# On the Influence of Suspension Geometry on Steering Feedback
## 1 Introduction
Where a passive LSD or these advanced devices are adopted on the front axle, the control of torque steer phenomena should be taken into account from the very early design stages. Electric power-assisted steering (EPAS) systems also offer the opportunity to cancel out torque steer by means of suitable control strategies [29]  
It is, however, where the torque can be controlled independently on each wheel that the torque vectoring concept can be taken to new heights [30]. On electric vehicles with a multiple-motor powertrain, for instance, the torque vectoring can be achieved with individual wheel torque control. Figure 1: Special McPherson front suspension with separate steering axis (courtesy of Honda Press). This feature can significantly enhance the cornering response, driving stability, performance and active safety whilst improving vehicle dynamic properties and/or the fun-to-drive attitude of the car. Torque vectoring can also increase energy efficiency through the appropriate design of the reference understeer characteristics and the calculation of the wheel torque distribution providing either the desired total wheel torque and a direct yaw moment [31; 32; 33]. Today, the evolution of the automotive world towards electrification means that a variety of hybrid and electric cars with different powertrain/transmission architectures can be found on the market. In the specific case of an electric or hybrid car, one or two independent electric motors can be installed on a driving axle. Therefore, it is possible to use the control system of these motors to deliver different torques to the left and right wheel. A front driving axle with independent motors therefore raises the bar of the torque steer challenge. Furthermore, in the case of an electric powertrain, the very fast response times related to a driver input could generate sudden torque peaks on the steering wheel, thus making feedback even worse than traditional FWD cars equipped with an LSD or an actively controlled differential. This paper is aimed at providing an insight on the torque steer phenomenon in light of the shift towards full electric vehicles even in the high-performance market segment, in order to understand which geometric parameters of the car it is directly connected to, starting with a comprehensive theoretical background. Examples of suspension kinematic re-design are proposed to minimise the torque steer effects with the help of a specific software. Such a tool has been self-developed within the Automotive Engineering Group of Brescia University by the authors of this work. The development process is reported in [34]. A thorough validation was carried out by comparing results with commercial tools, like Lotus Suspension Design (Shark(r)) by Lotus Engineering and with the Adams multi-body package. This proprietary tool:  
* enables the design and analysis of all kinds of suspension geometries (from swing arm to full multi-link to typical racecar layouts), including kinematics of the complete steering line;
* allows any kind of user to quickly perform a ground-up design;
* can plot all the relevant suspension characteristics;
* can overlay results coming from incremental design steps;
* features a specific setup mode to simulate the effects of suspension adjustability;
* features the direct export of suspension kinematics towards professional simulation packages like CarSim(r) and VI-CarRealTime(r);
* has been successfully employed in some previous works [35; 36]. Finally, a simulation campaign is carried out on VI-grade's VI-CarRealTime(r) (VI-CRT) simulation environment with standard sine steer and track laps. The results will be reported.