TransWorld Motocross — September 2017

084 OFF-TRACK BY THE TESTING STAFF OF TWMX

2017 YAMAHA YZ450FX

What differentiates an off-road or trail motorcycle from a motocross machine? In the past, the vari-
ances were mostly the accessories a rider finished the bike with, be it a set of handguards, a flywheel
weight, or a spark arrestor. In recent years, however, manufacturers have added race-ready woods and
desert models to their products lines, and Yamaha is one such brand. With the racy YZ450F bike as its
base, the company has retooled the engine and chassis for a bike that is better suited for the trails than
it is for motocross and released the YZ450FX.
What do we mean when we say that Yamaha used the YZ450F as the base for the YZ450FX? They are
built around the same bilateral beam aluminum frame, a design that Yamaha has worked with for years and
centers the weight of the engine, fuel tank, and exhaust into one condensed area. The general configura-
tion of the dual overhead cam engines remains the same, as both are powered by a 44 mm Keihin throttle
body fuel injection system, which feeds into the rearward slanted cylinder that allows for a direct flow from
intake to the wraparound exhaust. And lastly, both ends of the bike are supported by Kayaba suspension
components with SSS mechanical spring forks on the front and a traditional shock on the rear.

Despite the similarities, numer-

ous tweaks have been made to

better prepare the bike for off-road

riding. A battery-powered electric

starter fires up the engine, and this

resulted in a design change for the

left-side case. The power

output has been refined

with cams, crankshaft,

ECU, and flywheel that

are specifically for the FX

machine, while the clutch

and gear ratios of the

five-speed transmission

have been transformed

to better work through

tight terrain. Since there

are far fewer and smaller

jumps off-road than there

are on a track, the spring

rate of the FX fork is

lighter and both ends of

the suspension have off-

road motivated valving. The final

changes to the FX are the 18-inch

rear wheel, Dunlop AT81 tires, side

stand, O-ring chain, and plastic skid

plate that come as regular equip-

ment. Two lights are located near

the handlebars and give warnings

should the fuel or oil levels drop.

These changes bring the claimed

wet weight of the FX to 262 pounds,

a 15-pound increase over the moto-

cross model.

The fit and finish of the YZ450FX

are standard Yamaha, with adjust-

able bar mounts, high-quality brakes

(the 270 mm front and 245 mm rear

rotors are the same on both the

YZ450F and YZ450FX), embedded

graphics, and two-gallon fuel tank.

ON THE TRAIL

With so many similarities between

the two bikes, it’s no surprise that

the cockpit of the YZ450FX feels

familiar. The seat, pegs, handlebars,

levers, and grips are all the same,

yet a reach for the kickstart lever

comes up empty. For 2017 the inter-

nal mechanisms for the manual sys-

tem have been completely removed

in an effort to save weight, but the

small yet powerful battery pack

and starter are up for the task. We

applaud this decision by Yamaha

because there are few things worse

than attempting to re-fire a hot four-

stroke after a lengthy ride.

“THERE’S NO

DENYING THAT THE

YZ450FX IS AT ITS

CORE A YZ450F,

THE BIKE THAT

CLAIMED 450 BIKE

OF THE YEAR

HONORS IN OUR

2017 SHOOTOUT.”

On the trail, we immediately no-

ticed how much different the engine

performed compared to our moto-

cross machine, mostly due the wide

gear ratios. The first few gears in the

five-speed transmission are okay for

low speeds or technical, tight sec-

tions, while the latter gears are great

for high speeds. It takes an active left

hand to make the most of the rather

short first and second gears, some-

thing that the smooth clutch is more

than capable of handling. Even with

the off-road designed crank, ECU,

flywheel, and cams, there’s no de-

nying the muscle of the 450cc pow-

erplant. Simply put, the engine is at

its best in wide-open areas because

there is no stumble in performance

from the middle to top of the rpm

and gear range. It’s worth noting

that the bike’s stock exhaust system

does not come with a spark arrestor.

The handling of the YZ450FX is

much like the YZ450F. Although the

off-road bike is heavier than the mo-

tocross bike, the added girth is felt

in only a few instances, like when

hard on the brakes or in a slow,

obstacle-filled area. Even with all of

this, the bike is still agile enough to

cut through the woods and stable

enough to make high-speed runs

over fast sections. The 18-inch rear

wheel changes things like the over-

all wheelbase and ground clearance

by a small amount, but we had no

qualms with its use, as it’s often the

first swap that off-road riders make

on a new bike.

We’ve praised Kayaba’s SSS fork

and matched shock across the YZ-

YZF line, and that continues with the

YZ450FX. The traditional design of

the mechanical spring fork is easy

to understand and maintain, and it

performs exactly as one would hope

all the way through the stroke. Since

off-road areas are littered with small

obstacles like rocks, roots, ruts, and

small jumps, the spring rate and valv-

ing on both ends of the suspension

are understandably softer than what

comes on a motocross machine. The

stock settings on the YZ450FX are