February 23, 2013

All-wheel drive (AWD): not all it's cranked up to be.

Rain, sleet, snow: winter is here. As you're starting to feel like a nervous turtle painfully crawling down the road, you start to wonder whether you shouldn't be driving a car with all wheel drive. After all, they are advertised to have excellent traction, great for wintry conditions.

In an AWD vehicle, the engine delivers power to all four wheels. That, together with the more even weight distribution over all its wheels, is the secret of its good traction: if one of the wheels starts slipping, there are three other ones to pull the car forward. Very handy if you go off-road regularly: it helps you get through uneven terrain, and the occasional muddy creek. It gives you that macho feeling, that you're ready to take on anything: at least, that's what the ads say.

All-wheel drive does add a few thousand dollars to the purchase price, and repairs can be costly as well, because of the complexity of the drivetrain. And unless your drive to the grocery store goes through a serious body of flowing water, you probably don't need AWD. Even in rain and snow, a conservative driving style and good tires will get you a long way even in a car that doesn't have AWD.

The truth is that you get sold confidence, since the jury is still largely out on the measurable safety benefits. According to a recent article in the Wall Street Journal, "Even industry executives who are pushing all-wheel drive into more models say demand for it is driven as much by emotion as hard data."

Certainly, for sleety and snowy conditions, you're better off not having a car with rear wheel drive, which tends to lose traction more quickly, and has a disconcerting - and dangerous - tendency to fishtail.

Rear-wheel drive cars are very sturdy: handy if you tend to hit the curb as you go around the corner. They also give better handling because the power is applied to the rear wheels whereas the steering is done separately by the front wheels. It's the kind of "performance" that will give you an edge if you're racing. For going around town at 25 mph you might not need that.

Most consumer cars have front-wheel drive because they are more simple in the assembly and therefore less expensive to buy and maintain. Front-wheel drive also gives better fuel efficiency. It makes a car nose-heavy, which is not a problem for everyday driving, and actually helps you keep traction in snowy conditions.

They are less rugged than rear-wheel or all-wheel drive cars, but as long as you are careful about not hitting curbs, and keep to asphalt, which the overwhelming majority of drivers do for an overwhelming fraction of their driving time, you are not likely to break axles.

A little common sense goes a long way. For instance, no matter which of your wheels are powered, there are simply some conditions when you're better off staying out of your car, like when freezing rain turns the roads into so many skating rinks.

Of course, stay off soft berms and clay ground, especially after periods of rain, or you may find yourself in the position of Richard III, as portrayed to devastating effect by Ian McKellen in the 1995 movie, set in a dystopian 1930s-like era. The final scenes show the king in battle, driving a Rover that gets stuck in the trampled English mud. Uselessly spinning his wheels, Richard exclaims, "A horse, a horse! My kingdom for a horse!"



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