Yamaha YZ250 Owner's Service Manual page 564

SETTING
EC720000
CHASSIS
EC71P002
Selection of the secondary reduction ratio
(Sprocket)
Secondary
Number of driven sprocket teeth
reduction =
Number of drive sprocket teeth
ratio
Standard secondary
reduction ratio
*For EUROPE and CDN
<Requirement for selection of secondary gear
reduction ratio>
9 It is generally said that the secondary gear ratio
should be reduced for a longer straight portion
of a speed course and should be increased for
a course with many corners. Actually, 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 machine suitable for the
entire course.
9 In actuality, it is very difficult to achieve settings
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 mak-
ing notes of lap times to find the best balance;
then, determine the secondary reduction ratio.
9 If a course has a long straight portion where a
machine can run at maximum speed, the
machine is generally set such that it can devel-
op its maximum revolutions toward the end of
the straight line, with care taken to avoid the
engine over-revving.
NOTE:
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.
7-13
TUN
50/14 (3.571)
*49/14 (3.500)