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.
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 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 wherever, whenever.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1-cylinder, 2-stroke engine
Secondary gear ratio
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)
The illustrated vehicles may vary in selected details from the production models and some illustrations feature optional equipment available at additional cost.
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