Steering geometry is one of the many tools at a race car designer’s disposal to ensure the car extracts maximum performance from all four tyres. In this Tech Explained article, we will cover the origins and purpose of what is known as Ackermann Steering geometry and how its variations can affect tyre performance across a vehicle’s operating range.
Defining Ackermann Steering
Consider a low-speed cornering manoeuvre, where all tyres are in pure rolling condition, and there is no vehicle sliding present. As the vehicle travels along a curved path, all four tyres follow unique trajectories around a shared turn centre, as defined by the blue arcs in Figure 1. 
Figure 1: Simplified depiction of Ackermann Steering configuration The different curvature radii mean that to avoid sliding, the steering geometry must steer the inside front tyre at a larger angle than the outside front. Ackermann Steering refers to the geometric configuration that allows both front wheels to be steered at the appropriate angle to avoid tyre sliding.
For a given turn radius R, wheelbase L, and track width T, engineers calculate the required front steering angles (?_(f,in) and ?_(f,out)) with the following expressions:
The difference in front-wheel steer angle as a function of the input steer angle is known as Dynamic Toe. If the vehicle dimensions are known, it is possible to construct a curve of the desired toe change for the full range of expected turn radii, such as the examp...