The legality of installing an aftermarket pipe on a Harley Davidson, or any motorcycle for that matter, can vary depending on the jurisdiction and local regulations. In many countries, there are laws and regulations that govern the noise emissions of motorcycles, including the exhaust system.
In the United States, for example, the Environmental Protection Agency (EPA) has established regulations that specify the maximum noise levels allowed for motorcycles. These regulations are enforced by state and local authorities. If an aftermarket exhaust system exceeds the noise limits set by the EPA or local regulations, it may be considered illegal.
Additionally, some countries or states have specific laws or regulations that require motorcycles to have certain types of exhaust systems or restrict the modification of stock exhaust systems. It's important to consult the specific laws and regulations of your jurisdiction to determine the legality of installing an aftermarket pipe on a Harley Davidson or any motorcycle.
It's worth noting that even if an aftermarket pipe is legal from an emissions or noise perspective, modifying the exhaust system may still have implications for warranty coverage and insurance policies. It's recommended to check with the motorcycle manufacturer, local authorities, and insurance providers to ensure compliance and avoid any potential issues.