Despite the above, there are legal restrictions on just how loud the bike, or any motor vehicle for that matter, can be. For instance, New York State law says the limit is 86 decibels above 35 mph when measured from 50 feet away. Different states have different laws, but this is pretty standard.
1. Less muffler equals more horsepower.
Generally speaking, mufflers restrict the rapid removal of exhaust from the engine, robbing the engine's potential to develop power. This, along with other more technical reasons, are why owners of any motor vehicle will alter the factory-installed muffler and exhaust. Depending on the modification, there can be a gain of horse power, enabling the Riders to go faster or carry heavier loads. Some modifications result in less.
2. It makes some Riders feel safer.
Motorcycles can be hard to see. In order to counter this, some feel that if the motorcycle is very loud then others on the road will be more aware of their presence. The saying is "Loud Pipes Save Lives!" There is great debate in the motorcycle world about this idea though. For one thing, the sound is louder to the rear of the motorcycle because of the megaphone effect. How many times have you not heard a motorcycle until it is going right past you? To some this proves that the idea is wrong.
Others that ride more conservatively believe that hearing the motorcycle in traffic or at an intersection is very effective in preventing collisions. They believe that Drivers are so bad at seeing motorcycles riding along with traffic that they need to be alerted to the presence of a motorcycle near them by the sound. But then again, car stereos and super quiet car interiors can negate this as well. For these reasons and others the American Motorcyclists Association counters with "Loud Pipes Risk Rights." Many Riders agree, many don't. Anyway, it is certainly a good way to get a few points while playing Count Motorcycles.
3. Love of the sound.
This is what you always suspected, isn't it? Well it's true. As much as we can argue about how safe a loud engine makes us feel, they really do sound cool to a great many people. In fact, Harley Davidson tried to patent the sound that their engines make. It was refused by the patent office, but isn't it interesting that for all Harley Davidson is known for, they felt the sound of the engine needed to protected by law. The SOUND is one thing though, the actual volume - the LOUDNESS - of the exhaust, is another. This must be adjusted to a legal specification or else the a manufacturer can't sell it on the showroom floor. Those ear-splitting noise levels you hear on motorcycles are the result of the owner's tinkering after purchase more than that of the factory production.