Two-wheel, four-wheel or nine-and-a-half wheels; if it's on the ground, man has somehow figured out a way to route power to it. There is no single best, as the ideal depends on what you're looking for in terms of performance. Rally-racer or rock-crawler, gas-sipper or freeway-flier, dozens of different drivetrain permutations await those seeking to optimize their driving experience.
Two Wheel Drive
Two-wheel drive -- aka "4x2," for four wheels, two driven -- comes in two basic variations, either front- or rear-wheel drive. FWD is fine if all you're looking for is to get from point to point in relative comfort and efficiency, but asking the front wheels to handle both acceleration and steering duties is a recipe for understeer. This phenomena happens when the front wheels lose traction before the rears, causing the car to "plow" through a turn instead of rotating and turning as it should.
Forget the marketing hype: if it doesn't have a locking transfer case, it isn't four-wheel drive -- aka "4x4," for four wheels, four driven. A transfer case works something like a manual transmission, with one shaft running straight through the case and powering the rear axle and another parallel shaft powering the front axle. Upon engaging 4WD, a mechanism -- either chain or gear drive -- locks the shafts together, splitting the power at a constant 50/50 front to rear. True 4WD can be part-time -- aka "manual," where the driver has to engage the transfer case -- or full-time, where the case engages automatically whenever the truck isn't turning.
An all-wheel-drive system differs from a true 4WD system in that it uses a center differential instead of a transfer case. Like the differential in the axles, the center differential allows the front and rear axles to turn at different speeds so the vehicle can turn corners more easily. Most modern AWD cars use a viscous-coupling center differential, which can vary the front-to-rear torque split to send power to the axle that has the most traction. One drawback to AWD is that the non-default axle tends to absorb some power even when not in use, which results in a slight drop in fuel economy and top speed.
AWD System Differences
All AWD systems aren't created equally. The most basic difference involves the "default" axle, or the one that gets full power whenever the other one doesn't need it. Power generally defaults to the rear axle if the engine sits longitudinally (front-to-back) and to the front if it sits laterally (sideways) in the chassis. This can make a huge difference in handling, as a rear-default car will generally handle more like a rear-wheel-drive car and a front-default will generally handle more like a front-driver.
Go for true 4WD if you're doing any kind of hard-core off-roading like rock-crawling or mud-bogging, as a viscous-coupling center differential's gooey fluid can overheat and fail under sustained torque. Modern, computer-controlled AWD cars will almost always be faster around a racetrack or rally course than any equivalent vehicle with 2WD, but don't require as much skill or driver involvement as 2WD. Use a RWD car if you enjoy dancing with physics and powersliding.
- "Auto Fundamantals"; Martin Stockel; 2005
- "Race Car Engineering and Mechanics"; Paul Van Valkenburgh; 2004
- "Chassis Engineering"; Herb Adams; 1992
- Detroit Free Press: AWD vs. 4WD vs. 4x4
- iSee Cars: AWD vs Rear Wheel Drive vs Front Wheel Drive
- Photo Credit Stephen Dunn/Getty Images Sport/Getty Images
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