## 4 Summary and Discussion  
It is known from the literature that the mass properties have a significant influence on the vehicle dynamics and are necessary for vehicle dynamics modeling and the development of assistance systems. As a basis for corresponding investigations, this study examined a larger number of non-conventional three-wheeled bicycle vehicles in terms of their mass properties. The measurement of the centers of gravity was based on a method frequently used in vehicle technology via the determination of wheel loads. In contrast to the method used by [PERSON] et al. [17] for dynamic determination of the center of gravity position, only static measurements could be performed in this case. The center of gravity values determined thus represent only one point in a possible range of center of gravity \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{5}{c}{**With Intercept**} & \multicolumn{5}{c}{**Without Intercept**} \\ \hline \# of & **Model** & **Model** & **Model** & **Adj. R\({}^{2}\)** & **RMSE** \\
**Para-Meters** & **[Parameter Values]** & **Adj. R\({}^{2}\)** & **RMSE** & **[Parameter Values]** & **Adj. R\({}^{2}\)** & **RMSE** \\ \hline
1 & & - & - & \(l_{z}=c_{1}L\) & 0.53 & 4.89 \\
2 & \(l_{z}=c_{1}+c_{2}L\) & 0.61 & 4.47 & \(l_{z}=c_{1}L+c_{2}m_{e}\) & 0.64 & 4.27 \\
3 & \(l_{z}=-c_{1}+c_{2}L+c_{3}mL_{e}\) & 0.75 & 3.58 & \(l_{z}=c_{1}L+c_{2}m_{e}+c_{3}mL_{e}\) & 0.77 & 3.40 \\
4 & \(l_{z}=c_{1}+c_{2}l+c_{3}L+c_{4}m_{e}\) & 0.88 & 2.44 & \(l_{z}=c_{1}L+c_{2}m_{e}+c_{3}L+c_{4}mL_{e}\) & 0.85 & 2.81 \\
5 & \(l_{z}=c_{1}+c_{2}L+c_{3}m_{e}+c_{4}m_{e}+c_{5}l_{k}\) & \([-33.99,8.33,0.40,0.14,18.10]\) & 0.91 & 2.14 & \(l_{z}=c_{1}L+c_{2}m_{e}+c_{3}m_{e}+c_{4}L_{b}+c_{5}Lm_{e}\) & 0.94 & 1.82 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Formulae and results of stepwise regression for the group of all vehicles. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Nr.**} & **Model** & **All Vehicles** & **Tikkes** & **Velombies** \\  & & **[_n = 39_]** & **[_n = 9_]** & **[_n = 30 (27)_]** \\ \hline
1 & \(l_{z}=c_{1}(m_{e}+m_{d})l^{2}\) & \(c_{1}=0.136\) & \(c_{1}=0.112\) & \(c_{1}=0.140\) (\(c_{1}=0.138\)) \\
2 & \(l_{z}=c_{1}(m_{e}+m_{d})l^{2}\) & \(c_{2}=0.147\) & \(c_{1}=0.140\) & \(c_{1}=0.165\) (\(c_{1}=0.157\)) \\  & & \(c_{2}=1.727\) & \(c_{2}=0.916\) & \(c_{2}=1.463\) (\(c_{2}=1.609\)) \\
3 & \(l_{z}=c_{1}(m_{e}+m_{d})lL\) & \(c_{1}=0.071\) & \(c_{1}=0.070\) & \(c_{1}=0.071\) (\(c_{1}=0.071\)) \\
4 & \(l_{z}=c_{1}(m_{e}+m_{d})l_{f}l_{r}\) & \(c_{1}=0.631\) & \(c_{1}=0.479\) & \(c_{1}=0.663\) (\(c_{1}=0.659\)) \\  & & \(c_{1}=0.259\) & \(c_{1}=0.155\) & \(c_{1}=0.244\) (\(c_{1}=0.251\)) \\  & & \(c_{2}=0.147\) & \(c_{2}=0.142\) & \(c_{2}=0.173\) (\(c_{2}=0.164\)) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Parameter values (for the purpose of simplicity, the unit of the respective parameters is not displayed, SI units apply to all calculations). Values in parentheses apply to the velombies without the four-wheeled vehicle. coordinates in dependence of the driver movement. The static investigations showed that the vehicles were rather front-heavy and mostly stable according to the stability criterion in [26]. Some of the vehicle-driver combinations exhibited oversteering and thus had a tendency toward unstable handling. However, investigations of the critical speed showed only slightly oversteering driving behavior for these vehicles, with the critical speed being outside the relevant range for this class of vehicle. Based on the determined center of gravity heights and the corresponding values of the static stability factors, it can be concluded that the vehicles investigated here had significantly lower static rollover stability compared with passenger cars (\(\approx\)0.6 vs \(>\)1.0). The investigation of the moments of inertias showed a stronger relative contribution of the vehicle to the total inertia in contrast to the total mass.