We hear or see the terms all the time: front-wheel drive (FWD), rear-wheel drive (RWD), four-wheel drive (4WD) and the newest type, all-wheel drive (AWD). But what are they? How do they differ? And how come 4WD, in its AWD form, is on so many new cars today (see box)?
Vehicles with two powered wheels (2WD) are either RWD or FWD. The former pushes the vehicle, the latter pulls it. (Two-wheel drive also describes vehicles with 4WD when that capability isn't active.)
FWD is now in about 70 percent of new cars for three reasons. Compared to RWD cars, front-drive models get better mileage (more efficient, less vehicle weight), eliminate interior floor "humps" (caused by transmissions and drive shafts) and cost less to make. FWD vehicles generally drive more easily and also get better traction because engine weight sits over the drive wheels.
Now mostly in pickups, truck-based SUVs, luxury cars and sports cars, RWD has arguments to make as well. Rear-drive vehicles can tow more and they corner and handle better in dry conditions. That's because steering and power functions are separate, allowing front wheels to turn more, and vehicle weight to be more evenly distributed. RWD cars accelerate better than FWD cars because more weight shifts to the rear in acceleration. RWD is also cheaper to repair and maintain, partly because there's less weight wearing out front tires and brakes. Though offering less traction on snow/ice/gravel, RWD vehicles steer more predictably in such situations because front wheels maintain some traction when rear wheels slip.
Four-wheel drive vehicles, aka 4x4s, were once almost exclusively trucks or off-road vehicles. Today, the term 4WD refers to vehicles that allow drivers to switch into 4WD by deliberately engaging the second set of wheels. These vehicles usually have three settings: 2WD and low and high 4WD. Low provides more torque for pulling power and off-road climbing. High is for better traction in slick conditions.
AWD, which can't be disengaged by a driver, has no low or high settings and lacks a transfer case, eliminating any gearing down for heavy work. AWD systems automatically shift power to non-drive wheels when sensors detect drive-wheel slippage. 4WD is mostly a truck/SUV term; AWD usually refers to cars, crossovers, wagons and minivans.
A shift has occurred over the past few years in which a greater demand has emerged for AWD sedans. These cars provide year-round traction in rain, mud, snow and ice, especially when AWD is teamed with ABS, traction control, anti-roll technology and electronic stability control. But there's a tradeoff. AWD and 4WD reduce mileage and add complexity and cost to vehicles.
2008 Cars with AWD
