power to all four wheels.

Four-wheel drive, or 4WD, traditionally refers to a part-time system found on body-on-frame trucks and dedicated off-road vehicles. In its normal driving mode, power goes only to the rear wheels, and the driver manually engages a transfer case to route power to the front axle as well when extra traction is needed, such as on gravel, mud, sand, or snow. The transfer case typically offers a high range for slippery but reasonably fast driving and a low range that multiplies torque significantly for slow, technical off-road work like rock crawling or steep grades. Many 4WD systems also include locking differentials that force both wheels on an axle to spin at the same speed for maximum traction in extreme conditions.

Engaging 4WD is usually described by drive mode: 2H is rear-wheel drive only, 4H locks the front and rear driveshafts together for four-wheel traction at normal speeds, and 4L does the same but through a lower gear reduction for maximum torque at low speed. Because 4H mechanically locks the front and rear axles to spin at the same average speed, it should not be used on dry pavement. Turning a corner requires the front and rear wheels to travel different distances, and on high-grip dry asphalt the driveline cannot slip enough to accommodate that difference, causing binding, drivetrain stress, and unpredictable handling, sometimes called wind-up.

4WD differs from all-wheel drive (AWD) in both intent and mechanism. Classic part-time 4WD is built for maximum low-speed torque and traction in off-road conditions and generally must be manually switched on and off. Full-time AWD systems, by contrast, are designed to operate continuously on any surface, including dry pavement, using a center differential, viscous coupling, or electronic clutch pack that allows front and rear wheels to rotate at different speeds. Some modern trucks blur this line with an "auto 4WD" mode that behaves more like AWD, but traditional 4WD remains fundamentally a part-time, off-road-oriented system.

Related terms

AWDLockerBody-on-frameOverlanding

Frequently asked questions

What is the difference between 4H and 4L?
4H engages four-wheel drive at a normal gear ratio for driving at regular speeds on loose or slippery surfaces. 4L engages the same four-wheel drive but through a lower gear reduction in the transfer case, multiplying torque for slow, technical situations like rock crawling, steep inclines, or towing out of mud.
Why can't you drive in 4WD on dry pavement?
Engaging 4H or 4L locks the front and rear driveshafts to turn at the same average speed. Since the front and rear wheels need to travel different distances in a turn, dry pavement's high grip prevents the driveline from slipping enough to compensate, causing binding and stress on the axles and transfer case.
What is a locking differential and how does it relate to 4WD?
A locking differential forces both wheels on the same axle to spin at identical speed, ensuring power reaches a wheel with traction even if the other wheel is completely off the ground. Many dedicated off-road 4WD vehicles offer front and/or rear locking differentials in addition to the transfer case.
Is 4WD the same as AWD?
No. Traditional 4WD is part-time and manually engaged, built around a transfer case for off-road torque, and generally unsuitable for dry pavement use in 4H or 4L. AWD is designed to run full-time on any surface, using a center differential or clutch system that allows front and rear wheels to rotate at different speeds automatically.
What does "auto 4WD" mode mean on modern trucks?
Auto 4WD is a mode on many modern trucks and SUVs that automatically varies torque between front and rear axles as needed, similar to AWD, without the driver manually locking the transfer case. It offers more everyday flexibility but is generally still a separate setting from dedicated 4H or 4L off-road modes.
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