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Motorcycle
Frames
See also
Engines
- Stroke, 2 or 4
- Configuration
Frames
- Introduction
- Types
Suspension
and Steering
- Girder front end
- Telescopic forks
- Hub center steering
- Steering dampers
- Rear Shocks |
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Frames
Motorcycle frames are usually made from welded aluminium,
steel or alloy, carbon-fibre is used in some expensive
or custom frames. The purpose of a motorcycles frame
is to act as a base onto which all the various components
can be bolted to. The engine generally sits inside the
frame, the rear swingarm is attached by a pivot bolt
(allowing the suspension to move) and the front forks
are attached to the front of the frame. The frame can
also help to protect the more sensitive parts of a motorcycle
in a crash.
Buell, one of the motorcycling world's greatest innovators,
uses the frame as a fuel tank on many of it's models
like the XB12S
Lightning.
The various types of frame commonly used include.
Single cradle frame. The
single cradle is the simplest type of motorcycle frame,
and looks similar to the first ever motorcycle frames.
It is made from steel tubes that surround the engine
with a main tube above and other, smaller diameter tubes
beneath. If a single cradle becomes double at the exhaust,
as frequently occurs, it is referred to as a split single
cradle frame. Single cradle frames are usually found
in off-road motorcycles.
Double cradle frame. Double
cradle frames are descended from single cradle frames.
They consist of two cradles that support the engine
one either side. Double cradle frames are commonly used
in custom motorcycles and simpler road bikes. They offer
a good compromise between rigidity, strength and lightness,
though they have now been technically surpassed by perimeter
frames.
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Backbone
frame. Far from the most desirable frame around,
the backbone frame comprises a single, wide main beam
from which the engine is suspended. The backbone frame
allows for great flexibility in design, since it is
concealed inside the finished motorcycle. The engine
just seems to hang in mid air. It is simple and cheap
to make, and is used mainly on naked and off-road motorcycles.
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Perimeter
frame. Motorcycle racing research has shown that
major advantages are to be gained in terms of rigidity
by joining the steering head to the swingarm in as short
a distance as possible. Flexure and torsion are dramatically
reduced. This is the concept behind the perimeter frame.
Two robust beams descend in the most direct way possible
from the steering head to the swingarm, passing around
the engine. The earliest perimeter frames were made
from steel, but the need to improve rigidity to weight
ratios led most manufacturers to adopt aluminium instead.
Aluminium is now by far the most common road bike frame
material and the aluminium perimeter frame is the most
popular frame for modern supersports motorcycles.
monocoque
frame. The monocoque frame is used nearly exclusively
on competition bikes and is very rarely found on road-going
bikes. Monocoque frames act as a single piece unit that
functions as seat mounting, tank and tail section. Though
they offer certain advantages in terms of rigidity,
monocoque frames are heavy and generally not worth the
effort.
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Trellis
frame. The trellis frame rivals the aluminium
perimeter frame for rigidity and weight. A favorite
of Italian and European manufacturers it has proved
a great success in racing and competition. The Trellis
frame uses the same principles as the perimeter frame,
and connects the steering head and swingarm as directly
as possible. The frame is made up of a large number
of short steel (or aluminium) tubes welded together
to form a trellis. The trellis frame is not only easy
to manufacture but extremely strong as well. The frame
pictures is from the Suzuki
SV650S.
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