4x4

A 4x4 is a vehicle with four wheels, all of which can receive engine power simultaneously through separate axles. The first number denotes total wheels; the second denotes driven wheels. This differs from a 4x2 (conventional car), where only the front or rear pair receives power, and from a 6x4 or 6x6 truck, where multiple axles handle heavier loads.

The drivetrain uses a transfer case to split torque between front and rear axles, typically engaging via a mechanical lever or electronic switch. Most 4x4 vehicles include a differential lock or limited-slip differential on each axle to prevent wheel spin when one tire loses grip. High-range gearing suits normal roads; low-range provides mechanical advantage for climbing or descending steep terrain at controlled speed, reducing brake wear.

Variants exist across vehicle classes. Compact 4x4s and SUVs weigh 1500 to 2500 kg and carry passengers. Medium utility vehicles run 2500 to 4500 kg. Heavy-duty 4x4 trucks exceed 4500 kg and often feature live axles and coil springs for load carrying. Some models offer selectable 4x4 (driver engages it manually); others run permanent all-wheel drive, sending power to all wheels continuously but with variable torque distribution.

The term originated in military vehicle specifications during the 1940s. A Willys MB or similar machine marked 4x4 meant four wheels, four driven. The naming convention persisted and became standard marketing terminology, though technically redundant since any modern four-wheel vehicle is a 4x4 if it has all-wheel drive.

Common failure points include transfer case seals (which leak fluid under prolonged 4x4 engagement), worn differential gears from sustained off-road use, and hub locking mechanisms that stick from corrosion. Fuel consumption increases 10 to 30 percent in 4x4 mode due to higher drivetrain friction and engine load, so drivers typically engage it only on low-traction surfaces.