• RWD, FWD, AWD or 4WD?

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    by Eric Peters: Holiday
    Roadblocks — WhatYouShouldKnow

     

     
     

    What’s
    the best set-up for winter-weather driving? Or just driving,
    generally?

    Is it rear-wheel-drive?
    Front-wheel-drive? All-wheel-drive? Or four-wheel-drive?

    Here are some
    of the the pros and cons of each:

    Four-wheel-drive
    (4WD)

    This system
    is typically found in pick-up trucks and truck-based SUVs. Most
    4WD systems work “part-time” – engine power goes
    only to the rear wheels until the driver (or, in the case of automatic
    systems, the onboard computer) engages the front axles. Typically,
    the power split front-to-rear is not adjustable. When in 4WD mode,
    the front wheels get 50 percent of the engine’s output and
    the rear wheels get the other 50 percent in a fixed-ratio split.
    Truck-based 4WD systems are also distinguished by the presence of
    a two-speed transfer case and 4WD Low range gearing, which is designed
    for very low-speed use in deep, unplowed snow (or off-road).

    The upside:
    Truck-type 4WD systems are great for dealing with very heavy snow
    on unplowed roads and for off-road driving on muddy, uneven terrain;
    the Low range gearing makes it possible to crawl up steep inclines
    and slog through deep mud. Truck-type 4WD is great – even essential
    – for people who live in very rural areas or who must deal
    with heavy snow on unplowed country roads.

    The downside:
    Truck-type 4WD systems usually operated in 2WD mode – with
    just the back wheels receiving engine power. When in 2WD mode, these
    vehicles often have less grip than a FWD car, which has the traction
    advantage of the drive wheels pulling (instead of pushing) the car
    and also because the weight of the engine and transmission are sitting
    on top of the driven wheels. In addition 4WD systems are not designed
    to aid high-speed handling/traction on dry, paved roads. In fact,
    most 4WD systems come with warnings not to engage the 4WD on dry
    paved roads, because it may negatively affect handling and result
    in premature wear of the components.

    Finally, a
    4WD system adds a lot of extra weight to the vehicle, which in turn
    cuts down on fuel economy. While you may only need 4WD a few days
    out of the year, you’ll be paying for it every day by lugging
    around a couple hundred pounds of additional dead weight.

    Not many people
    are aware of these significant everyday limitations of 4WD –
    even though the information is usually right there in the owner’s
    manual.

    The bottom
    line: Buy a 4WD if you need a vehicle with serious off-road
    capability or have to travel often on rural (and unpaved) gravel
    or dirt roads – or if you live in an area subject to severe
    winters where it’s routine to have to drive through heavy snow
    on unplowed roads. Otherwise, it’s probably a money-waster.

    Front-wheel-drive
    (FWD)

    Most passenger
    cars being built today are front-wheel-drive – including “crossovers”
    that look sort of like SUVs but which are (usually) built on a car-based,
    FWD chassis.

    The upside:
    FWD cars can actually be pretty tenacious in the snow because the
    weight of the engine/transaxle is sitting right on top of the drive
    wheels. FWD is vastly better in the snow than a rear-wheel-drive
    car. With a good set of all-season or snow tires, you will probably
    be able to make it to work unless the snow is really deep –
    in which case it’s the absence of ground clearance more than
    anything else that will cause you to get stuck. FWD is also more
    economical – both to buy “up front” and to operate
    over the life of the vehicle. You’re not paying extra when
    you buy the car – and you’re not paying every time you
    gas up to lug around equipment you only use a handful of times every
    year.

    The downside:
    FWD cars are weight-biased toward the front, which is a built-in
    design limitation as far as handling/performance is concerned. Also,
    the wheels that propel the car must also steer the car, which
    isn’t optimal for high-speed driving/cornering. This is why
    most race cars and also high-performance cars are rear-wheel-drive.
    FWD is fundamentally an economy-oriented drivetrain layout designed
    to cut down on vehicle weight, simplify assembly and reduce manufacturing
    costs.

    The bottom
    line: FWD is a good choice for the average driver who uses his
    vehicle to get from “a” to “b” and would like
    to have decent traction on those few days each winter when there’s
    some snow on the roads.

    All-wheel-drive
    (AWD)

    This is a system
    in which engine power can be sent to all four wheels – or even
    to individual wheels – as necessary to maintain traction. As
    recently as five or six years ago, only a few makes/models offered
    AWD systems; today, AWD is either standard or available optionally
    on many types of passenger cars, wagons, minivans and light-duty,
    car-based “crossovers.”

    The upside:
    AWD provides excellent all-year/all-weather grip on snow-covered
    roads in winter and improves handling on dry (or wet) paved roads
    in summer. Unlike a truck-style 4WD system, AWD is optimized as
    much for use on smooth, paved surfaces as it is for use in snow
    (or even on unpaved gravel and dirt). High-performance AWD-equipped
    sports cars and sedans offer incredible dry-weather, on-road handling
    with superior wintry weather capability. Also, AWD systems do not
    require any driver involvement; power is automatically routed to
    the wheels with the most traction. And they can kick as much as
    90-plus percent of the engine’s power to the front (or rear)
    wheels, as the traction situation dictates.

    The downside:
    AWD is not designed for off-road use; there is no two-speed transfer
    case or 4WD Low range gearing. AWD can also add substantially to
    the purchase price of the vehicle – sometimes by as much as
    several thousand dollars. In some cars, AWD also usually adds significant
    weight to the car, which cuts both performance and fuel economy.

    The bottom
    line: AWD is an excellent choice for the performance-minded
    driver who values dry-weather handling and high-speed grip in a
    corner as much as being able to get out of his driveway when it
    snows.

    Rear-wheel-drive
    (RWD)

    This was once
    the standard drivetrain layout of most passenger cars, especially
    domestic-brand models. The engine is up front – but power is
    sent to the rear wheels exclusively.

    The upside:
    Rear-drive cars spread the weight of the engine, transmission and
    axle assemblies front to rear more evenly than nose-heavy FWD cars
    – and tend to be lighter (and cheaper to buy/maintain) than
    AWD-equipped cars. Rear-drive cars are also rugged and durable –
    which is why they are favored for police use/taxi duty. And finally,
    rear-drive allows for smoky burnouts – important to many performance
    car fans.

    The downside:
    A RWD vehicle is not the hot ticket for snow driving – unless
    you enjoy fishtailing like a just-landed sea bass. Rear-drive (2WD)
    pick-ups are especially atrocious in snow; their light rear ends
    tend to break loose even on wet roads.

    The bottom
    line: If you enjoy a good burnout every now and then, live in
    an area where winters are mild – and can handle dealing with
    some hassle on those few days each year when it does snow –
    then rear-drive will probably work for you.

    Throw
    it in the Woods?

    November
    29, 2010

    Eric Peters
    [send him mail] is an
    automotive columnist and author of Automotive Atrocities and
    Road Hogs (2011). Visit his
    website
    .

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