Why Are Harleys So Loud?

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Most Harley-Davidsons come off the factory line at around 80 decibels. This is considered average for a motorcycle, so what’s with their loud reputation?

Motorcycles are about 20 decibels louder than a car and are louder than most everyday sounds, but they’re not obnoxiously loud unless the owner wants them to be. Harley owners have gotten a reputation for being in that group of bikers who not only want to be seen but especially heard. While many people buy a motorcycle to feel the sound under their seat, there is a point of volume that is just too much.

While it’s true that motorcycles are loud, they aren’t ridiculously loud unless the owner wants it that way. But is it true that most Harleys are designed louder than others? What gives the average Harley owner the reputation for a truly deafening ride?

From aftermarket mufflers to the simple science of an uninsulated engine with a short exhaust pipe, motorcycles will be loud. But many believe that Harley-Davidson owners fall into that detested category of ALL CAP BIKERS  that need to be heard to be seen. So why are motorcycles loud and Harley bikes even louder? Let’s do a deep dive into the ear-drum-damaging decibel-boosting din that can literally leave you deaf.

I researched relevant sites to find the science behind the engine noise of a Harley-Davidson and looked behind the curtain at many bikers’ psychological motivation to ride obnoxiously noisy bikes by checking the latest forum sites. You might be surprised by the reputation vs. reality of Harley owners and their need for ear-splitting sound.

In this article...


The Danger Behind Loud Engines

Before we discover the science behind loud engines and the psychology of the biker modding his Harley to be even louder, we need to understand what strong vibrations do to the inner ear.

How Do We Hear?

Vibrations in the air create a sound that travels to the four parts of our ears. The outer ear (the oblong skin flap on the sides of our head) funnels these sound waves to our eardrum. The eardrum is comprised of three small bones in the middle ear that amplify the sound vibrations sending them to the inner ear. The inner ear is a fluid-filled receptor with tiny hair cells or “stereocilia” that bend with the vibration. The auditory nerve then carries the electrical signal to the brain.

The damage comes when the hair cells are bent over from high-decibel sounds and become inflexible and unusable temporarily. If the hair cells become too damaged, they die. This leads to the loss of hearing and the inability to hear nature like birds, streams, or music, or to communicate with your friends.

How Much Sound Vibration Is Too Much?

We measure sound in decibels. Every ten points of a decibel mean that the sound is ten times as loud. This scale will give you insight as to how loud is loud in decibels:

Decibels Example
10 Breathing
20 Cat Purring
30 Watch Ticking
40 Refridgerator Humming
50 Normal Conversation
60 Air Conditioner
70 Vacuum Cleaner
80 Freight Train
90 Boeing 737 at 1 mile
100 Boeing 737 at takeoff
110 Live Rock Band
120 Chain Saw
130 Emergency Sirens
140 Fireworks

The damage-inducing sound vibrations begin at 80 decibels after 2 hours of exposure, 90 decibels after 1 hour of exposure, 100 decibels after 15 minutes of exposure, 105 decibels after 5 minutes, and 110 decibels after just 2 minutes. Anything north of 110 can instantaneously damage your ear temporarily which has the potential to become permanent.

To prevent hearing loss not only to the motorcycle owner but to the wife, kids, and neighbors of the two-wheeled hobbyist, the EPA (environmental protection agency) has required the decibels of newer motorcycles to be under 80 decibels. Of course, older motorcycles like Harley Shovelheads and Panheads could be much louder. It’s actually illegal in most states to be louder than 80 decibels and city codes try to mitigate noise pollution from open-engined vehicles. The enforcement of such laws varies from community to community and is a hot topic of debate on both motorcycle forums and social media.

The Science Behind The Sound Of A Motorcycle Engine

The range of frequencies that an engine emits is based on the vibrations that come from the combustion chamber in each cylinder that explodes as the spark plug ignites the fuel and air mixture that is compressed by the piston over and over again, thousands of times a minute. As the RPMs (rotations per minute) increase, the number of small explosions increases, and the engine continues to get louder.

To muffle the sound, the exhaust fumes and noise travels through baffled pipes and a catalytic converter that helps clean the air and deaden the sound until it is finally discharged through the tail pipe. Because the engine is in the open air and the exhaust system is relatively short (4 to 6 feet) compared to a car (between 10 and 15 feet). This restricts the airflow of the motorcycle, and some people who want more horsepower and efficiency will shorten the exhaust, remove the baffles, and even remove the catalytic converter to allow the engine to “breathe” and become more powerful. This increases the noise substantially.

Harley-Davidson offers dozens of mufflers that all fall under the EPA’s noise regulations that both improve the look and the performance of the bike. Their Screamin’ Eagle High-Flow Street Cannon slip-on mufflers are works of art that also keep the sound under 80 decibels. However, many bikers aren’t interested in noise reduction but instead lean the other way. Motorcycle muffler websites are dedicated to increasing decibels to ear-bleeding levels and teach the observer how to drill holes in the exhaust, remove the muffler, baffles, catalytic converter, install straight pipes, and install after-market mods to shake and crack the foundation of your garage before you leave for work.

These mods may not be illegal to buy and install, but they are illegal to actually use if the engine roars above 80 decibels. Many of these can redline the decibel meter over 115. Enforcement is often determined by the budget of the police force and the number of complaints in the community, but the reason your flower pots fall off your windowsill to a thundering Harley on a Saturday morning is the lack of enforcement of this municipal ordinance.

The Harley Reputation for Loud Engines

There is no scientific data concerning the Harley-Davidson bike owner and their proclivity to loud engines. The long-standing rep of the scoff-law, leather-clad, German bike-helmeted Harley owner who revs his engine for five minutes every morning does not have any documented evidence that they represent the majority. In fact, today’s Harley owner cares about his neighbor’s ability to enjoy singing birds in the morning, and the exception to that only proves the rule.

Yes, you’ll still find the under-parented teenager or young biker that is hell-bent on ear destruction, but most, and I would say the vast majority, are against noise pollution. The distinctive sound of the Harley engine is a thing of beauty and a reason to purchase the legendary machine, but we Harley owners also know that just like an all-you-can-eat chili buffet, too much of a good thing is not a good thing. We can love our engines and our neighbors.

Anytime you hear a Harley owner say they are loud for safety in order to warn cars of their presence and are meanwhile rattling your mirrors and setting off car alarms as they rumble through the neighborhood, you should call your local law enforcement: the more calls, the more the response. Endangering people’s ear drums and preventing the sound of nature and conversations is poor Harley ambassadorship that needs to end with the next generation of H-D riders.