There are several reasons why a motorcycle is louder than other vehicles.
The first thing to realize is that, unlike a car, most motorcycles do not have all-enveloping bodywork to contain the mechanical noise. Other sounds such as the muffler and chain drive add to the overall noise level.
Second, motorcyclists like nothing more than tinkering and modifying their bikes, and a louder muffler is one of the most popular and straightforward modifications.
Lack of Bodywork
Unlike cars, motorcycles generally don’t have engine compartments to lock in the noise. There are some exceptions, where the bodywork almost wholly encloses the engine, but these are few and far between.
A lot is going on inside your motorcycle engine. Pistons move up and down at high speeds, rotating camshafts and gears driven by cam chains plus regular explosions to ignite the fuel.
Manufacturers work extremely hard to minimize and contain all these mechanical noises, but it is challenging.
Short Muffler
Space is limited on a motorcycle, and this includes room for the muffler, which needs to reduce the noise while still allowing the engine to function correctly.
Other vehicles, such as cars, and trucks, will sometimes use multiple mufflers, but this isn’t an option on most motorcycles.
To overcome these limitations, manufacturers must make the muffler very restrictive, but this can reduce the efficiency and ultimately the power of the motorcycle. It is a balancing act that motorcycle manufacturers are constantly working on.
If you have ever been to a motorcycle race day, you’ll have noticed how exceptionally loud race bikes can be. Race bikes have little noise control, and the muffler pipes are tuned to produce the best power characteristics.
Aftermarket muffler
As a biker, tuning or modifying our motorcycles is all part of the enjoyment, and one of the most popular changes is to swap the muffler. There are various reasons for this: making your motorcycle louder, increasing the engine power, or wanting to be noticed as you ride past.
Aftermarket mufflers come in all shapes and sizes. Some are very well engineered, adding power as well as more noise, while others simply improve the looks and sound of the motorcycle.
New versus Old Motorcycles
There are two main reasons a new motorcycle will be quieter than an older bike. Technology is changing and improving, enabling manufacturers to produce quieter motorcycles, plus local government regulations have reduced the allowable noise level.
Motorcycle engine technology, and particularly muffler design, have improved massively in recent years. In addition, components such as mufflers are now lasting longer. An old muffler will allow more noise out than a newer one.
Rider Preference
People often ask why bikers like loud motorcycles. Every rider has his reasons, but in general, it’s one or more of the following.
Enjoyment
Many bikers simply like the sound their bike makes with a louder muffler. A more free-flowing muffler is louder, but it may also cause the engine to pop and bang a little. Backfiring, notably when shutting off the throttle, is a sound most bikers like.
Read more about what causes a motorcycle to backfire.
I have louder mufflers on my Suzuki SV1000S. It’s a 1000 cc V-twin and makes a deep rumbling sound when the revs are kept reasonably low. Push the revs higher, and it is louder, though.
Safety
Many bikers will argue that they are safer riding a noisy bike. It is true that the leading cause of many accidents between motorcycles and other vehicles is drivers that are unaware of the motorcycle.
I think we can all say that we witness inattentive drivers, and sometimes we get distracted while driving. A little bit of noise can certainly help to get a driver’s attention and possibly avoid a collision.
Also see: Do motorbikes have horns?
Performance
Replacement mufflers can improve the performance of your motorcycle, as well as make it louder. Of course, the opposite is also true, and a poorly designed aftermarket muffler can reduce the performance of your motorcycle.
For most slip-on mufflers, the difference is pretty small, and you’ll barely notice. However, a well-designed muffler and a tune-up on a dyno can give a good increase in power.
Noise Limits in the US
In common with most countries, the US has some laws on noise pollution. Any motorcycle produced since 1983 is subject to the Noise Control Act, setting limits for manufacturers. In addition, most cities and states have local ordinances on noise, although they do vary.
In general, a noise level of around 80 or 85 decibels is the acceptable limit. Anything over this, and you risk attracting the attention of law enforcement and getting a ticket.