VOL. 54 ISSUE 8 FEBRUARY 28, 2017 P77
(Top) The Yamaha's
five-speed
transmission is
tweaked to better
accommodate the
trails. However, the
Honda's tranny,
also a five-speed,
is unchanged from
its MX cousin.
(Bottom) Except
for the standard
electric starting, the
RX's engine is the
same as the R's.
ent on the FX to work in con-
junction with the electric starter.
The ECU is exclusive to
the YZ450FX and uses differ-
ent mapping to provide more
off-road friendly power. It can
still be heavily tuned using the
GYTR power tuner.
The transmission ratios are
30% different between the YZ450F
and the YZ450FX. To theoretically
match the YZ450F first gear to the
YZ450FX you would add 14 teeth to
the YZ450F's rear sprocket. Then
you would add eight teeth to match
second gear, two teeth to match third,
zero teeth to match fourth (fourth
gear nearly the same), and you then
subtract four teeth to match fifth gear
on the FX.
The YZ450FX suspension uses all
the same components as the YZ450F
and the chassis is identical as well.
The internals of the suspension are
where things are different for the
YZ450FX. Yamaha went down five
YAMAHA YZ450FX
Yamaha didn't simply bolt on
an 18-inch rear wheel and
called it a day. They went
further in the morphing pro-
cess from MXer to off-road-
er than KTM, which doesn't
change a lot between the
SX-Fs and the XC-Fs. The
YZ450FX engine is very similar to the
YZ450F, but comes to life via an elec-
tric start, requiring a left-side case
change to hold the starter and a more
powerful generator. Power output
went from 95 watts to 160 watts. For
2017 it no longer has a kick-starter as
backup.
To smooth out power Yamaha add-
ed flywheel inertia and the FX uses
a different crankshaft. One-hundred
percent of the reciprocating weight is
balanced by the counter-balancer; on
the YZ450F it's 88 percent.
The cylinder head and piston are
the same as the motocross version
and the cams are only slightly differ-
(Left) For such
big, heavy and
powerful bikes,
both the Honda
and Yamaha are
remarkably agile
and easy to ride
on technical
trails.
