Frame/Body Panels Description - Honda Motorcycle Service Manual

FRAME/BODY PANELS
Motorcycle, scooter and ATV frames serve as a skeleton t o which all other components are attached. Various forms and
intensities of vibration and stress from both the engine and the suspension act against the frame when the vehicle is in use.
These forces are major factors in determining the final design of each frame.
The various frame designs can be classified into one of a few general categories. Certain types are chosen for particular
models according t o their engine displacement, the use the vehicle is designed for, serviceability, cost factors, and even
visual appeal.
The material used for a frame is chosen by similar means. Generally, aluminum frames are reserved exclusively for sport type,
on-road motorcycles, usually of middle-to-large engine displacement. Virtually all other frames are made of steel. Aluminum
alloys are lighter than steel of the same strength, but are bulkier and more expensive t o produce.
A wide variety of tubing and pressed steel shapes as well as castings and forgings are combined t o form the optimal
framework for a particular model.
Many of the earliest Honda models used primarily a round steel tube frame.
Later models up t o 305 cc used a frame made mostly or entirely of pressed steel plate.
Some of today's frames are made almost entirely of round steel tubing of various sizes and thicknesses. Others are made up
mainly of square steel tubing. Most aluminum frame members are some form of rectangular tubing, though a few pieces are
square. The highest stressed rectangular aluminum members are often relatively complex extrusions designed to fulfill a
specific set of requirements. Most aluminum and steel frames include some castings or pressed steel sections in order t o form
strong and compact tube joints, and for pivot or major attachment points.
Round tubing has the same strength in all directions. Square and rectangular tubing (as well as other variants) have different
strength characteristics in different directions. When the maximum strength is required in a vertical direction and the strength
in a horizontal direction is not as important, rectangular tubing w i t h greater strength in the areas needed is chosen. A t times a
frame is lightened by changing the combination of the types of tubing.
Thinwall rectangular aluminum tubing is strengthened by internal stiffening ribs and extrusion production. Some models use
a special modified pentagonal or hexagonal extruded aluminum tubing (with internal strengthening ribs) in order to improve
the frame member's strength to weight ratio, its rigidity in one or more specific directions, and in some cases, to allow a more
compact and unobstructed riding position.
The various material types, forms and dimensions used in frame design are linked directly t o the experience gained from
Honda's ongoing racing programs around the globe. As new knowledge is gained through competition, it is combined with in-
put from non-competition testing and utilized in the construction of each new generation of production machine.
STRONGEST-
WEAKER -
- -
-
RECTANGULAR MODIFIED HEXAGONAL
WEAKEST.
..
.
. .
EXTRUDED ALUMiNUM EXTRUDED ALUMINUM TUBING
RECTANGULAR TUBING
ROUND TUBING
@
STRENGTH EaUAL STRENGTH DIFFERENT
lN A L ~ D I R E ~ T l ~ ~ S
DEPENDING ON DIRECTION MODIFIED PE T M X N A L
OF FORCE APPLIED
EXTRUDED ALUMINUM TUBING
The frame also serves to absorb vibration from the engine and, to some degree, from the road surface. The difference in basic
frame structure
i s
determined according to the engine type and the type of use the machine is designed for.
Two only slightly different frame designs may have significantly different vibration absorbing or generating characteristics
which make one design correct and the other unsuitable, even with the same engine installed. Therefore, the particular frame
structure a machine ends up with is chosen according t o the engine type and by the specific use the machine is intended for,
in order to prevent unpleasent vibration t o the rider and premature fatigue to structural members.
Frames are classified as follows, according t o differences in basic structure:
Date of Issue : March, 1 9 9 5
0
HONDA MOTOR CO.,LTD.