A motorcycles relatively simple design and availability of
replacement or accessory components make it easy, inexpensive and
popular to modify with unknown safety consequences.
Virtually every part of a motorcycle can be modified, and many modifications
can affect the safety of the vehicle. Modifications aimed at improving
or changing the way the machine works include those directed at
engine performance, comfort, handling, braking, or cargo capacity.
Some changes are made to personalize and customize the appearance.
Even seemingly simple, routine changessuch as fitting new
tirescan change a motorcycles handling.
Some changes (such as upgrading suspension components, tires,
or brake components) can be purely beneficial, while others can
be mostly detrimental from a functional standpoint. Many involve
trade-offs. For example, a motorcycle that is lowered to give
the rider a more surefooted stance at a stop gives up some cornering
ground clearance and suspension travel. Some changes, such as
major frame modifications or use of an aftermarket frame, can
change the entire character of the motorcycle. Installation of
a sidecar or a three-wheeled trike kit creates an
entirely different class of vehicle that no longer handles or
responds like a two-wheeled motorcycle.
Although trailers towed behind motorcycles have become more popular,
we know of no data that indicate their effect on motorcycle behavior.
Most motorcycle manufacturers warn against their use, however.
Users may install aftermarket components or make modifications
that their motorcycles were not designed for or tested with. They
may combine modifications that were not designed to be together
and when combined have unforeseen effects on the performance of
the vehicle. Riders may also fail to understand all the consequences
of a change. Some changes also lend themselves to misuse. Adding
a cargo compartment or a luggage rack at the rear of the motorcycle,
for example, may allow the user to place too much weight there
despite labels warning against it. A change in weight distribution
can significantly alter how a motorcycle handles.
The Hurt Report showed that modified vehicles were over-represented
in crashes. However, the types of vehicles created by the modifi-cations
specified in that studyknown then as semi-choppersnow
constitute the two largest subcategories of original equipment
street motorcycle: sportbikes and cruisers.
|Because a motorcycle created by an aftermarket or
user-created modification is much different than one built by a
manufacturer, the current situation has changed too much for that
aspect of the study to be relevant. The Hurt Report also
found street motorcycles with modified exhaust systems were over-represented
As with original equipment, the quality and safety of most aftermarket
components have steadily improved, although seemingly they havent
reached the levels of original equipment components yet. Users
have access to more information of such products from manufacturers
than in the past, and the user is likely to be better informed
of the possible drawbacks to the modification. The liability climate
has also made suppliers and installers more cautious about modifying
Some of the most questionable modifications that were popular
during the era the Hurt Report was conducted, such as removing
the front brake, have fallen out of style. It is not clear, therefore,
if modifications are still a significant factor in motorcycle
The modifications favored by motorcyclists change with technology,
fashion, and other factors, which makes most specific regulations
unfeasible. Some countries, such as Germany, require that prior
to any sale of a motorcycle, any of its modifications must be
tested and certified. Although this may prevent some crashes,
it may also cause some by limiting the riders access to
superior tires, brakes, suspension, and other components.
WE WANT TO BE
The current role of vehicle modifications in motorcycle crashes
should be better understood.
All aftermarket vendors should make safety a priority in the
development of motorcycle accessories.
TO GET THERE
Any future studies of crash causation should certainly examine the
role of modifications to motorcycles, particularly major changes
such as chassis modifications, sidecars, and trailers. Since some
alterations may be under-represented in motorcycle crashes, that
issue should also be addressed. Education of riders may be a better
approach to dealing with modification-related problems than regulations.