KTM 250 SX-F 2018:SMALL-BORE SUPERSTAR
The KTM 250 SX-F has been on top of the MX2 World Championship for many years now and just added another world title to its crowded trophy cabinet. But that’s no surprise. The combination of a powerful and torquey engine in a lightweight and agile chassis is bound to place the KTM 250 SX-F onto podium after podium.
The KTM 250 SX-F engine is known to be the strongest
engine in the MX2 paddock. It screams at the top
of its lungs at 14,000rpm, but is equally happy producing
tons of torque and power across the rest of the
rev range. Its compact architecture contributes to an excellent
mass centralization, supporting the rideability of the bike.
And it only weighs 26.1kg. That’s including the incredibly
The centerpiece of the compact DOHC (double overhead camshaft)
engine is the cutting-edge cylinder head. It features two overhead
camshafts, which activate the titanium valves via super-light
cam followers with a hard DLC coating.
The KTM 250 SX-F’s crankshaft utilizes a short connecting
rod, which makes for an overall compact and lightweight
engine with a snappy power delivery. A plain big
(bottom) end bearing with two force-fitted bearing
shells runs directly on the crank pin. The necessary oil
feed for this bearing is ensured by the engine’s pressurized
lubrication. This design is a decisive benefit in terms of the
crankshaft service interval, which can be lengthened
due to the plain bearing. So just pin it, all day long.
The KTM 250 SX-F is fitted with a unique E-starter as standard,
which is a clear advantage when it comes to crunch time
in the heat of battle. A strong starter motor made by
Mitsuba will fire time and time again at the push of
a button. Even under extreme conditions, thanks
to its more heat resistant O-ring.
This reliable piece of engineering has been skillfully balanced
to guarantee minimal vibrations. In its latest form, it
allows a decrease of the displacement to 125cc just by
replacing cylinder, piston and head. There’s no more
need to change the crankshaft. Two-in-one in no time.
CRANKCASES AND ENGINE COVERS
The design of the die-cast crankcases allows for minimal
weight and a very centralized shaft configuration. This
makes the engine short and compact, while contributing
to an efficient centralization of masses. The engine covers
also feature a solid surface structure, which reduces
the wear caused by the rider’s boots. This way,
your SX-F will keep looking better longer.
The reliable 5-speed transmission features a special
surface treatment on the 2nd, 3rd and 4th gears
for solid reliability. The advanced ´No Dirt´ gear shift lever
design prevents dirt from jamming the joint of the lever and
guarantees precise shifting even in the muddiest conditions.
All 4-stroke SX-F engines are fitted with a gear position sensor
for tailored engine mapping for each gear. In MY18, the
transmission shaft gets a new C4 bearing that has a bigger
overlap in the case. This means reliability even under
extremely hard conditions. Think GP-level riding.
In knee-deep sand.
CYLINDER AND PISTON
Inside the short cylinder, with a bore of 78mm, thumps a
box-type piston made by CP. Its crown geometry
is adapted perfectly to the high-compression combustion
chamber (14:1), where its rigid structure and low
weight shine. Thanks to the low oscillating masses,
the engine is as cheerful as it’s strong.
ENGINE MANAGEMENT SYSTEM
The state-of-the-art Keihin Engine Management System
with electronic fuel injection features a 44mm throttle body.
Thanks to its unique injector position, the engine’s response
is instantaneous. And to make life even easier, separate
systems for cold starts and idle adjustment await you. The
lightweight ECU features a unique traction and launch control
system for lightning-quick response when the bar drops and
maximized grip thanks to different maps that sync with
to the gear you’re in. As an ultimate bonus, the rider
can unleash an even more powerful mapping via
the handlebar map switch.
The KTM 250 SX-F employs the KTM-developed CSS
clutch (coil spring steel) with a robust steel basket and
extremely heat resistant clutch plates and new, nitrated steel
liners reducing the wear. Light operation and telepathic amounts
of control are standard with this hydraulic Brembo
The side-mounted balancer shaft does double duty also
driving the water pump. Thanks to its perfect balance and
low oscillating masses, engine vibration is kept to a minimum.
KTM’s proven cooling system routes the coolant from
the cylinder head through the frame triangle, directly
to aluminum radiators made by WP. Thanks to flow optimized
internal circulation and CFD-calculated ventilation, the system is
superbly efficient. In addition, new radiator protections improve
heat dissipation. Especially in the mud. They are also integrated
into the front part of the shrouds to protect the
radiators in a crash.
The main target for the KTM engineers when developing the
SX models was a massive weight reduction compared to
the previous generation. The result: the current SX-F
models are the slimmest, lightest bikes in the competition,
even though the 4-strokes are equipped with an electric
starter as a standard feature, while the competition
still needs to be kick started. You can just focus on
Sophisticated ´No Dirt´ footpegs prevent clogging of the
footpeg pivot, even when digging in deep ruts. Looking
for a higher riding position? Then just mount the footpegs
of the MY2018 EXC models, which are 6mm higher
than the SX versions
FIM noise limits are a real challenge for every manufacturer.
Therefore, KTM has put a lot of effort into the development
of their exhaust systems. All 4-strokes are fitted with headers
that have a unique standard feature; an additional resonator
system – a small chamber connected to the pipe. All 4-strokes
are fitted with a short silencer, mounted as close to the
engine as possible. You know what that means: extra mass
centralization and better rideability. Its advanced internal design
reduces the noise sufficiently in order to sit safely
below the noise limit, while still raising the hairs on your neck.
