Auto Tech: GM Quadrasteer

The Automobile Journalists Association of Canada (AJAC) presents an annual award for the year’s “Best New Technology”. This year, eight technologies were presented to the AJAC technology panel for their consideration. General Motors chose their new Quadrasteer system to show off an interesting and practical new technology.

Quadrasteer is GM’s name for their four wheel steering. The system is first available on the 2002 Sierra Denali pickup and will be available on other GM extended cab pickup models in 2002. Four wheel steering is not new. Honda produced cars with mechanically operated four wheel steer in the early 90’s. The difference with GM’s system is that it is a continuously variable electronic system and it comes on full size vehicles that benefit greatly from the advantages of four wheel steering.

Drivers can select from three Quadrasteer modes of operation by pressing a button on the dash. In “2WS” mode (two wheel steer), the rear wheels remain in a centre position and the truck drives like a regular extended cab pickup. This is also the default mode. If the system detects any problems, a centering spring in the rear steering rack moves the rear wheels back to the straight-ahead position. Press the button again and the “4WS” indicator lights up.

After driving the truck, I suspect most driving time will be in “four wheel steer” mode. At slow speeds, less than 65 kph, the rear wheels steer in the opposite direction of the front wheels. This enables the truck to turn with amazing agility. I drove the truck though a cone-lined course on the track and was astounded by how easy it was to squeeze through the tight spots. I would have said it was impossible to drive the truck in those tight corners, but seeing is believing, and the truck motors through with ease.

At speeds above 65 kph, the front and rear wheels steer in the same direction. This increases agility and stability at highway speeds during lane changes or sudden maneouvers. It gives the driver a feeling of comfort and security. I thought driving the vehicle in four wheel steer mode would feel unusual. Instead, the steering and handling feel very natural and there are no mental adjustments required to drive with Quadrasteer. The only drawback I could see would be when returning to a vehicle without Quadrasteer – it would be easy to think you could park in a spot when in reality conventional steering could make it almost impossible.

The third mode of operation is “4WS tow”. In tow mode, the system reduces the amount of rear wheel steer at low speeds and increases rear-wheel steer at higher speeds. This provides more stability for trailers than regular 4WS mode.

The Quadrasteer system uses several sensors and a microprocessor to steer the rear wheels. A steering wheel sensor detects the angle and speed of the driver’s inputs. A vehicle speed sensor input signals the computer when to steer the wheels in different directions. A rear wheel position sensor monitors position of the electrically-driven rear steering rack. All this information is wired into the microprocessor controller which is contained in a large rugged sealed case mounted under the truck box and in front of the spare tire.

The maximum steering angle of the rear wheels is limited to 12 degrees but the actual amount of steering angle varies with vehicle speed, steering input, and mode selection. In reverse, the rear steering has a maximum of 5 degrees angle. These numbers seem small, but they make a dramatic difference in the manoeuvrability of the truck. GM’s Quadrasteer is an impressive new technology.

This is the last in a series of eight articles showcasing new technology presented to AJAC’s technology panel. The votes have been entered, but even the AJAC panel members don’t know the outcome. The winner will be announced in the new year at the Canadian International Auto Show and we will keep you informed on www.Autos.ca. See if you agree with the panel’s choice.