Tag Archives: torque steer

Featurette – All-Wheel-Drive

(The Featurette section is a new series of articles about the little things in today’s automotive world that most of us probably don’t think too much about, but are either important enough or cool enough that we should know more about them. So, enjoy!)

All-wheel-drive is one of those automotive technologies that, like navigation systems or stability control, quietly sneaks into the mainstream while nobody’s watching. Like those systems, it’s something you probably did without on your first car (be it your shitbox or your parents’), but the next time you saunter into your local showroom to pick something out, you might just find it lurking under the chassis like Robert DeNiro. (Or, even worse, Sideshow Bob.)

Of  course, the salesman will probably throw a little extra spit in his hair and swing by to brag about how much “safer” all-wheel-drive is. But you don’t trust him! Here’s a man who still wears a beige tartan suit jacket he bought at Sears all the way back when Roebuck and Inc. were still with the place. His house has fake-wood laminate wallpaper. You do not want to trust anything he says.

So then, what exactly is the deal with all-wheel-drive?

Well, let’s start with the basics – what is it?

All-wheel-drive, or “AWD,” basically means power goes from the engine to all four wheels. Historically, most cars have been either rear-wheel-drive (RWD) or front-wheel-drive (FWD), each of which provides its own advantages. RWD usually makes for a better balanced car, as it shifts more drivetrain weight to the back axle, away from the  heavy engine. It also usually results in better performance, as each set of wheels can concentrate on one task – the front wheels on steering, the rear wheels on pushing.

FWD, however, improves traction by placing the drive wheels under the heavy engine, increasing the percentage of the vehicle’s body weight over them. It also increases interior space by eliminating the driveshaft between the engine and rear axle. However, making the front wheels handle both steering and propulsion can prove too much to handle, especially in powerful cars; this can result in torque steer, where the car weaves uncontrollably under hard acceleration. Plus, lightening the rear can cause the back end to swing out on slippery roads.

AWD, in theory, offers the best of both worlds. By putting power to all the wheels, it maximizes traction, making the vehicle safer and improving performance.

(On a side note, don’t confuse AWD and four-wheel-drive [4WD] – it’s a common rookie mistake, but easily remedied. 4WD is defined by one of two features – a low range, and/or an off-switch. A low range is a second set of gears designed to improve low-speed performance, and is designed for off-roading. An off-switch – well, it’s pretty self-explanatory, but basically allows the driver to put the vehicle into two-wheel-drive mode on dry roads. 4WD tends to be found in trucks and SUVs designed for off-roading; AWD is usually found on cars and car-based SUVs.)

Sounds good so far, right? Well, don’t go checking that AWD box on the order form just yet. (Unless you’re just screwing around on the build-your-own section of a carmaker’s website- which is how we spend about 80 percent of our unsupervised time here at CCO.)

First off, adding AWD almost always adds mass. Manufacturers have been working on reducing the  weight of their AWD systems, but for the most part, you’re still looking at a gain of around 100 pounds or more. As a result, fuel economy usually dives a tad. A BMW 328i with rear-wheel-drive gets 28 highway mpg, while its AWD counterpart gets 25; after 15,000 miles of highway driving, the RWD car will have used 64 fewer gallons of premium gas – or $176 worth at $2.75/gallon.

The added weight can also have a negative effect on performance. Note the italics, though. Whether or not AWD slows your car down or speeds your car up comes down to how fast your car would be without it. For cars with engines capable of pushing the U.S.S. Enterprise into warp speed, AWD’s increase in traction reduces wheelspin, enabling the car to put down more power more quickly (and overriding the detrimental effects of weight gain). However, wimpier cars (that is, most of them) don’t have those sorts of problems with traction under acceleration, so the AWD system only serves as a burden on the drag strip.

(AWD also provides improved handling, but again, that’s in large part a matter of how quickly you’re taking those turns, and most cars don’t take them fast enought to make a significant difference.)

There’s a second downside to AWD systems: they  usually add cost, too. Different manufacturers tack on different amounts, but you should plan on paying at least $1000 more for the feature.

So should you spring for all-wheel-drive next time you buy a new car? Well, if you take away one point from this feature(tte), make it this. On most cars, all-wheel-drive is a safety feature, not a performance feature. Its primary focus is to give you added traction in slippery situations. If you live somewhere like Vermont or Minnesota, where snow can sit on the ground for six months, it’s probably worth the extra money. If you live in the Sunbelt and are worried about the five days a year you venture north, save the cash for your A/C bill and just drive slowly if things get slick. And if you’re somewhere inbetween? If AWD makes you feel more secure and you don’t mind the cost, go for it – but a good set of all-season tires and an attentive driver will be just as safe 95 percent of the time.



Filed under Featurettes