Yamaha YZ450FA 2011, Owner'S Service Manual

Page: 310 / 318

8-1
CHASSIS
TUNING
CHASSIS
SELECTION OF THE SECONDARY
REDUCTION RATIO (SPROCKET)
<Requirement for selection of secondary gear
reduction ratio>
• It is generally said that the secondary gear ra-
tio should be reduced for a longer straight por-
tion of a speed course and should be
increased for a course with many corners. Ac-
tually, however, as the speed depends on the
ground condition of the day of the race, be
sure to run through the circuit to set the ma-
chine suitable for the entire course.
• In actuality, it is very difficult to achieve set-
tings suitable for the entire course and some
settings may be sacrificed. Thus, the settings
should be matched to the portion of the
course that has the greatest effect on the race
result. In such a case, run through the entire
course while making notes of lap times to find
the best balance; then, determine the second-
ary reduction ratio.
• If a course has a long straight portion where a
machine can run at maximum speed, the ma-
chine is generally set such that it can develop
its maximum revolutions toward the end of the
straight line, with care taken to avoid the en-
gine over-revving.
Riding technique varies from rider to rider and
the performance of a machine also vary from
machine to machine. Therefore, do not imitate
other rider's settings from the beginning but
choose your own setting according to the level
of your riding technique.
DRIVE AND REAR WHEEL SPROCKETS
SETTING PARTS
Secondary reduction ratio = Number of
rear wheel sprocket teeth/Number of
drive sprocket teeth
Standard secondary re-
duction ratio 48/13 (3.692)
* 49/13 (3.769)
* Except for USA and CDN
Part name Size Part number
Drive sprocket "1"
(STD) 13T 9383E-13233
Rear wheel
sprocket "2"
47T 17D-25447-50
(STD) 48T 17D-25448-50
* (STD) 49T 17D-25449-50
50T 17D-25450-50
51T 17D-25451-50
52T 17D-25452-50
* Except for USA and CDN