|
GMC Sierra Denali truck maneuvers with four wheels steering
Bob Plunkett
Date Posted: 5/10/2005
|
TORREY PINES, Calif. -- This is it: The ultimate pickup, stoked with power from a massive engine, stuffed with luxurious comforts in a four-door and five-seat cabin, then outfitted with sophisticated electronic controls that make the big rig as easy to maneuver around a crowded parking lot as a small sports car.
Call it Denali, top trim for the Sierra 1500 full-size truck by GMC of General Motors.
A humongous 6.0-liter V8 engine sits beneath that scored hood and it carries the strength of 325 horses, plus as much as 370 lb-ft of torque at 4000 rpm.
That's the maximum power rating for a full-size pickup in the half-ton and light-duty class.
It's strong enough to push the truck's gross combined weight rating (GCWR) to 16000 pounds and peg the trailer tow limit at 10000 pounds.
Denali also employs a heavy-duty automatic transmission to handle all of the torque produced by that big V8, plus the Autotrac automatic active transfer case with all-wheel-drive system channeling power to every wheel for constant traction over wet as well as dry pavement.
But there's more: For 2002, Denali adds a sophisticated steering system that not only turns the front wheels but rear ones too.
What's the advantage of steering with all four wheels?
It enables the truck to maneuver at slow speed with amazingly tight turns that match the nimble movements of a small car, while at highway speed the system produces more straight-line stability and vehicle control regardless of the on-board load.
The new four-wheel steering mechanism -- Delphi Automotive's Quadrasteer -- electronically controls the direction of rear wheels so all four wheels work together more efficiently than when only the front ones turn.
At speeds below 40-to-45 mph, rear wheels swing slightly in opposite direction to the front wheels, as governed by the smart electronic controller. The slower the speed, the more movement comes from the rear wheels.
This action of changing the direction of rear wheels at a slow speed actually abbreviates the size of the turning circle for Denali -- the diameter of the turning circle decreases to less than 38 feet, which virtually matches the turning circle of Saturn's SC2 subcompact sports coupe.
We tested the system on a campus parking lot at the University of California, San Diego, in Torrey Pines.
Orange traffic cones defined a narrow steering course of side-by-side straights linked by tight U-turns. Switch off Quadrasteer via a dashboard toggle and we plowed cones at every turn. Switch on the system for a run over the same course and at every corner the Quadrasteer magic enabled our Denali to hook a wrap-around left or right and stay well within borders without tipping a single cone.
Making a left-hand corner turn to park in a narrow slot was equally easy to accomplish with the system operating -- and impossible when it was not.
On a trek down the I-805 freeway, we discovered another advantage to Quadrasteer.
At speeds above 40-to-45 mph, the system turns the rear wheels slightly in the same direction as the front wheels. This action reduces yaw or rotational motion in the conflict between front and rear wheels that's typical for a speedy truck -- the tail wagging the dog, so to speak.
You notice the extra control most when changing lanes because Denali seems to zip quickly into the next lane with little wiggle from the rear end, but it remains quite stable when steered in a straight line with no detectable lateral motion at the tail.
Now tow a huge trailer with the Sierra Denali equipped with Quadrasteer.
Our tow-test rig, extending forever behind the truck, seemed like an intimidating load to lug around town -- but it didn't work that way when underway because the assistance provided from four-wheel-steering ended up adding a new pivot point at the front of the trailer when maneuvering in traffic or turning corners.
It was convincing to take a hard right at an intersection with all of that load stretching behind and watch it follow obediently in an easy arching turn -- no sweat.
For trailer towing or just moving the truck around town in tight confines, Quadrasteer becomes an easy-to-demonstrate advantage to the driver. And the high-tech system is standard equipment but exclusive to Sierra Denali.
Modifications to the truck's chassis, track and suspension were made to assist the Quadrasteer equipment.
A higher capacity rear axle was added with greater GVW rating and boosted payload capacity -- to 1722 pounds.
The rear track width was increased by five inches to enhance straight-line stability, but a wider track necessitated new flared fenders to cover bulging wheels.
Also, applying the ZX3 ride control system brings driver-selectable shock damping through electronic control of monotube shocks. Punch a switch on the dash to pick preferred ride quality -- Smooth Ride or Control/Trailering.
This Sierra also wears stronger high-capacity disc brakes with large rear calipers lifted from the three-quarter-ton Sierra 2500 truck as counterbalance for the truck's strong acceleration and cornering ability. In addition, the system includes four-wheel ABS for straight brake tracking, plus a dynamic rear proportioning device to modulate brake pressure evenly.
The heavy-duty automatic transmission with four forward gears increases the maximum torque capacity to correspond with output of the engine, and a powertrain control module manages shift timing, the shift firmness and torque-converter clutch operation. A button on the shift lever may be used to increase the time between gear shifts and quicken the shift sequence to assist when pulling a trailer.
Besides the slant to strong muscle and heavy-duty hardware, Sierra Denali supports a four-door passenger compartment stuffed with luxurious comforts and sophisticated electronic devices that include high-tech communications equipment. The standard package brings a driver information center mounted on the dashboard, an advanced stereo system with six-disc CD changer and the hands-free OnStar telecommunications link with 24-hour availability for in-vehicle safety, security and information services.
Behind the 77.8-inch cargo box, a receiver hitch is integrated below the tailgate. The box is covered by a vinyl tonneau lid shaded to match the truck's paint.
Base MSRP for Sierra Denali tallies to $43,385 plus a $720 delivery fee. Options are limited to color-keyed running boards and an engine block heater.
|
| Vehicle Specifications: |
| 2002 GMC SIERRA DENALI AWS Specs |
| Description: |
Full-size pickup truck |
| Model Options: |
Full-size pickup truck |
| Wheelbase: |
143.5 inches |
| Overall Length: |
227.7 inches |
| Engine Size: |
OHV 6.0-L V8 |
| Transmission: |
Auto/4 |
| Drive: |
AWD Autotrac |
| Braking: |
Power 4-disc/ABS |
| Airbags: |
2 (front) |
| Gross Weight: |
7200 pounds, Maximum GCWR:16000 pounds |
| Towing Capacity: |
Maximum trailering capacity..10000 pounds |
| Gas Mileage: |
11/14 mpg |
| Price: |
$ 43,385 |
|
|
