KTM 125 SX 2018:KICKSTART YOUR RACING CAREER
The whip cracking KTM 125 SX has been at the front for years. With phenomenal performance on tap, it will be there for many more seasons to come. A compact chassis and the lowest weight out there is teamed up with a high performance 125cc 2-stroke engine for a surefire trophy collection. Get shredding, youngsters.
The latest KTM 125 SX engine is the most powerful and most
competitive engine in its class; a clear statement that
KTM is keen on keeping 2-stroke technology at the
forefront of development. The secret to their success is
an outstanding power-to-weight ratio, low costs and simplicity.
This 125cc ripper has been developed with the latest KTM
engineering know-how and the most advanced technology
available. The results: class-leading power across
the rev range, while being extremely compact and
ultra-light at a mere 17.2kg. Our work here is done;
now it’s up to you to collect the trophies.
This compact cylinder with a 54mm bore features a
cutting-edge power valve unit with a sophisticated
mechanism for the lateral support exhaust ports.
Matched to a twin-component cylinder head, it is
KTM’s secret to all-round grunt. The layout of the water
jackets in the cylinder and head guarantees efficient
heat dissipation when the going gets tough.
The KTM engineers designed lightweight die-cast
crankcases featuring a high crankshaft position located
close to the center of gravity, which results in optimal
mass centralization and outstanding rideability.
The KTM 125 SX is fitted with a MIKUNI TMX carburetor.
This 38mm flat slide carb lives to provide smooth and controllable
power all the way up to the rev limitation. With a new intake
manifold the carburetor is turned 7° in order to reduce the
overflow of fuel. And it’s less sensitive to different
altitudes and temperatures, so you can pin it
This reliable piece of engineering has been skillfully
balanced to guarantee minimal vibration. In its latest
form, it allows an increase of the displacement to 144cc
just by replacing cylinder, piston and head. There’s no
more need to change the crankshaft. Two-in-one in no time
A robust 6-speed transmission was designed specifically
for the small 2-stroke engine, its gear ratios perfectly
in sync with the 125’s power band. A reworked 3rd, 4th
and 5th gear further improve reliability. The latest
production technologies allowed for compact dimensions
and minimal weight. Keeping safety in mind,
an advanced ´No Dirt´ gear shift lever design prevents
dirt from blocking the joint.
The engineers meticulously tuned the resonator
chamber for maximum torque and power, so this
little screamer is as tough as it is strong.
All 2-stroke models feature a new CDI control unit with an
advanced hardware which improves the starting behavior
of the engine. The ignition curves remain unchanged.
KTM engineers just love dropping weight year after year.
The result: the 2018 KTM SX models are the
slimmest, lightest dirt bikes out there.
AIR FILTER BOX
The air filter box 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 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, engine head stays (the connection between
cylinder head and frame) are now made of lightweight
aluminum. They 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.
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 MY18 KTM EXC models, which are
6mm higher than the SX versions.
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.
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.
Featuring lightweight, CNC machined hubs and high-end
Excel rims, they guarantee maximum stability and
minimal unsprung weight. The wheels are shod
with the latest Dunlop Geomax MX 3S tires.
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.
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. 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.
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 fork 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.
|Design||1-cylinder, 2-stroke engine|
Secondary gear ratio
|Clutch||wet 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)