Short Take Road Test
It's nice to see GM be first for a change," remarked a public-relations rep at the recent full-line preview of General Motors' lineup of vehicles for 2002.
He was referring to one of the best ideas to come out of GM in years: rear-wheel steering for trucks.
You might remember rear-wheel steering as a promised fig leaf for goof-proof sporty-car handling that appeared in the late '80s. The theory was that by steering the rear wheels in the opposite direction as the fronts at low speeds, slow-speed maneuvering would be easier and the car would turn more sharply. Conversely, by steering the rear wheels in the same direction as the fronts at high speeds, the system would increase stability. Honda Preludes, Mazda 626s, Dodge Stealth R/Ts, Mitsubishi 3000GT VR4s, and Nissan 300ZXs were all available with rear steer.
Some of these rear-steer cars were so adept at getting into tight parking spots that you'd swear they were hinged in the middle. High-speed stability depended on the car, but at best, the four-wheel-steer cars were about as stable as a good two-wheel-steer car. At worst, the four invoked a spooky twitch at high speeds that was anything but comforting.
Since the cars that had these systems were far from huge and any extra high-speed stability was far from guaranteed, demand for four-wheel steering went the way of the in-dash record player; the last system was sold on the 1999 3000GT.
Then a light bulb went off somewhere in the cranium of the lumbering giant that is GM. The idea was so simple and right on that it's amazing it hadn't surfaced sooner: Use four-wheel steering on the vehicles that need it most--cumbersome full-size pickups. For now the system--it's known as Quadrasteer--is standard on only one GM pickup, the luxo $44,105 GMC Sierra Denali. Last year, this now highly zooty truck was called the C3.
Quadrasteer was co-developed by GM and Delphi Automotive Systems, and it cuts the Denali's turning-circle diameter from 47.3 feet to 37.4, a foot larger than a Honda Accord's. Using electric steering gear and computer control, Quadrasteer swings the rear tires in a variety of ways. There are three modes--two-wheel steer, four-wheel steer, and four-wheel-steer tow--which are selected via a dash-mounted button. The four-wheel-steer mode works like this: At less than 7 mph, the rears turn a maximum of 12 degrees in the opposite direction as the fronts. Between 7 and 40 mph, the computer gradually reduces the amount of opposite rear steer. At more than 40 mph, the computer then directs the rear wheels to turn a maximum of five degrees in the same direction as the fronts.
If you're not convinced of four-wheel steering's merits, you can always switch it off and go with two-wheel steering. In four-wheel-steer tow mode, the rear wheels behave nearly the same as they do in four-wheel-steer mode, but the speeds and angles are jiggered to provide increased stability when pulling something behind you and--we're not making this up--to prevent the possibility of driving into your own trailer.
Although we were amazed at the unexpected ease with which the 19-foot-long Sierra Denali snakes around a parking lot, its towing prowess impressed us most.
While towing a 7000-pound camper trailer at 60 mph in two-wheel-steer mode, we were instructed by Lorraine Babiar, the Sierra assistant brand manager, to do something that was farthest from our minds at the moment: Make a lane-change maneuver. We obliged, and as expected, jerking the steering wheel hard to the left and then to the right sent the trailer wagging so violently that we were sure the next stop on the itinerary was the nearby ditch. Somehow we stayed on the road. Next we performed the same test with Quadrasteer in the four-wheel-steer tow mode, and the trailer obediently followed the truck without any dangerous oscillations. With the trailer unhitched, we didn't detect any twitchy behavior, either. Very neat.
Quadrasteer adds a shocking 350 pounds to the pickup--even after replacing the steel fenders with plastic ones--but, says GMC, there is no reduction in towing capacity or payload. To provide clearance for the articulating rear wheels, the Sierra Denali has a five-inch-wider rear track, which necessitated the fender bulges.
The Sierra Denali will have the rear-steer truck market all to itself until spring, when Quadrasteer will be about a $3500 option on all GMC and Chevy full-size, extended-cab pickups. Unless Ford and Dodge develop their own four-wheel-steering systems, GM will have the most agile pickups for at least a year--the deal with Delphi gives the General exclusive use of Quadrasteer until August 2003.
