Why do Bullets make DUBU-DUBU sound? | Let’s Make Education Simple

Why Bullet makes DUBU-DUBU sound

Why Bullet makes DUBU-DUBU sound? | Unnoticed 2.0 | Tamil | LMES

LMES (Let’s Make Education Simple) has the goal of revolutionizing the educational system in our nation and believes that learning should be enjoyable for all students.

LMES began via social media (Pepul, YouTube, and Facebook) by delivering short video blogs explaining science and engineering concepts of varying difficulty levels using their practical real-world applications.

Although there are wide varieties of two-wheelers like KTM, YAMAHA, PULSAR, and Royal Enfield.

Royal Enfield is always called Evergreen mass. Apart from the majestic looks of Royal Enfield, many of our Indians buy Royal Enfield Bullet for the ‘DUBU-DUBU’ sound when riding this bike. 

Ever thought why this sound is heard in such bikes?

Let’s check this out!

4 Stroke Engine

Although there are different types of bikes in the world, what is common in all bikes is the engine. Recently 4 stroke engines is used in bikes. It can also be called 4 cycle engine.

When we start our bike, the piston inside the engine moves downwards, and at the same time, the inlet valve inside the engine opens. From this inlet valve, fuel and air mixture enters the engine.

After this, the fuel and air mixture is pushed upwards in the piston engine. When this pressure is applied, fuel and air compress terribly. The spark plug above the engine will create the spark in that compress.

Now, the fuel and air mixture turns into fire. The pressure caused by this causes the piston to move downwards. Finally, the exhaust valve opens. The smoke in the engine is discharged through this exhaust valve.

Since this cycle takes place in 4 stages, it is called 4 stroke engine or 4-cycle engine.

Although 4 stroke engine is used in many bikes, the engine design will change for each bike. For example, an engine has a combustion chamber above the piston. The width of the combustion chamber is called Bore. Height is called a stroke.

Short stroke engine

For example, in bikes like Pulsar, the height of the stroke is less than the width of the bore. This is called a Short stroke engine.

Long stroke engine

However, the height of the stroke is greater than the width of the bore in the Royal Enfield bike engine. This is called a long-stroke engine.


Long stroke engine is said to be a major reason for Royal Enfield Bullet’s DUBU-DUBU sound.

Watch the full video to understand the process with live examples!

Generally, the piston in a short-stroke engine rotates very fast. Thus, because it spins so fast, the smoke from it is pushed out through the silencer very quickly.

This means that the piston in the long-stroke engine of the Royal Enfield Bullet rotates at a moderate speed. Thus, it rotates at a moderate speed leaving the smoke from it and pushing it out through the silencer. This is why you hear the sound of DUBU-DUBU in Bullet.

The engine is not the only reason for this DUBU-DUBU sound, the design of the silencer is also a reason.

As per India’s Motor Vehicle Act, the noise should not be above 80 decibels. Royal Enfield has updated the DUBU-DUBU noise a bit. This is a slight change from the DUBU-DUBU sound of the old Bullet.

Definitely, we will miss our grandfather’s Bullet a lot.