What technical modification to a motorbike will generally void the issued operating licence?

In German traffic regulations, the operating licence (also known as the vehicle registration certificate) is based on the vehicle's original technical specifications. Any modifications that affect the fundamental performance or safety characteristics of the motorcycle can void this licence. Specifically, changing the gear ratio of the pinion and chain wheel alters the drive mechanism, which impacts the bike's performance and speed. Similarly, changing the engine power directly affects the vehicle's capabilities and compliance with its registered classification. Both require approval and re-certification to ensure safety and legality. In contrast, installing a tankbag is an accessory change that does not affect the technical approval or operating licence because it does not change any technical or performance-related specifications of the bike. Therefore, only changes that modify core mechanical features such as gear ratios or engine power generally void the operating licence unless properly approved.