It can help get you going and keep you moving through mud, sand, and other loose surfaces. Most AWD systems deliver power primarily to one set of wheels, front or rear. When slippage is detected at one axle, power is diverted to the other axle, in hopes of finding more traction there. Sophisticated clutch systems and, more recently, the use of electric motors allow for precise control over the power sent to each wheel.
High-performance vehicles with AWD often send power to each corner at all times but can alter the balance among the wheels depending on conditions or drive mode to change the performance characteristics of the car.
Not all AWD systems are equal. Many other systems fitted to front-wheel-drive vehicles operate with percent of the power normally going to the front wheels; the rear wheels then receive power only when the front wheels start slipping, or proactively based on the vehicle conditions or drive mode selection. This transfer of power is traditionally achieved with a mechanical driveshaft running the length of the car, but electric vehicles and some hybrids utilize individual motors at each axle with no physical connection between them.
AWD systems are especially helpful in rapidly changing conditions or when driving on a road with intermittent snow and ice. It is commonly used for car-based SUVs, as well as certain cars and minivans. Although four-wheel drive 4WD and AWD are designations that are often used interchangeably in advertising and sales literature, there is a difference. Generally, 4WD is optimized for severe off-road driving situations such as climbing over boulders, fording deep water, and tackling steep hills with loose, low-traction surfaces.
Most 4WD systems use a heavy-duty transfer case with a high and a low gear range, the latter used to increase torque at the wheels for low-speed climbing. Some have differentials which allow left and right wheels and front and rear axles to turn at different speeds that can be locked for maximum traction.
Modern 4WD systems are full-time, which means they stay engaged; automatic, where the vehicle automatically switches between two- and four-wheel-drive mode; or part-time, which requires the driver to manually shift between two- and four-wheel drive.
Aside from serious off-road enthusiasts, most drivers never come close to needing the capability that 4WD systems provide over and above AWD systems. Photo: Ford Photo: Ford. For rain and very light snow, 2WD will probably work fine, and for most vehicles, front-wheel drive is the preferred setup and is likely to cost less than an equivalent AWD model.
AWD is fine for most normal snow conditions or for light-duty, off-pavement excursions on dirt roads or slippery surfaces. Keep in mind that both AWD and 4WD systems add considerable weight to a vehicle, compromising fuel economy.
One of the reasons many people buy a traditional sport-utility vehicle is for the extra security and traction of four-wheel drive. Though having power delivered to all four wheels increases straight-line traction, it does nothing to improve braking, and most systems have little to no effect on cornering. Drivers can be fooled into traveling too quickly in slippery conditions with an AWD or 4WD vehicle, only to discover they are going far too fast when trying to stop.
With an all-wheel drive like that found in Subaru models, 20 percent of the engine's power is distributed to the rear wheels at all times. Other systems send percent of the power to the front wheels, only powering the rear wheels when there is slippage. As with two-wheel drive vehicles, there are advantages and disadvantages to four-wheel drive vehicles. The advantages include:.
In some situations, a good set of tires matters more than the vehicle's drivetrain. For example, snow tires assist you with stopping and turning on winter roads, something the drivetrain doesn't help you with. Consider where you live and the type of driving you do when choosing between two-wheel and four-wheel drive vehicles. New Cars. Buyer's Guide. Type keyword s to search.
Today's Top Stories. Future Cars Worth Waiting For: — Cavan Images Getty Images. Different Car Drivetrains The drivetrain, which sends power to the car's wheels, can make a significant difference in how the vehicle handles in rain and snow or on unpaved roads.
Pros and Cons of Two-Wheel Drive Two-wheel drive vehicles come in either front-wheel or rear-wheel configurations. The pros include the following: Two-wheel drive vehicles are less expensive than four-wheel drive models.
Two-wheel drive vehicles use less energy to power the wheels, so they are more fuel-efficient. Two-wheel drive vehicles are lighter, so they are more agile. Cons include: Two-wheel drive vehicles give you less power than four-wheel drive models. Two-wheel drive vehicles are not suitable for all terrains. Rear-Wheel Drive Configurations Consumer Reports notes that pickup trucks, SUVs on truck bases, sports cars, high-performance cars, and high-end sedans feature rear-wheel drive systems.
Four-Wheel Drive vs. All-Wheel Drive Four-wheel drive systems , according to Economical, often feature in pickup trucks and other vehicles used for off-road excursions. Four-wheel drive systems are set up to operate in one of three modes, including: Full-Time: All four wheels are permanently engaged. Part-Time: The driver can manually switch between two-wheel and four-wheel drive, depending on driving conditions. Automatic: The vehicle monitors road conditions and switches automatically from two-wheel to front-wheel drive as needed.
Pros and Cons of Four-Wheel Drive Systems As with two-wheel drive vehicles, there are advantages and disadvantages to four-wheel drive vehicles. As a rule they are faster in a straight line as well as round the corners - this is because the increased grip allows the use of a more powerful motor which easily overcomes any slight difference in efficiency. Typically I find I'm a lap or so faster with 14 laps being typical in a race running a 4wd than a 2wd.
The pan car is much lighter, and has a far simpler basically direct drivetrain. Pan cars are much harder to control, but are insanely fast if you can handle them. When grip is good on carpet say a good driver with a pan car can go faster than the equivalent with a TC. You can post now and register later. If you have an account, sign in now to post with your account.
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