## 4 Discussion  
Literature shows that a forward leaned rider with stretched arms and hands on the handlebar have little influence on the self-stability behaviour of a bicycle while an upright rider position with flexed arms and hands on the handlebar changes the open-loop dynamics drastically, which results in a decreased self-stability [7]. Since the forward lean angle on the conventional bicycle is smaller (65\({}^{\circ}\) versus 70\({}^{\circ}\)) than on the electric one, a better self-stable behaviour is expected for the conventional bicycle. On the other hand, the difference in the forward lean is the result of a difference in the front frame assembly. [PERSON] concluded that the centre of gravity of the front frame assemble should be 9 cm in front of the steering axis, which is measured perpendicularly on the steer tube [12]. The centre of gravity of the front frame assembly of the electric bicycle is closer to the optimum described by [PERSON], which results in an enhanced self-stable behaviour of the electric bicycle. Since both systems counteract, only marginal differences are found between the conventional and electric bicycles. The self-stable mode of the conventional bicycle starts at a lower speed than the electric bicycles. Additionally, the complex conjugate pair is formed early, which causes a significantly smaller semi-stable range than the electric bicycles. The self-stable range is relatively small, even though the electric bicycle with the motor in the rear wheel and the battery pack in the luggage rack (configuration 3) performs worse. When considering the whole period, the bicycle is easy to stabilize. The conventional bicycle and the electric bicycle with the motor in the rear wheel and the battery pack in the luggage rack perform worse.  
Significant differences are found between the six electric bicycle configurations. Most notably, the semi-stable range is significantly higher for the electric bicycles with a motor in the front wheel. [PERSON] described the \"gyroscopic self-stabilization\" of a bicycle in 1868. The gyroscopic effect of a spinning front wheel increases the stability [13]. Currently, the idea is universally accepted in literature [14]. Addressing electric bicycles, the front wheel motor adds weight to the front wheel assembly, which increases the self-stabilization effect. When taking the self-stable range into account, the electric bicycle with a front wheel motor and a battery located in the lower mid-tube performed the best. Furthermore, this effect is observed for every bicycle configuration. When a battery is located in the lower mid-tube, the self-stable range is higher than when the battery is located in the luggage rack. [PERSON] discussed that the gyroscopic effect is only relevant for a light riderless bike, whereas a heavier cyclist overpowers the effect [4]. Similar to the influence of the cyclist's posture discussed by [PERSON] et al. [7], the differences could be assigned to the lower location of the centre of mass of the rear frame assembly due to the lower battery placement.  
Knowledge about the stability behaviour of common bicycles can improve bicycle design to increase the level of comfort of the cyclist. A low A and B value and a high C value is preferred to minimize the counteractions of the user and increase the bicycle stability. The study showed that motor and battery placement significantly influence the stability behaviour. However, it should be noted that cyclist weight and posture are equally important. For future work, different types of cyclists should be taken into account.