Why are motorcycles so loud?

If you are often bothered by traffic noise, you’ve probably noticed that not all vehicles are equally noisy. Other than emergency vehicles blasting their sirens as they make their way through traffic, motorcycles tend to be some of the loudest vehicles on the road. But why are motorcycles so loud?

There are several reasons, but they usually always fall onto one of two categories:

1. The size of the vehicle – This might sound counterintuitive, but the bigger the vehicle the easier it is to silence it down.
2. The culture of motorbiking – For many motorbike owners their bike isn’t just a transportation method to get from A to B. Riding motorbikes can be a way of life, a culture, a community… and believe it or not engine noise is a big part of the identity of these communities, a statement, something to be proud of.

Why are motorcycles so much louder than cars?

When it comes to making a motorbike quieter, size matters.

Even though there are some electric models out there, most motorbikes still run on gasoline. That means they mount a combustion engine. Without going into a lot of detail about how a combustion engine works, the one thing that’s important to understand here is that combustion engines generate movement through explosions. Literal explosions. As in, mix gasoline with oxygen and light up a match kind of explosion.

Thousands of these controlled explosions happen every second, even when the vehicle is not moving. Crazy, right?

Anyway, as you can imagine, these explosions produce a significant amount of noise. So much noise that the levels on our streets and roads would not be even tolerable if it wasn’t for two other key pieces present in our cars and motorbikes: the muffler (also known as a silencer) and exhaust.

The noise produced by the engine explosions travels through the muffler and exhaust, which bring the volume down significantly before releasing it to the surroundings. The muffler and exhaust are quite bulky parts of the engine, and as a rule of thumb, the larger the muffler is the quieter the vehicle.

Motorbikes, of course, have a lot less space to mount these parts, thus making it a lot harder to silence down a motorbike engine than a car’s.

This does not mean manufacturers can’t build quieter motorbikes. Advanced engineering has managed to create smaller, yet highly efficient mufflers, but they don’t come cheap. They are usually heavier, come with a significantly higher price tag, or both, which results in them only being used by brands on very specific models.

Why are motor scooters louder than bigger motorbikes?

Still on the side of counterintuitive concepts, you might have noticed that smaller motor scooters, or mopeds, are often louder than larger motorbikes. But why is this?

A big part of it has to do with the concept we just covered in the previous section. Motor scooters are designed to be the smallest they can be, so they have the least space to mount their muffler and exhaust. They are often also seen as “cheap” vehicles, used mainly for deliveries and very short commutes. This means brands will take any opportunity they can to make them cheaper, as customers aren’t willing to pay for any extras.

But there is another reason why motorscooters are louder than bigger motorbikes, and that is the way these vehicles are driven. The law sets the maximum number of decibels a motor vehicle can produce. Motorbike makers then take that number and engineer the motorbike so that at its peak, when the vehicle is the noisiest, it doesn’t go over that limit. I’m sure this won’t come as a surprise, but that noise pick happens when the vehicle is accelerating as quickly as it possibly can.

Well, because mopeds and scooters have such small engines you usually have to twist the throttle to its maximum every time you want to get it moving. Imagine you have stopped at a traffic light and the light turns green. In your car, you’ll probably press the throttle pedal 15-20%, but on a scooter, you’ll twist it to its maximum. That means every single time you will be asking 100% of the engine, which of course produces more noise than asking 20% of it.

This non-progressive, on/off type of driving is the noisiest possible. This is also true for larger motorbikes, even for cars, but with more powerful engines you will never accelerate to the maximum at a traffic light. Not only you don’t need to, but it can also be dangerous, whereas when a moped does it you will just see it start to move relatively slow, while making a lot of noise.

Why do riders want their motorbikes to be noisy?

As mentioned earlier, riding a motorbike is rarely just a matter of getting from point A to point B. Motorbikes are not that practical when you think about it. You cannot carry much with you, you don’t have heating or AC, you need a ton of geat to be safe… so why is it that people still seem to love their motorbikes?

It’s a culture, an experience. Riding a motorbike is a one-of-a-kind experience. There is a sense of freedom to it, of lightness, power… the same thing that scares some is what gets others hooked, always wanting more.

Think about it, you are driving a vehicle that’s usually under 400 pounds and has anywhere between 80 to 130 horsepower (some go up to over 200HP), the air on your skin, your weight controlling where the motorbike goes… it is quite an experience, kind of like riding a rollercoaster but with no rails, you are in control.

An average car can weigh 4000 pounds and have around 150HP. The feeling of acceleration you can get on an average car is nothing compared to what you’ll feel on a motorbike. The feeling of how powerful the machine under you is cannot be compared. And part of feeling how powerful the machine is has to do with the noise and the vibrations produced by the engine.

These side-products of any combustion engine, which manufacturers usually try to avoid in street cars, are something motorbike users often look forward to, and therefore something that manufacturers try to maintain. For some iconic brands like Harley Davidson, Ducati, or BMW the sound of their engine has even become a signature of their brands, recognized by fans every time one of their vehicles passes by.

At this point you might find yourself thinking “I understand, but there is no way a motorbike that loud is legal”. And you might be right. Some motorbike owners feel like the legal sound their vehicles produce is not enough, and decide to modify their mufflers and exhausts to change the tone of its sound, and in many cases, also increase their volume. This is illegal and can be fined, as we will see in the next section.

What does the law say about noisy motorbikes?

Ok, but does the hobby of a few justify the annoyance of many? What does the law say about it?

Well, no, of course not. No motorbike manufacturer is above the law. Any motorbike they put out on the streets has to comply with whatever regulation exists in the state where they are sold.

Each state has slightly different regulations regarding this, which you can check in detail here. However, most of them say similar things, and can be summed up as:

• Modifying mufflers or exhausts is illegal in most states.
• The maximum dB reading for any circulating motor vehicle (motorbike or car) is 80db from 50 feet away.
• At a standing test, the maximum dB reading from 75 inches away is 95db.

States are becoming increasingly aware of the problems loud vehicles cause, and are passing stricter laws to ensure that noise levels remain reasonable. As an example, the state of NY passed a new law in April 2021 increasing the fines for those driving excessively loud motorbikes as well as for anyone offering to sell or install devices to modify the normal functioning of mufflers. In the state of NY driving an excessively loud motorbike can be fined with up to $500 and 30 days imprisonment, whereas modifying mufflers can be fined with up to $1000 and 30 days imprisonment.