What's Best On Snow And Ice: Four-Wheel Drive Versus All-Wheel Drive |
What's Best On Snow And Ice: Four-Wheel Drive Versus All-Wheel Drive
-- Jim Gorzelany, Forbes.com
With shoppers flocking to new-car dealers’ at rates not seen since the onset of the Great Recession, and at the most bone-chilling and snow-ridden time of the year, we’d bet many of them are taking a closer look at cars and trucks that fare best under extreme climactic conditions. But what kind of vehicle should a weather-besieged car buyer choose?
Aside from the front-drive setup typically found in most mainstream cars and the rear-drive layout many sports and luxury cars employ, nearly a third of all vehicles sold in the U.S. now offer either all-wheel drive (AWD) or four-wheel drive (4WD) as traction-enhancing alternatives. Which configuration is best for a given motorist depends on any number of factors, none the least of which involves just how severe conditions can become when Old Man Winter is behaving badly.
But before you head out to a showroom to kick the tires, be aware that any motorist can improve his or her existing vehicle’s abilities under adverse conditions simply by changing the tires. Those who own a sporty car equipped with low-profile performance tires, should switch to all-season rubber for the winter. Drivers in snowbound areas may want to install snow tires, which feature large, deep tread blocks to provide the greatest traction over loose surfaces. Tests have shown that front-wheel-drive cars fitted with snow tires can outperform an equivalent AWD car with all-season tires under severe winter circumstances.
Rear-drive, front-drive, all-wheel drive or four wheel drive – which is best depends on where you live, how bad the winters are and the type of vehicle you prefer to drive. Photo by Jim Gorzelany.
Rear-drive, front-drive, all-wheel drive or four wheel drive – which is best depends on where you live, how bad the winters are and the type of vehicle you prefer to drive. Photo by Jim Gorzelany.
At any rate, here’s a quick rundown of the various manners in which today’s vehicles put their power to the pavement:
Front-wheel drive. This is the standard configuration found on most cars and car-based crossover sport-utility vehicles. It became popular in the 1980’s as stricter fuel economy regulations dictated building smaller and more efficient vehicles. Front-wheel drive maximizes passenger room, as its forward transaxle configuration eliminates the “hump” running through a vehicle’s interior that housed the driveshaft connecting the engine to the rear wheels. Generally, front-drive cars tend to fare better in wet and snowy conditions than do rear-drive models, simply because they place more weight at the front of the vehicle directly over the drive wheels.
Pulling, rather than pushing a car also more effectively helps dislodge a car from the snow and negates a rear-wheel-drive vehicle’s tendency to lose traction when entering a curve too quickly. Basic front-drive should suffice for most city and suburban dwellers facing moderate winter conditions. Unfortunately, front-drive vehicles tend not to fare well when fitted with larger-displacement engines because of the phenomenon known as torque steer, which tends to pull a front-drive vehicle to one side under heavy acceleration.
Rear-wheel drive. Auto enthusiasts have long preferred the traditional front engine/rear differential layout, which affords a better front-to-rear weight balance and in turn tends to deliver superior ride and handling abilities. The advent of modern chassis systems (including antilock brakes, traction control and stability control) combined with improved tire technology helps compensate for – though doesn’t entirely eliminate – a rear-drive car’s inherent tendency to fishtail on slick surfaces and experience sudden “oversteer” in extreme handling situations. Those who endure a wintry climate may still need a hand pushing a rear-drive vehicle out of a snowbound parking space. To that end, a growing number of rear-drive models now offer optional all-wheel drive systems to help make them more accommodating winter vehicles.
Four-wheel drive. Before the SUV boom exploded in the 1990’s, most sport-utility vehicles were referred to as “4x4s,” by virtue of four-wheel-drive systems that imbued them with nearly superhuman off-road abilities. Back then you had to get out of the truck and manually “lock” the front wheel hubs to send power to all four corners, however. Today’s 4WD systems are much more sophisticated and come in several varieties, each of which is skewed more toward either off- or on-road use. Generally, models that offer 4WD are otherwise rear-drive vehicles.
