Why are motorcycles so loud?
The short answer
Motorcycles generally are loud because there isn't a ton of room to add noise-reducing design elements or equipment. Some motorcycles are even louder because riders change the stock exhaust system with one that is intentionally less muted. This is why some motorcycles are louder than cars and why motorbikes can be so noisy.
The long answer
VRROOOOOOM!!!
Motorcycles are loud. But what is it about motorcycles that makes them loud and why do (some) motorcyclists like it that way?
First, I'll get this out of the way. Not all motorcycles are loud. Newer motorcycles, ones with smaller engines, and electric motorcycles produce relatively quiet amounts of noise.
Generally though, motorcycles produce 65-80 dB of noise while idling and can reach 100-115 dB at full throttle. In comparison, the average car hits around 35-45 dB while idling and 50-60 dB at highway speeds. In other words, motorcycles can be louder than cars in typical situations.
There are four key reasons to explain why motorcycles are quite noisy.
Reason #1: Motorcycle exhaust systems are small.
Noise from cars and motorcycles both come from the vehicles' engines. But, as you may have noticed, motorcycles are smaller than cars. So, their exhaust systems are smaller too.
Diagram of a car exhaust system. Image sourced from CarParts.com.
Diagram of a motorcycle exhaust system, with yellow emphasis by me. Image sourced from Cycle World.
The smaller and less complex design of motorcycle exhaust systems means there's less opportunity for the air rushing through the 3-4ft pipe to slow down or get absorbed through the machine. This contributes to why motorcycles are so loud.
Reason #2: Motorcycles don't have room for bulky mufflers.
Similarly, the compact size of a motorcycle leaves little room for equipment that can dampen the engine noise. Adding a muffler to a motorcycle exhaust system reduces noise, but its impact is limited due to the small size required for motorcycles. This is why some people wonder, "Do motorcycles even have mufflers?" and why they often appear not to have effective noise reduction.
Reason #3: Motorcycle engines are exposed.
Unlike cars, motorcycles' engines and exhaust systems are exposed. You don't need to pop a hood to locate a motorcycle engine – it's just there. Without a closed compartment, there is zero barrier between the engine and the outside world that hears the bike go rushing by. This exposure contributes to why motorcycles are loud compared to cars.
Reason #4: Some motorcyclists swap stock exhaust systems for louder ones intentionally.
Despite noise regulations, some riders have decided to go the extra mile and make them louder on purpose. They do this by replacing factory exhaust systems with straight pipes. These pipes barely mute the noise.
Why? Some riders simply just like them louder for the sake of being loud (in other words, it's a vibe). Others claim it's for safety: They surmise that if the bike is louder, car drivers will be more likely to notice the motorcyclist which will reduce the likelihood of an accident.
"Loud pipes save lives" is more likely myth than fact because of how insulated cars are built. A 2021 study done in Romania found that at 33 ft behind the car, "even the noisiest motorcycles tested can hardly be heard inside the car." At that point, it's likely not enough time for the car to react safely. This challenges the perception of why motorcycles have to be so loud for safety reasons.
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Sources
Baron, L. (2020, February 5). 6 Main Reasons Why Motorcycles are so Loud. Soundproof Advice. https://soundproofadvice.com/why-motorcycles-are-so-loud/
Bobbly, E. (2022, July 23). Why Are Motorcycles So Loud?. Timeless2Wheels. https://bettersoundproofing.com/why-are-motorcycles-so-loud/
De Koning, S. (n.d.). Why are motorcycles so loud? Here’s all you need to know. Loop Earplugs. https://www.loopearplugs.com/blogs/blog/why-are-motorcycles-so-loud
Melissa. (2015, November 24). Why Are Harley-Davidson Motorcycles So Loud?. Today I Found Out. https://www.todayifoundout.com/index.php/2015/11/harley-davidson-motorcycles-loud/
Vaughn, M. (2021, March 26). Do Loud Pipes Really Save Lives? No. Autoweek. https://www.autoweek.com/news/industry-news/a35952569/loud-pipes-do-not-save-lives/
Why Are Motorcycles So Loud? [How Loud is Too Loud?]. PowerSportsGuide. (2021, October 8). https://powersportsguide.com/why-are-motorcycles-so-loud/
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