2010 Kawasaki KX450F
Already ranked at the top of its class
in numerous enthusiast magazine shootouts, for 2010
receives a number of engine and chassis updates to
ensure its winning potential.
The KX450F base package provides an
excellent platform for experienced racers to win races
in the top
classes. Design of the highly rigid aluminium frame,
suspension components and settings focused on
delivering superb high-speed stability – especially
in straight lines – to enable race-experienced
riders to ride
full out. And to deliver holeshot-winning performance
– a key factor that can mean the difference
between running up front and winning, or getting stuck
mid-pack – chassis geometry and the hard-hitting
4-stroke engine’s wide powerband were designed
to maximise rear wheel traction. The combination is
a proven race-winner, with Kawasaki racers regular
To keep the Lime Green racers out in
front, Kawasaki engineers made a number performance-enhancing
updates to both engine and chassis. Feedback from
factory racers resulted in a number of refinements
that deliver increased high-rpm and over-rev performance.
The new engine has specs on par with Ryan Villopoto’s
KX450F racer. Also inherited from the racing world,
a new piston with bridged-box bottom makes its first
appearance in a mass-production machine. Finally,
fine-tuning of the clutch results in improved
Chassis updates focus on making the
KX450F even easier to ride fast. Revisions to the
frame and uspension components result in lighter handling,
improved suspension action, increased comfort and
greater cushioning when landing jumps. Already acclaimed
as the best looking motocrosser in the paddock, the
KX450F once again sports sharp factory-racer looks
that are more than skin deep. Sleek, functional bodywork
was designed to offer racers a slim rider interface
to further facilitate going faster.
The KX450F – designed to give
racers the competitive edge to run out front.
Fuel-injected 449 cm3 liquid-cooled,
4-stroke Single delivers hard-hitting power from low-
through high-rpm. The broad powerband and responsive
throttle offer a broad spread of torquey response
that enables racers to get on the gas and go even
from down low. In addition to the inherent benefits,
fuel injection contributes to the KX450F’s lag-free
acceleration, especially after landing jumps. For
2010, a number of refinements, including the first
mass-production use of a high-performance piston featuring
a bridged-box bottom, offer improved performance in
high-rpm and over-rev ranges, and modifications to
deliver improved clutch feeling.
New piston, featuring the same design
used on our factory racers, offers improved performance
at all rpm.
A revised profile with a shorter skirt, reinforced
external ribs and the first mass-production use of
a bridged-box bottom, featuring fully flush internal
bracing, results in a lighter, stronger piston.
Shorter piston pin has a smaller inner
diameter for increased strength.
Intake camshaft with revised sprocket/shaft
arrangement moves intake valve timing 2o forward,
to suit revised engine characteristics.
Crankshaft with a slightly higher inertial
mass (47.2 kg-cm2 >> 48.2 cm2) offers increased
performance. The balance factor is unchanged. Wedge-shaped
crank web increases offsetting moment
for high crankshaft balance factor. At close to 60%,
the balance factor of the ’10 KX450F is on par
with Ryan Villopoto’s factory racer. The result
is reduced engine vibration, smoother power delivery
and increased performance – especially at low
rpm, where response is noticeably snappier.
Refined power delivery
In addition to generating the electrical
output necessary to ensure easy starting, the large-diameter
ACG also contributes to engine feeling at partial
One-piece stainless steel exhaust pipe
is 40 mm shorter, contributing to improved mid-high
range performance. The optimised pipe line contributes
to improved ergonomics, and the new steel construction
offers enhanced durability.
On European models, revised internal
construction results in a silencer approximately 330
g lighter (on par with that of other markets). Material
trimmed from the spring holders and outer surface
of the operating plate optimise rigidity and improve
oil drainage from the clutch, contributing to more
Friction plates feature approximately
75% more friction material, contributing to a more
direct feel (particularly beneficial for hooking up
after landing jumps).
Operating plate pusher with increased
outer diameter reduces clearance between the pusher
and the hole of the input shaft, improving clutch
The following clutch revisions offer
more direct feel and increased control. Improved clutch
Designed specifically for motocrossers the fuel injection
system incorporates a small lightweight ECU and operates
without a battery to further eliminate unnecessary
weight. And of course, fuel injection eliminates the
need to adjust engine settings to suit track and climate
Ensuring quick starting without a battery
was a prime directive when developing the KX450F’s
fuel injection system. Using only electricity generated
by the kick starter, the engine can be started with
only three rotations of the crankshaft. The system
delivers electricity in the following order: 1) ECU,
2) fuel pump, 3) injector. With a warm engine, starting
can be accomplished in a single kick.
