There is a very clear-cut answer to your question, and it is spelled out in the very front of the IATA Dangerous Goods Manual.

If an object has its own classification - for example, a motorcycle is classified as 'UN 3166 Vehicle, Flammable Liquid Powered' - then, you don't go any further into breaking the object down into all the different parts that it is composed of.

Flammable liquid powered vehicles (known as "cars and motorcycles" to the general public) contain all sorts of component parts that have their own DG classification if shipped separately. For example, batteries, pressurized gas shock absorbers, gasoline, lubricating oil, inflated pneumatic tires, just to name a few. But, none of those things are considered because they have already been considered when the classification 'UN 3166 Vehicle, Flammable Liquid Powered' was developed.

What you do need to do is go to the Packing Instruction for UN 3166 (Packing Instruction 900), where you will see that it says the gas tank can't be more than 1/4 full (that addresses the risk posed by the gasoline, a DG in its own right), and that the battery needs to be mounted in the vehicle manufacturer's original specification mount (that addresses the risk of electrolyte spillage from the battery, which is also a DG in its own right). There are no remarks or requirements about the lubricating oil, shock absorbers, or the pressurized rubber tires, because when the whole object (vehicle) is considered, those items don't require any special care or attention - even though they might if they were shipped as separate, individual objects.

Therefore you would not list or document 'gasoline' or 'battery' on a waybill or DG declaration when shipping a motorcycle - you only document the 'Vehicle, Flammable Liquid Powered' (the motorcycle) itself.

If your motorcycle has panniers (saddlebags), almost all carriers will allow you to put materials that directly support operation of the motorcycle (helmet, protective clothing, tools, reasonable spares) in the panniers provided none of the items in the pannier are DGs. For example, you could not put a spare battery in the panniers, or camping stove fuel, or stuff like that. Putting a spare shock absorber in the pannier is kind of borderline - super-strictly speaking, it is a DG, but I can't imagine anyone would object if there is another identical shock absorber installed on the motorcycle itself, less than a foot away from the pannier.

Hope that helps,

Michael