## 3 Results  
### Longitudinal Center of Gravity and Lateral Stability  
Figure 5 shows the determined longitudinal (\(l_{f}\)) and lateral (\(\Delta y\)) positions of the COG for all vehicle driver combinations. The individual measured values are listed in Appendix B. Since the movements of the driver could not be considered with the setup shown, the center of gravity determined represents only one point of a possible range of center of gravity positions depending on the driver's movement. Studies such as [17] could be used in the future to determine the influence of motion on the center of gravity position for the vehicles considered herein in more detail. As can be seen in Figure 5, the center of gravity position in the longitudinal direction of the vehicle showed a high degree of dispersion, as expected, due to the design differences in seat position and wheelbase of the various vehicles. When considering the lateral center of gravity position, only minor deviations of the center of gravity from the center plane of the vehicle were observed under the static conditions of the test. The lateral center of gravity position tended toward negative values, which corresponds to a shift of the center of gravity toward the right side of the vehicle. This was caused by the drive components, such as chains and sprockets, which typically run on the right side of the vehicle. Figure 6 shows the determined longitudinal positions of the COG (\(l_{f}\)) in relation to the wheel base \(l\). In all vehicles, the COG was in the front half of the vehicle. The influence of the driver on the COG varied from vehicle to vehicle. This was partly due to the various options for adapting to the driver. Depending on the vehicle, this was done by adjusting the seat (strong influence on COG), adjusting the crankset (weak influence) or a combination of both. The empty mass also had an impact. The greater the empty mass of the vehicle, the less the effect of changes of the driver and their seat position. Figure 5: Measurement results for the COG longitudinal and lateral positions for all vehicles. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Vehicle** & **Drivers** & **Vehicle** & **Drivers** \\ \hline
1 & \(1,8,9\) & \(8\) & \(1,8,9\) \\
2 & \(1,8,9\) & \(9\) & \(1,4,5,6\) \\
3 & \(1,8,9\) & \(10\) & \(1,4,5,6,7\) \\
4 & \(1,2,3,8,9\) & \(11\) & \(1,4,5\) \\
5 & \(1,2,3\) & \(12\) & \(1,4,5\) \\
6 & \(1,2,3\) & \(13\) & \(1,4,5\) \\
7 & \(1,2,9\) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Measured vehicle-driver combinations. As mentioned, the center of gravity must be in the front third of a 2F1R vehicle for stable handling. As shown in Figure 6, not all vehicles met this stability criterion. Vehicles 1 to 7 were in the stable range (note that vehicle 2 had 4 wheels and was therefore stable in a wider range). Vehicle 4 was only just in the stable range, so unfavorable payloads could also result in an oversteering driving behavior. Similarly, the longitudinal COG position of vehicle 8 might have been below or above the stability limit, depending on the driver, so oversteering behavior might have also resulted here. The oversteering vehicles might have become unstable above the critical speed. Table 4 provides the understeer coefficient and ranges of the characteristic or critical speed for the different vehicle combinations using Equations (10) and (11). The cornering stiffness curve provided in Appendix C was used for the calculation. The curve was based on measurements of a bicycle tire under different wheel loads on a real road surface. It was assumed that the vehicles had the same tires on the front and rear axle. Equations (10) and (11) show that characteristic and critical speeds are inversely proportional to the understeer gradient \(K\). Thus, a small understeer gradient results in high values of critical or characteristic velocity.