Ask any Bullet rider what he loves most about the bike and 90% of them will say it is the thumping sound. The sound is equated to the heart beat and resonates with the riders in that manner. A Bullet without its sound is a washout and no charm at all.
Science behind the sound:
So how does a Bullet makes its characteristic sound? According to experts, the long stroke, large cubic capacity and low (comparatively) RPM of a Royal Enfield motorcycle produces a signature exhaust note. To this people attach aftermarket exhaust systems which increases the noise.
Your service engineer will tell you that the characteristic thump of the Enfield Bullet is due to its long stroke, low revving, large single cylinder engines, with a very clearly notable excavation beat of engine gases, through its exhaust.
With the Bullet, you get high torque and relatively low BHP – Brake Horse Power. The higher torque is due to the long stroke of its single cylinder engine. It uses this high torque to overcome rolling friction, so at lower revolutions, you can count the beats of this “thumping”, because it is sending out less frequent excavations of a large amount of exhaust fumes, rather than a steady stream of smaller excavations like in a car or a multiple cylinder motorcycle.
Sound engineering: Many Bullet riders will go to extra lengths to modify the silencer to get a particular sound popularly called the ‘Indori pataka’ in some parts of the country. The Indori pataka is a firecracker sound used to make a statement and grab attention on the road by some. The other sound stunt is the silencer blast which is popular with some riders. Riding on high speed the engine is switched off and then on to get a high decibel sound. This is done on sports bikes.
Attracting attention: Creating a stir on the road is all very well, but would you want to attract the wrong kind of attention. It would be wise to read up on the law on such modifications before you go ahead with it, as it can get you into trouble. Traffic police can stop and check bikes for silencer modification.
Traffic police are now armed with sound meters that can gauge the noise levels. A bike with a modified silencer can make a sound of 93 decibels normally but on full throttle this can zoom up to 107 decibels.
Lowdown on limits: The rules say that a bike sound must not exceed 85 decibels. This is equivalent to a propeller plane flyover, car wash at 20ft, food blender or milling machine. A quiet residential colony will have an ambient noise level of only 50 decibels, so you can imagine how loud your bike sounds.
There are media reports about noise pollution from bikes from various parts of the country including cities like Bangalore, Amritsar and Pune. In all three cities the riders has been booked for noise pollution under the Motor Vehicles Act section 190 (2). The bike is impounded and kept at the PS for at least five days. It is returned after much groveling and paying the fine of anywhere upto Rs 2500. Citizens have been clamouring for a ban on these bikes as it has become a public nuisance.
Traffic police are also cracking down on garage owners who are modifying silencers on these bikes. Currently the crackdown is on Royal Enfield bikes, but the lookout on other bikes is also on. So if you are thinking of tinkering with the dB killers in your silencer, think again.