PORSCHE STABILITY MANAGEMENT The new 911 Carrera 4 is the first-ever Porsche to feature Porsche Stability Management (PSM), a combination of four-wheel drive designed consistently for sports motoring and electronic suspension control carefully geared to the character of the car. The result is not only a high standard of driving safety, but also that very special driving pleasure Porsche drivers have learnt to appreciate so much over the last 50 years. This objective calls for control and suspension management features different from those to be found in other cars incorporating similar systems. For PSM is conceived and designed for a routined, committed style of motoring. A Porsche will retain its agile, sporting and dynamic driving behaviour all the way to the most extreme limit. And thanks to the high standard of safety reserves offered by the suspension, the driver only has to intervene in the car's behaviour on dry roads when driving under near-racing conditions. At the same time PSM discreetly and almost unnoticeably corrects any minor deviations in directional stability attributable to load change or application of the brakes in a bend. Stopping Distances Even Shorter Than Before Porsche's engineers allow PSM to intervene more energetically at an even earlier point on wet or slippery roads and, in particular, on road surfaces with varying frictional coefficients. And it is here, too, that PSM makes stopping distances much shorter while keeping the car stable and firmly on course when applying the brakes. In its operation PSM follows two fundamental control strategies: First, it offers the well-known concept of longitudinal control with ABS anti-lock brakes, anti-spin control and the Automatic Brake Differential keeping the car smoothly on course when accelerating and applying the brakes on a straight or in bends. Second, PSM also offers lateral or transverse control keeping the car reliably on course even when subject to substantial lateral forces in a bend. The corrections required for this purpose are provided by the specific, carefully controlled application of the brakes. Any tendency to oversteer with the rear end of the car swerving round is counteracted by the exact, perfectly metered application of the brake on the outer front wheel in a bend. Understeering, in turn, is prevented by applying the brake on the rear inner wheel. Lengthwise dynamic control also comes in here to provide a supportive effect, E-Gas technology in the Carrera 4 serving to adjust the position of the throttle butterfly according to specific requirements. On the road, this means much easier and smoother steering. To ensure precise function at all times, PSM features a whole number of monitoring units. The wheel speed sensors introduced for the first time together with ABS not only provide information on the speed of the car, acceleration and deceleration, but are also able, by considering the difference in speed from left to right, to "detect" bends and their radius. Further units are the steering angle sensor, a lateral acceleration sensor and a yaw sensor serving to detect any drift inclination of the car. PSM: Faster Than Even a Routined Driver All data determined by the sensors are stored within the PSM computer, evaluated within fractions of a second and passed on as instructions to the E-Gas or brake system. As a result, PSM responds a lot faster in threatening situations than even the most routined driver. Really enthusiastic drivers wishing to try out the "natural" dynamic behaviour of their Carrera 4 on the race track are able to temporarily deactivate the lateral dynamic control provided by Porsche Stability Management simply by flipping a switch on the instrument panel. And even then the risk involved when taking the car into a power slide is reasonably limited, since all the driver has to do when the angle of the car becomes excessive is to step on the brakes in order to reactivate the dynamic control function. So under circumstances like this PSM is able to slightly "bend", but of course never fully override, the laws of physics.