The first motorcycles were in fact just simply motorized bicycles that had engines attached to bike frames. Over the years they have developed into very complicated machines. Technology was put to work to increase control, fuel economy, speed and comfort. If you have a BMW motorcycle and you own the bike for an extended period of time, you are, at some point, going to need BMW motorcycle parts. You can buy new parts but second hand motorcycle parts are often just as good and are available at a much better price. All separate components have their own purposes, but they depend on the other parts around them.
A Small Lesson in Motorcycle Anatomy
The motorcycle chassis