The compact, lightweight ECU, located
just in front of the steering head (behind the number
plate), was designed specifically for motocross use.
To help cope with the shocks and vibrations of motocross
riding, the fuel pump relay is built in to the ECU.
An optional KX FI Calibration Kit (containing
KX Racing software, an ECU controller, mounting bracket
and damper, harness and USB cable) allows racers to
adjust engine characteristics (by rewriting actual
data maps) to suit their preference. (In addition
to the kit, a PC and 12 V battery are all that is
required.) Please refer to the Appendix for more details.
The 43 mm throttle body makes use of
a progressive throttle link to deliver airflow in
much the same way as would a FCR carburettor. Using
two linked shafts, the throttle body opens more quickly
after the 3/8 open position, delivering sharp response
and excellent power feeling.
Ultra-fine atomising injector with
12 holes sprays particles with a droplet size of 60µ
for smooth power deliver and improved engine at partial
throttle. The injector was set at 45o, the optimum
angle for improved mid-range power. Lightweight flat-bottom
aluminium fuel pump is located in the plastic fuel
To ensure a stable fuel supply during
vigorous motocross riding the fuel pump features a
rubber fuel filter cover that wraps around the inlet
port and acts as a fuel trap. A fuel return hose from
the pressure regulator ensures there is always fuel
in the fuel trap.
New ECU operating programme and revised
setting data offer improved response at low-mid rpm.
Battery-less fuel injection system
The engine was tuned such that the
torque curve follows the limit of running resistance
for as long as possible. (Unchecked, engine torque
can exceed this limit, resulting in wheel spin, which
does nothing to help
Efforts were made to achieve the widest
possible torque band, so that traction efficiency
would be maximised for a greater part of the rev range.
The engine is almost upright (forward
lean angle is 3o) to help place the bike’s centre
of gravity in the ideal position for maximum traction.
Asymmetrical high-acceleration cams
yield high intake efficiency.
During the cylinder head casting process,
the cores for the intake ports were given a special
coating to make the intake ports smoother. The extremely
smooth surfaces that result increase intake efficiency
at all rpm.
Lightweight titanium valves (IN: 36
mm; EX: 31 mm) reduce reciprocating weight and offer
Aluminium valve spring retainers reduce
reciprocating weight for reliable valve control at
Double valve springs also help ensure
stable valve operation and allow a short cylinder
Cylinder skirt was strengthened to
match the increased engine performance.
New thicker (22 mm >> 32 mm),
wider (120.2 mm >> 127.8 mm) radiators with
increased fin and tube pitch are stronger, offer better
resistance to mud build-up, and maintain cooling performance.
Because the new radiators are stronger, reinforcing
brackets could be eliminated, resulting in lower overall
The screw-type adjuster on the cam chain tensioner
is equipped with a pressure spring. Because the system
automatically minimises the vibration caused by a
loose cam chain, it greatly reduces the chance of
a mishap during a race. (Non-automatic systems that
are tuned incorrectly can actually adversely affect
valve timing by putting too much pressure on the cam
The combination of the smooth-shifting,
close-ratio 5-speed transmission with the KX450F’s
low-rpm engine performance offers the rider the option
to shift to a higher gear when traversing rough sections.
Since this reduces the effect of sudden (unwanted)
throttle input, allowing focus to be given to racing
rather than careful throttle control.
In the event of a stalled engine during
a race, getting it started again as soon as possible
is a racer’s first priority, so the KX450F is
equipped with an automatic compression release (ACR)
system. The dual-weight centrifugal decompression
system fitted to the exhaust cam eases starting in
much the same way as a conventional lever-type system.
Sprocket-style chain drive roller helps
smooth engine braking by reducing the effect of driveline
lash when the rider gets off the gas quickly and play
in the lower side of the chain suddenly tightens.
The additional control facilitates corner entry.
The KX450F’s slim aluminium perimeter
frame is a lightweight construction composed of forged,
extruded and cast parts. Chassis balance and settings
were all set to suit race-experienced riders. The
centre of gravity and key dimensions (swingarm pivot,
output sprocket and rear axle locations) were chosen
so that the rear tyre would drive the bike forward
(instead of causing it to squat). For ’10 revisions
to the frame and
suspension components were designed to offer lighter
handling, improved suspension action, increased comfort
and greater cushioning when landing jumps.
