In the informative series Today I Found Out, host Simon Whistler explains why Harley Davidson motorcycles are so famously loud, how customers modify their bikes to be even louder and how new laws are looking to dampen the noise.
Straight off the line today, Harley exhaust systems can emit noise as high as 80 decibels (dBs), give or take depending on the model. … That said, loud, powerful sounding engines have become a signature of this particular brand of motorcycle, leading to the real problem- many who buy Harleys are not satisfied with the legally regulated stock noise of the engine and instead choose to swap out the existing exhaust systems for straight pipes that don’t really mute the engine noise at all. This results in sound that can exceed 100 decibels when revved up. …Given this sort of extreme noise pollution, there has been a backlash against noisy bikes in recent years, with many local communities placing restrictions specifically on motorcycle noise, and others banning them altogether.