Ackermanngeometrie

Ackermanngeometrie, known in English as Ackermann steering geometry, is a principle in automotive engineering that describes the relationship between the steering angles of the front wheels to enable them to trace concentric circles around a common instantaneous center. This arrangement minimizes tire scrubbing and improves handling during cornering.

In the ideal condition, the inner wheel angle δ_in and the outer wheel angle δ_out satisfy tan(δ_in) = L/(R − W/2) and tan(δ_out) = L/(R + W/2), where L is the wheelbase, W the track width, and R the distance from the vehicle centerline to the instantaneous center of rotation (ICC), which lies on the extension of the rear axle. The lines defined by the wheel steering axes intersect at a single point, the ICC, ensuring each wheel follows an appropriate circular arc.

In practice, many suspensions and linkages introduce deviations from exact Ackermann geometry. Modern vehicles often implement near-Ackermann steering by design or with electronic control systems in some cases. An "Ackermann error" describes deviations from the ideal condition, which can cause tire wear, increased scrubbing, and altered steering effort during turns.

The concept originated in the 19th century and remains a foundational criterion in steering design. While modern multi-link suspensions and electronic steering can approximate or adapt the ideal geometry, the basic idea of converging wheel axes to a common turning center continues to guide the arrangement of steering linkages in a wide range of vehicles.