EasyManuals Logo

Yamaha YZ250 2021 User Manual

Yamaha YZ250 2021
148 pages
To Next Page IconTo Next Page
To Next Page IconTo Next Page
To Previous Page IconTo Previous Page
To Previous Page IconTo Previous Page
Page #138 background imageLoading...
Page #138 background image
CHASSIS
8-9
EAM20119
CHASSIS
EAM30168
SELECTION OF THE SECONDARY
REDUCTION RATIO (SPROCKET)
<Requirement for selection of secondary gear
reduction ratio>
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, howev-
er, as the speed depends on the ground condi-
tion of the day of the race, be sure to run
through the circuit to set the machine suitable
for the entire course.
In actuality, it is very difficult to achieve settings
suitable for the entire course and some set-
tings 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 secondary reduc-
tion 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.
EAM30169
DRIVE AND REAR WHEEL SPROCKETS
SETTING PARTS
EAM30170
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 surface.
Under a stony or a hard road condition, the tire
Secondary reduction ratio = Number of
rear wheel sprocket teeth/Number of
drive sprocket teeth
Secondary reduction ratio
3.571 (50/14)
Part name Type Part number
Drive
sprocket “1”
13T 9383E-13216
(STD) 14T 9383E-14215
Rear wheel
sprocket “2”
47T 17D-25447-50
48T 17D-25448-50
49T 17D-25449-50
(STD) 50T 17D-25450-50
51T 17D-25451-50
52T 17D-25452-50
Standard tire pressure
100 kPa (1.00 kgf/cm², 15 psi)
Extent of adjustment
60–80 kPa (0.60–0.80 kgf/cm², 9–
12 psi)

Table of Contents

Questions and Answers:

Question and Answer IconNeed help?

Do you have a question about the Yamaha YZ250 2021 and is the answer not in the manual?

Yamaha YZ250 2021 Specifications

General IconGeneral
Engine Type249cc liquid-cooled 2-stroke; reed-valve inducted
Bore x Stroke66.4mm x 72.0mm
Compression Ratio8.9~10.6:1
IgnitionCDI
Transmission5-speed; multiplate wet clutch
Final DriveChain
Suspension RearKYB® single shock; fully adjustable, 12.4-in travel
Brakes FrontHydraulic disc, 270mm
Tires Front80/100-21
Tires Rear110/90-19
Width32.5 in
Height50.8 in
Wheelbase58.5 in
Ground Clearance14.2 in
Fuel Capacity2.1 gal
Wet Weight227 lb
Fuel DeliveryKeihin PWK38S carburetor
Suspension FrontKYB® Speed-Sensitive System inverted fork; fully adjustable, 11.8-in travel
Brakes RearHydraulic disc, 245mm

Related product manuals