Proficient Motorcycling
BOB RECENTLY BOUGHT a
brand-new cruiser after
several years away from
motorcycling. Unfortunately,
Bob has had several
close calls in the short time he’s owned
his bike. His friends suggest that he install
some loud pipes to help him stand out in
traffic and make his presence known to
those inattentive drivers who don’t seem to
notice him. Bob’s friends also inform him
that loud pipes will convey a more aggressive
attitude, discouraging people from
“messing” with him.
These arguments make sense to Bob, so
he decides to install some loud aftermarket
exhaust pipes. But Bob’s first ride with the
new pipes installed stirs some mixed feelings
within him. On the one hand, he feels
more conspicuous in traffic, but he’s also
embarrassed at times by the loud noise.
Loud exhausts have been a part of motorcycling
for many years. Motorcyclists have
modified or replaced stock exhaust systems
since the early days to improve performance,
enhance the “tough-guy” image, or
simply to boost the motorcycle’s visceral
sensations. Some riders also believe that
loud pipes are a safety feature that warns
drivers of a motorcyclist’s presence and
helps to avoid a collision. This view is
summed up by the often-heard statement;
“loud pipes save lives.”
But not all agree with this philosophy.
The quiet bike proponents argue that
exhaust noise is an unreliable collision
deterrent. Some even perceive the “loud
pipes save lives” issue as merely a defensive
ploy to justify an anti-social behavior, rather
than a legitimate safety issue. In this installment,
we’ll attempt to shed some light on
the claim that loud pipes enhance safety,
and add some insight on how noise risks the
future of motorcycling.
Decibels
Scientists use the decibel (dB) scale to
measure sound intensity (loudness). The
decibel scale is often “filtered” to correlate
with human hearing. The “a” contour filter
is most commonly used and is described as
dBA. The human threshold of hearing (the
faintest sound heard by humans) is given
the value of 0. Because the human ear can
detect a very wide range of sound intensity,
the decibel scale is based on the power or
multiples of 10. A 10dB sound is 10 times
louder than the threshold of hearing, and a
20dB sound is 100 times louder. An example
of a 10dB sound is the rustling of leaves.
A mosquito’s buzz at close range is about
40dB. Normal conversation is roughly 60
dB, or 100 times louder than the sound of
the mosquito. A Kawasaki Vulcan 1500
produces about 80dB in stock trim in standardized
tests. The same motorcycle rolling
by with an aftermarket pipe produces
between 90dB and 95dB, making the aftermarket
pipe, at minimum, more than 10
times louder than the stock unit.
Conspicuity
In common situations, sound can be an
effective device for warning others of our
presence. For instance, we might command
someone to “watch out” if they are about
to step on our toes, or say, “excuse me, coming
through,” to someone in our way. But
sound has its limitations as a way of getting
attention. We all know that it can be hard to
get the attention of a person who is deep in
thought, distracted by conversation, or deafened
by the noise of a loud party. Loud
pipes can work the same way. Noise from a
motorcycle’s exhaust can make drivers
aware of a motorcycle’s presence, but are
likely to be effective only in lower speed
situations when road and wind noise are at
a minimum. Automobile manufacturers are
very aware of the intrusion of outside noise,
and take steps to insulate the “cabin.”
Increased speeds, noise of a moderately
loud radio, distraction of a voice chattering
on a cell phone, or even the whir of an air
conditioning fan can make it very difficult
for a driver to hear outside noises.
Pitch and Direction
Even though you can make your presence
known by making a loud noise, it’s
also important for the intended receiver to be in a position to hear you. If they are not then all the noise your loud exhaust system is producing is going to be of little use as a warning of your presence.