Part-time 4WD is still offered on a handful of models like the Nissan Frontier pickup and Jeep Wrangler SUV. Typically the most-basic and least expensive type of 4WD system, the engine powers only the rear axle until the driver pushes a button or shifts a lever to additionally engage the front wheels. Full-time 4WD is likewise offered on many pickups and truck-based SUVs; it allows a driver to choose between rear-drive, 4WD and a safety minded “automatic” mode that engages the front wheels as needed when sensors detect wheel slippage. Permanent 4WD includes the aforementioned automatic system, but offers no two-wheel-drive option. To some degree all wheels receive power at all times.
Generally, all types of four-wheel drive systems include “low range” gearing for times when maximum traction is needed, such as getting out of the deepest snow drifts or mud ruts, which makes it the ideal configuration for those living in remote and/or snow-packed areas. It’s also best for those who traverse steep unpaved hills and engage in extreme off-road adventures.
It is important to note, however, that while 4WD helps you “go in the snow,” and may afford a bit of extra grip in low-traction situations over ice, it does little to aid a vehicle’s cornering abilities and virtually nothing for braking.
All-wheel drive. Available in many passenger cars, virtually all car-based crossover sport-utility vehicles, a few truck-based SUVs and one minivan (the Toyota Sienna), AWD is similar to permanent four-wheel-drive, sending additional power to the front or rear wheels as necessary to maintain traction over wet or snowy roads. Those living in snowier and/or more remote areas will want to choose an AWD car, particularly if the alternative is a less traction-friendly rear-drive configuration. AWD crossovers feature additional ground clearance that enables them to traverse deeply snow-packed roads or driveways without unduly scraping the undercarriage or otherwise becoming stuck.
Some AWD systems are also engineered to improve a vehicle’s handling abilities on dry pavement, with some able to send additional power to one to more outside wheels as needed in a torque-vectoring array for quicker cornering. However, as with 4WD, all-wheel-drive does little to keep a vehicle on track if it’s careening through an icy or snow-encrusted curve too quickly. Under normal circumstances some AWD systems will ordinarily send 100 percent of the engine’s power to the front wheels, while others will split the difference between front and rear on a 50/50 basis. Many higher-performance and luxury cars fitted with AWD will ordinarily shift more power to the rear wheels to maintain a sportier rear-drive feel. Unlike 4WD, however, AWD does not come with low range gearing, which means the system isn’t intended for hearty off-road use.
A few of the latest SUVs, particularly the Ford Explorer, Jeep Grand Cherokee and various Land Rover models, offer a so-called terrain management system that allows the driver to optimize the vehicle’s performance to maximize traction according to separate modes. Engaged via a center console dial, such systems typically include settings for normal pavement, snow, sand, and mud/ruts.
The Fine Print: Keep in mind that no matter with which drive system a given car or truck is equipped, there’s no violating the laws of physics. Driving all four wheels might make a vehicle go faster on wet on snowy pavement, but even the beefiest 4WD trucks can spin out of control on a patch of ice or through a slick curve if driven without regard to conditions. Always slow down as the weather worsens. Leave extra room between your vehicle and the traffic ahead – a car’s brakes won’t work as well as they would on dry pavement. And keep an eye out for frozen patches, especially on bridges and overpasses which tend to freeze sooner than paved roads.
If you do hit a slippery spot and the vehicle begins to skid, stay calm and steer in the direction you want to go, maintaining a light and steady foot on the accelerator. Slamming on the brakes is usually counter-productive when a car or truck is sliding sideways. If you’re coming to a stop in straight line and feel the brake pedal pulsating or chattering (and/or the “ABS” light is flashing on the instrument panel), this means the antilock function is activated. Do not let up on the brakes should this occur – maintain a firm foot on the pedal until the vehicle comes to a stop. And if the stability control warning light flashes on the dashboard, meaning the system is engaging to help counter wheel spin, interpret it as a signal to slow down.
As always, safety first.
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