The high-tech, lightweight chrome-moly steel frame has a
knack for easy handling, outlandish rideability, precise cornering
and excellent stability. You can also count on high torsional
rigidity and low longitudinal stiffness. This results in better
absorption of the energy created from the front and rear
suspension, sucking up jumps and bumps. In short: more comfort
and less rider fatigue. Laterally attached, lightweight aluminum
engine head stays (the connection between cylinder head
and frame) contribute to more precise cornering and a
reduced vibration level. The engineers were able to pull
off all that, while making their frame a big fat kilogram
lighter than that of the lightest competitor on the market.
In addition, it is easier to maintain, easier to work on and
supplies more space for the tank and other components.
The bike also features an extra-light subframe made
of stable aluminum profiles, which tiptoes the scales
at less than 900g.
AIR FILTER BOX
The airbox design offers maximum protection of the air filter
against soiling, while ensuring maximum airflow. The large
twin-air filter is mounted in a stiff cage, which at the same
time holds the system in place. This design is so simple,
you could still pop a fresh one in with a face full of mud. Without
tools. In seconds.
The cast aluminum design offers low weight and a perfect
flex behavior. The single-component casting process
eliminates any inconsistencies and inherent weak points
created by welding. It’s better looking too.
KTM engineers sure know how to handle handlebars. This
tapered one, made of high-strength aluminum, is fixed
in damped rubber mounts and has two different positions.
ODI lock-on grips make grip changes easy and
do not require any wire or glue to be secured.
A lightweight polyethylene tank with a capacity of 7.0 liters
of juice. The filler cap has an inside thread, which
makes for easy and reliable closure.
The KTM wheels feature lightweight, CNC machined
hubs and high-end Excel rims guaranteeing maximum
stability at minimum weight. The wheels are
fitted with the latest Dunlop Geomax MX 3S tires.
The WP shock absorber has been developed with the entire
frame and swingarm architecture in mind, including the
linkage and the WP AER 48 front fork. It features machined
and black anodized components and is a valuable, high-end
product compared to roughcast reservoirs. A new,
confidence inspiring setting with improved damping characteristics
perfectly matches the front-end setup and its sparkling
WP color scheme lets everyone know you have
excellent taste in suspension.
The lightweight WP AER 48 front fork, a 48mm USD air-sprung
fork developed by WP in close collaboration with KTM, is a
split fork with separate functions for each leg. That means
damping functions are on the right side, whereas the air
spring is in the left. This left leg features a 2-chamber system
with a capsuled air cartridge to prevent loss of air pressure.
Should the outer seal start to leak, the internal cartridge
pressure will keep the bike in position. The air spring is easy
to adjust to any rider weight via a single air valve. No special
tools are required; the air pump supplied with the bike will do
just fine. The right fork leg integrates a damping cartridge
that tailors to all your damping needs. It can be adjusted to
the track conditions and the rider’s preferences with a twist of
a dial (compression from the top, rebound from the bottom,
30 clicks each). Right off the dealer floor, this fork (with reworked
damping characteristics) is more comfortable and more
sensitive than ever. But you can still hammer the hell out of it.
Top quality, CNC machined triple clamps have been a KTM
trademark for years to ensure precise handling. The rubber
damped handlebar fixation allows for two positions and
an hourmeter is fitted in order to let the rider know it’s
time for a service.
These high-tech Brembo babies are combined with
lightweight Wave brake discs. You couldn’t brake
any harder, better, faster or stronger.
HANDLEBAR MAP SELECT SWITCH
All 4-stroke models are equipped with a multi-functional
handlebar map select switch, which does three things:
Activation of the traction control Activation of
the launch control Selection of an alternative power
curve (Standard or Advanced) The traction control is a
unique feature that none of the competitors can offer. It
guarantees more efficient traction when the track conditions
are less than perfect. Push the tip switch and reign supreme.
With this map select switch the rider can also activate the
launch control, which provides more efficient starts out of the
gate so you can go for the holeshot, time and time again.
How? It simply reduces the maximum engine speed for the
very first moment of the start, in order to give you better
control. Push both tip switches when the engine idles and the
EFI control lamp mounted on the upper triple clamp will let you
know you are READY TO RACE. In addition, the map select
switch gives the rider the chance to select an alternative,
more powerful map beside the standard configuration.
Welcome to the future.
BATTERY & WIRING HARNESS
A strong new lithium ion battery breathes life into the engine
and contributes to low vehicle weight. The lightweight
battery and wiring harness are centralized in a compartment
above the air filter box, allowing the mechanic to
remove the subframe without getting in conflict
with the electronics. A happy mechanic is a good mechanic.
Like all KTM 4-stroke motorcycles, the 250 SX-F is started at
the push of a button - a priceless advantage when you’re on the clock.
KTM R&D, KISKA Design and all our factory riders had their
say in shaping the plastics with one goal: complete harmony
between rider and bike. Perfect ergonomics and contact points
provide maximum comfort in movement on the SX-F. The I-beam
structures of the front and rear fenders guarantee maximum
stability and a low weight thanks to well thought-out
construction and mounting. They also stay cleaner for longer.
A new, tailor-made kit and a Factory orange frame. Because
in this sport, champs deserve to look the part regardless of the dirt.
|Design||1-cylinder, 4-stroke engine|
Secondary gear ratio
|Clutch||Wet, CSS multi-disc clutch, Brembo hydraulics|
|25CrMo4 steel central-tube frame|
WP-USD, AER 48, Ø 48 mm
WP shock absorber with linkage
Suspension travel (front)
Suspension travel (rear)
Front brake disc diameter
Rear brake disc diameter
5/8 x 1/4"
Steering head angle
1485 ± 10 mm
Tank capacity (approx.)
Weight READY TO RACE (without fuel)