Chassis, Steering, Brakes

Open top dynamics for the open road

• Sporty handling inherited from sedan challenges class benchmark
• Greatly improved ride refinement and NVH levels
• Saab ‘ReAxs’ - unique rear wheel steer characteristic
• Excellent steering response and feel
• Braking system includes MBA, CBC and EBD as standard
• Progressive, Saab-tuned ESP®

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

The Convertible’s impressive chassis composure, handling agility and ride refinement place it among the very best on the market.
Like the sedan, the Convertible is the product of a rigorous development program, designed to combine the benefits of front wheel drive - predictability and excellent driver feedback - with new levels of chassis control for a more rewarding driving experience.

A rigid body structure and optimized suspension are the foundations on which the Convertible's chassis poise, refinement and impressively low levels of noise, vibration and harshness have been developed..

These innate abilities are backed up by Mechanical Brake Assist (MBA) and 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 standard for Aero and optional .on other variants..

Superior Handling
Today’s premium convertible customers are prepared to make few, if any, concessions to the absence of a fixed roof. Inherent losses in body rigidity must, therefore, be largely recovered by careful design, particularly around suspension mounting points, to prevent the chassis’s handling and ride composure being compromised.

The work of the chassis engineers was made easier by the Convertible’s separate, but parallel, development program alongside the Sport Sedan.. They benefited from the strategic decisions made by structural engineers to ensure that the architecture and ‘hard points’ for the 9-3 product range could be properly adapted to meet the needs of an open-top car. (A full description of this work can be found in the Body Structure section).

Compared to the 9-3 Sport Sedan, the weight distribution of the Convertible is slightly more favourable, in part due to the addition of the soft-top and its operating mechanism. The front/rear ratio of 55/45 compares well against the 60/40 split of the sedan and helps to offset a 10 per cent increase in kerb weight.

To deliver the high standard of ride quality expected in this class of car, engineers have also sought to minimize unsprung weight. As a result, 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 aluminium.

Suspension Design
In order to maintain a consistent suspension geometry - as well as helping to raise the chassis’s torsional rigidity – bracing rods are bolted to the rear sub-frame. These ‘V-rods’ run diagonally forward, from near the inboard mounting point for each lower suspension link, into the attachment point for the trailing toe link, reinforcing the sub-frame's fixing to the body.

And to further eliminate the possibility of any slight movement, four metal sleeves, instead of polymer bushes, are used at both the front and rear sub-frame mounting points.

With these measures in place, the chassis team concentrated on tuning the Convertible’s spring and damper rates, in order to maintain the sporty handling characteristics of the sedan.

The front MacPherson struts keep their de-coupled top mountings, separating the damper and spring loadings, and the aluminium lower control arms are attached, as before, to a hydroformed (hollow section) front sub-frame, including hydraulic bushes on the rearmost mounting each side for optimum damping. There is a single, 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. The trailing toe-link and lower transverse link are in aluminium and, like the front suspension, bushings are stiff for lateral forces and relatively soft longitudinally.

Apart from offering a more compliant ride, the multi-link suspension arrangement also allows greater scope for optimizing both handling and ride characteristics, in addition to reducing the amount of road noise transmitted to the interior. For tautness, the Convertible dispenses with the shear bushings in the top rear damper mountings, as fitted to the Sport Sedan.

Saab ‘ReAxs’ – passive rear wheel steer
Out on the open road, the Convertible's sporty handling characteristics are rewarding and ‘involving’ for the driver due to a unique, passive rear wheel steer characteristic, known as Saab ReAxs, first seen on the Sport Sedan.

The toe-links in the rear suspension and the use of ball joints, instead of rubber inboard and outboard suspension bushings, allow 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, ie. toe-out for the outer wheel and toe-in for the inner wheel.

Depending on vehicle speed and the radius of a bend, which will vary the consequent loadings at the rear axle, one degree of steering movement at the front wheels would typically produce a small but significant deflection of about one hundredth of a degree at the rear. 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 its 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.

Precise Steering
The power steering on Saab cars is widely acknowledged for achieving just the right balance between assistance and ‘feel’. In the straight ahead position there is virtually no assistance, in order the give the driver as much direct control as possible, and even at low speeds, when there is more assistance, the driver’s feel for the road surface is never impaired

The rack and pinion steering system for the 9-3 Convertible continues this tradition. The hydraulic pump is camshaft-driven with gasoline engines and the rack is mounted low down at the back of the front sub-frame. With diesel engines, an electro-hydraulic system is fitted, which uses a pump driven by a computer-controlled electric motor as a further contribution to improved fuel consumption.

The geometry and tuning of the front and rear suspensions also combine to give the steering its distinctive feel, linearity and responsiveness. At 2.97 turns from lock to lock, it is the quickest steering yet fitted to a Saab car.

Braking System
The performance of the powerful steel disc brakes is among best in class, giving a consistent pedal feel and showing particularly good resistance to fade under repeated heavy applications.

In EU specification, three brake sizes are fitted according to engine power. For all four cylinder engines, except the 210hp and 200 hp BioPower versions, 285 mm front (ventilated) and 278 mm solid rear discs are fitted. For the 210 hp and 200 hp BioPower engines, they are 302/292 mm (both ventilated) and for the Aero 2.8V6 turbo and TTiD engines these are increased to 314/292 mm.

High speed braking stability is particularly impressive, largely due to the Saab ReAxs control of the rear suspension geometry. This effectively ‘preloads’ the rear tyres by applying some lateral force through toe-in as braking commences.

An automatic brake boost feature, Mechanical Brake Assist (MBA) increases braking pressure from the master cylinder when the driver stamps hard on the brake pedal. This stops the vehicle quicker and also activates the car’s ABS more effectively.

A four channel ABS (Anti-lock Braking System) and a Traction Control System (TCS), with additional electronic throttle control, are both standard fitment. The other standard electronic brake control functions utilise the ABS wheel speed sensors and the variable valving at each wheel.

New for Saab in the 9-3 range is the introduction of Corning Brake Control (CBC), which is activated when the car is cornering under heavy braking. Brake pressure is individually varied between all four wheels so as to keep the car stable, minimising any snap oversteer or understeer characteristics.

Electronic Brake force Distribution (EBD) ensures an optimum braking force is always applied at both axles for maximum stability under heavy braking.

All four brake discs have full size dust shields. These ensure braking performance is not impaired by large amounts of snow, mud or dust jamming the calipers.

Advanced Electronic Stability Program (ESP®)
The fine chassis dynamics of the 9-3 Convertible can be supplemented by the option of an advanced, Saab-tuned ESP® system, which is designed to gently counteract over-exuberance or misjudgements from the driver.

It has been honed by technicians using dedicated software to match the behavior of the 9-3 Convertible’s chassis. The ‘intelligent’ system is extremely progressive in use and is designed to function almost imperceptibly, avoiding harsh interventions when the chassis has already reached the limits of adhesion.ESP® is fitted as standard with the Aero 2.8V6 turbo engine and is specially tuned for sporty driving, intervening progressively when the limits of adhesion are being reached.

A yaw sensor in the center of the car detects movement around the vertical axis and a sensor on the steering column measures the steering angle being applied. Inputs from these sources are then correlated with the speed of the car.

The system is extremely flexible and it is programmed to execute whatever actions will most effectively prevent the onset of a loss of control. Depending upon the chassis’s disposition, it is possible for braking to be applied via the ABS system to just one or all four wheels at once, in addition to control of the electronic throttle.

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