## 2 Materials and Methods  
For the sake of carrying out experimental driving stability measurements on a passenger car, an alternative to the commercially available SkidCar was mounted on an individually built vehicle (the experimental car 4 WS), in the Laboratory of the Faculty of Transport Engineering at the University of Pardubice.  
With the help of ASC, it was possible to optionally change the radial reactions of the vehicle wheels and thus their adhesion [31]. The auxiliary wheels of the alternative SkidCar system were free to rotate around the vertical axis, so they did not lead the vehicle, but only transmitted vertical forces. The reduction of the adhesive force on the vehicle wheels was achieved through the reduction of the radial reaction of these wheels. The car was lightened by a hydraulic circuit controlling the vertical position of the ASC frame above the ground, thereby reducing the radial reactions of the vehicle wheels. For this reason, the vehicle could be brought to the limit of stability, i.e., to skid at a lower (safe) speed, even on dry asphalt. More detailed specifications and the use of ASC is processed in [14].  
The ASC frame was attached to the body of the experimental vehicle through a screw connection. The front crossbar with the front wheel units was located behind the front axle axis, whereas the rear crossbar with wheel units was in front of the rear axle axis. The change in the wheels' radial reaction was set prior to the experimental measurement. The adjustment was performed by a hydraulic extension of the wheel unit. Detailed information on ASC is given in [13].  
The current state of the ASC (Figure 1) consists of a steel demountable frame with material support, highlighted in Table 1. The frame comprises of two crossbars, two side members and four wheel units. The wheel units embody free-rotating rubber wheels, bearings, steel tubes and mechanical transmissions allowing the rubber wheels to be extended and retracted. Side members and wheel units are not subjected to optimization in this work. The frame is attached by a screw connection to the truss frame of the experimental vehicle. The side members are mounted on both sides of the car between the crossbars and increase the longitudinal stiffness of the ASC.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & \multicolumn{2}{c}{\(\mathbf{Z_{SCRL}}\) (N)} & \multicolumn{2}{c}{**Deviation (\%)**} & \multicolumn{2}{c}{\(\mathbf{Z_{SCRL}}\) (N)} & \multicolumn{2}{c}{**Deviation (\%)**} \\ \hline
**k (-)** & **Experiment** & **Simulation** & & **Experiment** & **Simulation** & \\ \hline
1.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 \\
0.8 & 848.0 & 834.0 & 1.7 & 839.0 & 831.0 & 0.9 \\
0.6 & 1696.0 & 1677.0 & 1.1 & 1677.0 & 1658.0 & 1.1 \\
0.4 & 2544.0 & 2516.0 & 1.1 & 2516.0 & 2498.0 & 0.7 \\
0.2 & 3393.0 & 3439.0 & 1.4 & 3354.0 & 3422.0 & 2.0 \\
0.0 & 4241.0 & 4227.0 & 0.3 & 4193.0 & 4143.0 & 1.2 \\  & \multicolumn{2}{c}{\(\mathbf{Z_{SCRL}}\) (N)} & \multicolumn{2}{c}{**Deviation (\%)**} & \multicolumn{2}{c}{\(\mathbf{Z_{SCRR}}\) (N)} & \multicolumn{2}{c}{**Deviation (\%)**} \\ \hline
**k (-)** & **Experiment** & **Simulation** & & **Experiment** & **Simulation** & \\ \hline
1.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 \\
0.8 & 455.0 & 456.0 & 0.2 & 450.0 & 453.0 & 0.7 \\
0.6 & 910.0 & 956.0 & 5.0 & 900.0 & 937.0 & 4.1 \\
0.4 & 1365.0 & 1430.0 & 4.7 & 1350.0 & 1413.0 & 4.7 \\
0.2 & 1821.0 & 1872.0 & 2.8 & 1800.0 & 1855.0 & 3.1 \\
0.0 & 2276.0 & 2338.0 & 2.7 & 2250.0 & 2315.0 & 2.9 \\ \hline \end{tabular}  
* Average deviation: 2.2%; maximum deviation: 5.0% \(Z_{SCRL}\)—radial reaction of the support front left wheel (N); \(Z_{SCRL}\)—radial reaction of the support front right wheel (N); \(Z_{SCRL}\)—radial reaction of the support front right wheel (N); \(Z_{SCR}\)—radial reaction of the supporting rear right wheel (N); and \(k\)—raising the car (-).  
\end{table}
Table 1: Validation of the experimental measurement model.