Jerry, Harrisburg, Pa.

Answered by Cars.com senior editor Joe Wiesenfelder:

This question helps clarify what all-wheel drive and other four-wheel-drive systems do, and that is to help you accelerate and keep moving on slick surfaces. Technically, that’s all they’re intended to do. If you spin your drive wheels, especially when turning, you tend to slide sideways, so there’s an added benefit. All-wheel drive’s job is to transfer power (actually torque) from the wheel or wheels with the least traction to a wheel that has more traction, and that keeps wheelspin to a minimum. (Traction control accomplishes a similar effect with two-wheel drive, but it’s always helpful when more wheels can help push.)

Four-wheel drive adds weight to a car, so theoretically it will extend stopping distances. More mass means more inertia, and that takes more friction to stop. All other factors being equal – same model, same tires, same everything except the drive system – the one with four-wheel drive probably won’t stop as short or corner as well on dry, wet or icy pavement. But you can’t ignore that the added weight also presses down more on the tires, which can help offset the shortcoming. It’s on loose snow where additional weight might actually help, by causing the tires to dig down deeper and gain traction. This is why we used to put sandbags in the trunks of rear-wheel-drive cars before the days of traction control. In the big picture, though, all-wheel drive doesn’t improve braking, and it can degrade it.

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Answered by Joe Bruzek on January 8, 2009 in How Safe is This Car? , I'm Just Wondering , What Does This Mean? | Permalink

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