Toward the end of the seventies, it seemed the 911’s days were numbered. Due to legal embroilments and a largely unjustified reputation, the rear-engined marvel was becoming feared by many, and the company was turning their attentions to a front-engined successor with a sweeter disposition.
The technologically advanced 928 arrived in 1977 with a more conventional layout and an air of added manageability. Thanks to the new Weissach axle, which mitigated the lift-off oversteer antics that marred the 911’s reputation, the 928 wasn’t made faster in most corners—but it was much easier to drive.
The Trouble With Lift-Off Oversteer
The lift-off oversteer characteristic caused by toe-out tendencies in the rear suspension, dramatic weight transfer, and engine braking was only worsened by advances in tire technology at the time. More grip encouraged drivers to increase corner entry speeds, and when overshooting the mark slightly, a natural lift of the throttle pitched the 911 into an abrupt slide. Though this characteristic is controllable, relished even, by the experienced driver, expecting a quick countersteering reaction from a member of the general public just wasn’t realistic.
The Weissach axle helped garner a friendly reputation for the 928.
The Weissach axle, known in German as the Winkel einstellende, selbst stabilisierende Ausgleichs-Charakteristik (angle-adjusting, self-stabilizing equalization characteristic), addressed this handling quirk by first inspecting the elasto-kinematic elements, better known as the rubber bushings between the axle components and the suspension. If they compress more on the front suspension points than the rear, and if this effect is supported by suitably adapted axle kinematics after lifting from the throttle, then the nervous toe-out condition is replaced by a stabilizing toe-in condition.
Putting this knowledge into practice required some unconventional testing procedures, including the installation of a passive steering system in the rear of an Opel Admiral. With one engineer sitting in the rear seats and steering their own wheel, they could study the effect of subtle rear steering inputs and build their Weissach axle upon this foundation.
The 928 and its Weissach axle laid the groundwork for the current rear-steering systems.
Fortunately, thanks to some brave and forward-thinking individuals, the 911 lineup was retained and made easier to handle with the Weissach axle; the 993 being the first generation to enjoy the fully developed version. Thanks to this technology, which laid the groundwork for the rear-wheel steering systems used in Porsche’s current lineup, we get to enjoy reduced steering effort, greater precision, increased stability, and greater usability for those not completely comfortable with rapid countersteering.