The legality of using an aftermarket exhaust or silencer for a motorcycle can vary depending on the specific laws and regulations of your country, state, or region. In many places, there are regulations in place that dictate the acceptable noise levels for motorcycles, which are typically measured in decibels (dB).
Using an aftermarket exhaust or silencer can potentially alter the noise output of your motorcycle, and if the noise exceeds the legal limit, it may be considered illegal. Some jurisdictions have specific restrictions on modifying the exhaust system, while others have general noise regulations that apply to all vehicles, including motorcycles.
To determine the legality of using an aftermarket exhaust or silencer for your motorcycle, you should consult the relevant local traffic laws or consult with a knowledgeable authority in your area, such as a local law enforcement agency or a vehicle inspection authority. They can provide you with accurate information regarding the specific regulations that apply to your situation.