2004 9-3 Convertible Chassis

The fine chassis dynamics of the new Saab 9-3 Convertible deliver the kind on the road performance that is promised by its sporty looks and purposeful stance. Hardly surprising, since it shares the core chassis and suspension components with the widely-acclaimed 9-3 Sport Sedan.

Key to its enhanced abilities is a rigid body structure - at 11,500 Nm/degree of deflection, it is almost three times stiffer than that of its predecessor - and an all-new suspension layout. These are the solid foundations on which Saab test engineers have developed the chassis poise, refinement and impressively low levels of noise, vibration and harshness that distinguish a premium class, open top car.

When work began on the all-new Saab 9-3 series, Saab designers and engineers were for the first time able to ensure that the needs of a Convertible variant were given the same priority as those of a sedan. The result was the installation of 'second' supplementary chassis, an additional 'ring of steel' linking and reinforcing the front, rear and side structures. This helps to compensate for the loss of structural rigidity due to the absence of a roof and also benefits handling, ride refinement and, of course, crash impact resistance.

The proportions of the new Convertible were also a good starting point. Compared to its predecessor, it has a broader 'footprint', a 71 mm increase in wheelbase more than offset by the relatively larger 74 mm and 63 mm increases in front and rear track. The ride height is also 10 mm lower.

Suspension layout

In order to maintain a consistent suspension geometry - as well helping to raise the chassis's torsional rigidity - bracing rods are bolted to both front and rear sub-frames. And to further eliminate the possibility of any slight movement, hard metal sleeves replace the compliant polymer bushes fitted to the sedan at the sub-frame mounting points to the body, four at the front and four at the rear.

The front MacPherson struts keep their de-coupled top mountings, separating the gas damper and spring loadings, and the lower control arms are attached to a hydroformed (hollow section) front sub-frame. There is a direct-acting anti-roll bar and, for good directional stability and ride comfort, the suspension layout is designed to be largely impervious to lateral forces and compliant longitudinally.

The multi-link, independent rear suspension incorporates three transverse and one longitudinal link, gas dampers, coil springs and an anti-roll bar. Compared to the rigid, torsion beam used for the previous Convertible, the new layout has far more longitudinal compliance. Like the front suspension, bushings are stiff for lateral forces and relatively soft longitudinally.

For better ride quality, unsprung weight is minimized. All four wheel carriers (hubs) and brake calipers, the lower control arms in the front suspension and the toe and lower links in the rear suspension are made of aluminum.

Saab 'ReAxs' - passive rear wheel steer

Out on the open road, the new Convertible's sporty handling is rewarding and 'involving' for the driver due to a unique, passive rear wheel steer characteristic, known as Saab ReAxs , first seen on the 9-3 Sport Sedan.

Toe links in the rear suspension and the use of ball joints, instead of rubber inboard and outboard suspension bushings, allows a much closer control of wheel movement. As a result, under cornering loads, the elasto-kinematics at the rear axle induce a very slight deflection of both rear wheels in the opposite direction to the steering input, i.e. toe-out for the outer wheel and toe-in for the inner wheel.

This is sufficient to prevent excessive understeer, where the driver is forced to apply progressively more steering lock to turn the front end of the car, increasing the scrub angles of the front tyres. The Saab ReAxs characteristic overcomes this 'crabbing ' effect, helping the tail of the car follow the direction of the front wheels, instead of its nose. For the driver, this makes the car better balanced and more fun to drive, helping it turn in and respond more closely to steering inputs.

Braking System

Two systems are fitted as standard, according to engine power. For 175 bhp variants, 285 mm front (ventilated) and 278 mm rear discs are fitted. For the 210 bhp engine, these are increased to 302 mm at the front (312 mm on some markets) and 292 mm at the rear, both ventilated.

An automatic brake boost feature, Mechanical Brake Assist (MBA), is introduced for the first time on the new 9-3 range. The Convertible's innate abilities are also backed up with a full array of electronic driver aids, including ABS (Antilock Braking System), TCS (Traction Control System), Cornering Brake Control (CBC) and Electronic Brake force Distribution (EBD), all fitted as standard. A Saab-tuned ESP (Electronic Stability Program) is optional and standard for the Aero model.

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