A SHARPER CHASSIS FOR A SPORTIER SAAB
NORCROSS, Ga. - The new Saab 9-5 range's updated appearance is only part of the improvements for 2002. In addition, the new 9-5 has become sharper. Sharper in the way it steers; more positive in the way it handles. The result is an exhilarating and communicative drive with a stronger emphasis on Saab's sporting character.
Key changes have been made at the front of the car to make it more responsive and quicker to react to driver inputs. The overall front-to-rear balance has also been honed to give the new Saab 9-5 range flatter, more consistent handling, while also reducing cornering pitch.
"We looked at what we had achieved with the Aero - which seems to have been universally liked - and then applied that car's sportiness to the rest of the new Saab 9-5 range," commented Sonny Bergman, head of vehicle dynamics. "But we also took the opportunity to upgrade the handling and performance characteristics of the Aero model at the same time. After all, there's always room for improvement."
Bergman and his team concentrated on improving the car's front-end responsiveness and flattening out the pitch-induced roll during hard cornering. The front springs have been stiffened by 10 percent, while the diameter of the front anti-roll bar has been increased by 1mm on all models.
The shock absorber settings have also been changed to accommodate the increased stiffness of the front springs and provide firmer control of the car's balance and poise during cornering. There are minor variations in spring and shock absorber rates for each 9-5 model to allow for the differing weights of the various powerplants, but the behavior has been designed to remain consistent from model to model.
The upper strut mountings have also been strengthened to improve longitudinal rigidity and better lateral load response. This results in a sportier driving characteristic and a slightly firmer ride, more in keeping with the new 9-5's sport-touring personality.
Stiffer front subframe lightens the load
The front subframe, used to isolate road shocks more effectively from the driving compartment, has received a significant upgrade. Like the springs, the subframe has been stiffened, but it has also been lightened. Both the subframe and the steering knuckle are now made of aluminum for lightness and strength.
The steering rack, located at the rear of the front subframe, has been changed to match the more effective handling characteristics resulting from the spring and shock absorber changes. New, longer steering arms are coupled to the existing steering rack. While initially lowering the gearing, it works more effectively with the sharpened front-end chassis modifications, offering a greater degree of driver confidence, comfort and control, while still providing excellent feedback.
Stiffening the front torsion bar and re-tuning the steering valve gear has further enhanced steering response. Although this means less steering assistance in the straight-ahead position, it greatly improves steering feel. This means the driver can better "read" the changing road surfaces for optimal driver/chassis information interaction.
Retuned rear suspension, too
The same spring and shock absorber changes incorporated into the front suspension have also been applied to the rear suspension set-up. The multi-link suspension at the rear is also mounted on a separate subframe, attached to the rear body structure by four large-volume elastomer bushings. To increase the responsiveness at the rear, the bushing in the system's trailing-arm set-up has been stiffened. Again, the benefit is a more responsive and sharper-handling chassis.
"It has made a big difference," Bergman said. "These spring changes make the back end respond more quickly and more consistently. You'll notice less movement in the back, especially in the 9-5 Arc model with the V-6. The ride's firmer but the pitch has gone."
Brakes on the Arc and Aero models have been upgraded also. The size of the rear discs has been increased, and include ventilation for improved cooling during hard braking.
The final changes concern the four corners - the wheels. There's a new generation of Michelin tires that have been specifically tuned to the requirements of the new Saab range. These are available in 16-inch or 17-inch sizes along with an all-weather tire. The new tires provide better stability and dead-center feel, while also contributing to the chassis's improved turn-in and reduced understeer.
Twelve go testing - from Arizona to the Arctic Circle
Bergman has overseen the 18-month development process with 11 other engineers. Three have been working on the steering feel, two on the engine mounting points, and six on the basic chassis parameters - such as tire compatibility and shock-absorber rates.
Initial testing was carried out at one of GM's US test tracks at Mesa in Phoenix, Arizona, followed by time in the ice and snow of the Scandinavian Arctic Circle. Since last autumn, the team has been honing the final touches to the car in Spain.
Benchmark cars to assess the Saab's progress included the Audi A6, BMW 5-series, Mercedes-Benz E-class and Volvo's S80 model. Each was assigned a parameter the Saab had to beat. For example, the new 9-5 range had to beat the 5-series on steering feel; the Volvo on comfort; and so on.
"I think you'll be impressed with what we've achieved," Bergman said. "The steering, in particular, is excellent, which is matched by much better handling and a sportier ride. The car now feels like a smaller car to drive - more agile. We've given it a very sporty flavor."