While the frame remains essentially
the same as that of the 09MY model, a revised steering
stem shaft and new swingarm offer improved handling.New
steering stem shaft with lower rigidity contributes
to lighter handling. Swingarm with revised cross-section
also contributes to lighter handling. The alloy swingarm
uses a cast front section, tapered hydroformed spars
and forged chain adjusters.
- The New Uni-Trak rear suspension system mounts
the suspension arm below the swingarm, allowing
a longer rear suspension stroke. The longer stroke
in turn allows more precise rear suspension tuning.
- Revised linkage ratios for the New Uni-Trak rear
suspension further increase rear traction performance.
- Extensive rider testing was conducted to determine
the ideal linkage ratios and rear shock absorber
damping settings to achieve maximum rear wheel traction.
Superior rear wheel traction
- Kayaba AOS (Air-Oil-Separate) fork keeps oil
and air in 9 10 separate chambers for stable damping
performance during long motos. Low-friction fork
seals contribute to smooth action.
- Revised spring rate, revised damping settings
and the less rigid steering stem offer improved
action (especially at the initial part of the stroke)
and increased comfort.
- A super-hard DLC coating (Diamond-Like Carbon)
on the outer surface of the inner fork tubes reduces
sliding friction (and stiction) and gives better
action, contributing to the smoother ride. The coating
is even effective when the fork is exposed to lateral
forces that would usually hamper slide action, such
as during cornering. The increased surface hardness
also minimises scratches and damage to the tubes.
- Friction-reducing Kashima Coat on the inside of
the fork outer tubes contributes to smoother suspension
action (especially at the initial part of the stroke)
and a better ride feel.
- Revised shock spring rate and damping settings
contribute to increased stability and offer improved
cushioning when landing jumps.
- The rear shock features dual compression adjustability,
allowing high-speed and low-speed damping to be
- The rear shock also features the Kashima Coat
on the tank cylinder. The reduced friction smoothes
- The KX450F features petal brake discs front and
rear. In addition to helping reduce unsprung weight,
the wave shapes of the petal discs help clean the
brake pads for more efficient braking performance.
- Revised rear brake pad material offers stronger
- Rear caliper guard protects the caliper from
- A factory-style Renthal (standard-type) aluminium
handlebar is standard equipment.
- Rib-less rear hub and butted spokes reduced unsprung
- Rims are coated in black alumite – just
like our factory racers.
- Factory-style graphics complement the KX450F’s
highly tuned performance.
Factory-style and other race-oriented components
Designed with rider ergonomics in mind,
bodywork components offer the rider a slim interface,
the natural position making it even easier for racers
to go fast.
Formed using a double-injection moulding
process, 2-tone shrouds contribute to the slim package.
Fine-tuned to accommodate the new radiators, the shrouds
feature a slightly slimmer design. 2-tone side covers
are also formed using a double-injection moulding
process. Like the shrouds they contribute to the slim
package. A hole in the right-side cover helps cool
The frame widens at the ankles to offer
the rider better grip and narrows near the bend below
the seat to allow a slim riding position. The optimised
pipe line of the exhaust contributes to improved ergonomics.
Slim seat features firmer urethane which keeps its
original shape longer. The seat uses a slip-resistant
top surface for good grip when seated and smooth sides
for excellent rider mobility.
Wide (front-to-rear) footpegs designed
to offer grip and superb feel at the pegs. The clutch
cable boot features a large quick adjuster, making
it easier for riders to adjust play in the clutch
cable. Throttle grip has a unitised collar. The one-piece
unit provides additional stability during throttle
Lightweight short-length grips feature
a pattern designed to provide excellent grip.
- Fast-idle knob on the throttle body allows riders
to increase engine speed when first starting a cold
- The crankshaft and connecting rod received a
carburising and quenching treatment for additional
- The camshaft lobes and tappet surfaces feature
a soft-nitriding surface treatment for long wear
and high-rpm reliability.
- A large flap inside the air cleaner case helps
prevent the ingress of mud.
- The silencer uses long-fibre packing which is
much more resistant to being blown out of the tail
pipe than standard length packing. As a result,
packing needs to be replaced half as often.
- Rubber damper collar used for the rear silencer
mount also contributes to increased durability.
- Right-side crankcase is reinforced at the lower
engine mount for increased strength and durability.
- Designed to accommodate the in-tank fuel pump,
the plastic fuel tank is formed using a rotational
moulding (or rotomoulding) process that reduces
- Large synthetic skid plate offers great protection
with minimum weight.
- Revised front fender is thicker and more rigid.
- New chain with thinner inner links offers 20
g in weight savings.
- All markets now feature Bridgestone tyres (F:
M403; R: M404).