Yamaha YZ 2017 Series, Owner'S Service Manual

Page: 390 / 410

CHASSIS
10-1
EASB29B387
CHASSIS
EASB29B388
SELECTION OF THE SECONDARY REDUC-
TION 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.
TIP
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.
EASB29B389
DRIVE AND REAR WHEEL SPROCKETS
SETTING PARTS
EASB29B390
TIRE PRESSURE
Tire pressure should be adjusted to suit the
road surface condition of the circuit.
• Under a rainy, a muddy, a sandy, or a slippery
condition, the tire pressure should be lower
for a larger area of contact with the road sur-
face.
Secondary reduction ratio = Number of
rear wheel sprocket teeth/Number of
drive sprocket teeth
Secondary reduction ratio
3.923 (51/13)
Part name Type Part number
Drive sprocket “1”
(STD) 13T 9383B-13218
Rear wheel
sprocket “2”
47T 17D-25447-50
48T 17D-25448-50
49T 17D-25449-50
50T 17D-25450-50
(STD) 51T 17D-25451-50
52T 17D-25452-50
Standard tire pressure
100 kPa (1.00 kgf/cm
2
,15 psi)
Extent of adjustment
60–80 kPa (0.60–0.80 kgf/cm
2
,
9–12 psi)