I must confess that it took me almost a day and a half to appreciate the fact that GMC's gargantuan Sierra Denali pickup represents truly cutting-edge news for 2002. After all, it's really just a re-badged C3 whose debut in '01 introduced the world to GMC's giant 6.0-liter V-8 mated to an all-wheel-drive powertrain. But then I started pushing buttons; and when the indicator labeled "4WS" illuminated, nothing happened.
Not at first, that is. When I turned at the next intersection, I experienced one of those vague seat-of-the-pants sensations that something unusual was taking place. The rear end of the truck seemed to speed up on me, independently of the front. Now, that's odd.
And when I parked at the post office, I almost clipped the car I was parking aside, because this hulking beast of a truck made the turn so much more abruptly than logic or my experience led me to anticipate. Such, I have since learned, is the nature of the Quadrasteer system, which endows a land yacht like the Sierra Denali with the unprecedented maneuverability of four-wheel steering.
Sure enough, the clues were there all the time. Look under the cargo bed at the rear axle, and you can see the telescopic actuators that turn the rear wheels about the axes of their unorthodox steering knuckles. The body flares over the rear wheels are another giveaway: they're meant to enlarge the wheel well to accommodate the greater space necessary for housing the rear wheels at their maximum turning angle.
What's less obvious is the principle of Quadrasteer. When you're parking or traveling slowly, the rear wheels turn in a direction opposite that of the front wheels. This puts the truck on a truly circular trajectory and slices the turning radius by 20 percent. In two-wheel-steering mode, the Sierra describes a 46.2-ft diameter circle, but in 4WS that narrows to 37.4 ft —virtually the same figure achieved by Saturn's tiny sports coupe (at 37.1 ft).