Here is an excerpt from an article that ran in our local newspaper that to my mind sums up the difference between AWD and four wheel drive. Some may find this enlightening. My personal experience has been that in deep snow on my 17 percent grade long driveway, I'll take four wheel drive over AWD.
With the first major winter storm of the year, television news coverage chronicling the event takes perverse delight in showing the effects on traffic. Along with shots of vehicles struggling up icy hills or being dug out of snow banks, there is invariably footage of some crumpled SUV or crossover in the ditch or on its roof. Is this simply a matter of motorists forgetting to drive to the weather and road conditions, or, especially for owners of these SUVs and crossovers, a misplaced confidence in the traction abilities of their vehicles?
“Sport- utility vehicles offer a marked improvement in tractive effort and handling in snow,” says Chrysler’s Raynard E. Durham, vehicle line executive of SUV vehicles, “but what people often forget is that stopping distance. In fact, it is very much compromised in the snow.
“Even with active chassis systems that keep the vehicle in a straight line when stopping in the snow, it still takes a much longer length of road compared to dry and wet conditions to bring the vehicle to a stop. People forget this simple fact their first time out in the snow.
And, no matter the type of drivetrain, it takes all vehicles longer to stop on snow- covered roads, which makes winter tires a must. Testing by the Ontario Ministry of Transportation of vehicle stopping distances from 50 kilometres an hour — on asphalt roads covered with three to five centimetres of compact snow — showed a four- wheel- drive SUV coming to a halt in 35.7 metres when fitted with winter tires. With all- season tires on, the stopping distance increased to 42.8 m. That can be the difference between a close call and a trip to the autobody shop — or hospital.
“Four- wheel- drive and all- wheeldrive vehicles always offer improved traction in unfavourable weather conditions over two- wheel- drive vehicles,” says Durham. “Two- wheel- drive vehicles are still much better than they were 10 to 20 years ago because, with new active chassis controls, even two- wheel- drive vehicles can apply traction to two tires instead of one in snow. The second best system for inclement weather is all- wheel- drive. Vehicles ( with AWD) can send torque to all four tires.
The best system for inclement weather is an actively controlled 4×4 vehicle. These vehicles can send an optimal amount of torque — based on demand — to the tires with the most traction.”
Vehicle Stability Assist ( VSA) systems, a combination of traction control and braking systems, help any vehicle maintain direction and stability by slowing down one or more wheels via the brakes. But it only works when the vehicle is in motion, says Honda’s Mori. “Traction control simply slows down power delivery so you can slowly roll forward rather than slipping the wheels when starting ( up). These systems on front- wheeldrive cars with snow tires will get you through most slippery conditions.
“All- wheel- drive adds another level of traction by sending power to the axle with the most grip. So, even if one of the axles is sitting on a slippery surface, it can divert power to the other, thereby getting you going. All- wheel- drive systems with VSA and snow tires would be the ult*mate … in slippery conditions.”
While the benefits of having traction at all four wheels are obvious, there are a couple of specific disadvantages, namely the added cost at purchase time, plus some penalty at the pumps. “You’ll notice that fuel consumption can go up when you have all four wheels reacting,” notes VW’s Squires.
Adds Mori: “Due to extra weight ( about 80 to 100 kilograms, depending on the type of AWD system), an all- wheel- drive- equipped vehicle will have some fuel consumption penalty compared to its two- wheel- drive cousin. Some all- wheel- drive systems constantly send some power to all four wheels and this also adds some load on the engine,” which increases fuel consumption.