KICKSTART YOUR RACING CAREER
The new KTM 125 SX is the most compact and lightweight of the full-size bikes and delivers a confidence-inspiring ride like no other. A new lightweight chassis teams up with the most competitive 125cc 2-stroke engine to date, delivering superior agility and power to fulfil the demands of any young adrenalin seeker. This 2-stroke screamer is the ultimate entry point into the pro ranks and a sure-fire way to add to the trophy collection.
ENGINE & EXHAUST
The latest version of the 125 SX engine is once again the most competitive and powerful engine in its class. With an outstanding power-to-weight ratio, low cost and overall simplicity, it is clear that 2-strokes will continue to have a successful future at KTM. The compact and durable 17.2 kg engine was developed using the latest KTM engineering know-how, resulting in broad power across the rev range. Its easy rideability and outstanding performance are benefits that equate to faster lap times and better results.
At the heart of the 125cc engine is a reworked cylinder with a 54 mm bore. It features an improved power valve unit with a sophisticated mechanism designed for the lateral support exhaust ports. The new exhaust port layout increases engine performance, while the upper contour of the exhaust port has been machined to ensure more accurate port timing. Together with the two-component cylinder head, the newly reworked cylinder is key to the KTM 125 SX's outstanding performance across the entire rev range.
CRANKCASES AND ENGINE COVERS
The lightweight engine cases are manufactured using a high pressure die-cast production process, keeping wall thickness to a minimum while retaining strength and durability. The design allows for a high crankshaft position which is located close to the center of gravity, resulting in optimal mass centralization and easier ride-ability. The engine body is extremely compact, which contributes significantly to the low engine weight. Additionally, for 2019, the seat of the kickstart intermediate gear has been reinforced for improved reliability and thanks to the new clutch arrangement, the clutch cover is lower, reducing the engine width by 10 mm.
The KTM 125 SX is now fitted with a new, more robust 6-speed transmission. The gear ratios were carried over from the predecessor, but all the gears feature improvements and reinforcements. Another highlight of the 125 SX transmission, is the no dirt gear shifter. Similar to the footpeg design, it prevents the build-up of dirt and ensures the next gear is always available, no matter what the conditions.
The KTM 125 SX is fitted with a MIKUNI TMX carburetor. The settings on the 38mm flat slide carburetor have been adapted to suit the new airbox, providing smooth, controllable power all the way through the rev range.
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.
When it comes to improved power delivery and performance, the new exhaust plays a key role and packs a punch that is hard to beat. In addition, its new shape provides slimmer ergonomics while still operating safely within the noise limits for racing.
To heighten the highly energized riding experience of a 125cc 2-stroke, KTM developed a new chassis that is light and responsive enough to enhance its dynamic reputation. For 2019, the KTM 125 SX features a new lightweight, high-tech steel frame that not only responds accurately to rider input, but has also been optimized for better rider feedback. The new flex characteristics help the bike to soak up those big hits while also delivering excellent agility and high-speed stability. As a whole, this new chassis allows the rider to be 100% in charge of the ride.
The all-new frame and subframe on the KTM 125 SX cater to the aggressive riding styles associated with 125cc racing. For this reason, as with the rest of the SX range, the frame is professionally crafted from hydro formed Chromium Molybdenum steel tubes that are robot welded, ensuring the highest levels of consistent quality. Improved stiffness has been precisely tailored for better handling, while working in harmony with the suspension, for agility without losing high-speed stability. The frame also features "no-dirt" footpegs, which have a simple but effective self-cleaning system which ensures the footpegs return to their original position, providing complete control in all conditions. For 2019, all SX frames feature the same highly durable powder coating as the KTM Factory machines and come with standard frame protectors. The new subframe is 40 mm longer and made from lightweight aluminum, for improved rear fender stability.
The new KTM 125 SX one-piece swingarm, is manufactured using a gravity die-cast production process, offering exceptional strength at the lowest possible weight. The reshaped axle slot provides an additional 5 mm of axle adjustment, which allows the wheel to be set further back, for improved straight-line stability on really rough tracks. The chain measurement markings on the swingarm are clearly visible from above, making chain adjustment simple and accurate.
KTM uses lightweight, CNC-machined hubs and high-end Excel rims on all SX models, guaranteeing maximum stability and minimum weight. For 2019, the aluminum spoke nipples feature a reworked design, which conveniently reduces the frequency with which the spokes need to be tightened. The wheels are fitted with the latest Dunlop Geomax MX 3S tires, delivering maximum grip and stability and effectively transferring all the power to the ground.
All full-size SX models are fitted with the super-lightweight WP AER 48 front fork. It is a 48 mm USD air-sprung fork with separate functions for each fork leg, meaning damping functions are on the right side and the air spring is on the left. The left leg features a two-chamber system with a capsuled air cartridge, helping prevent loss of air pressure. Essentially, this means that in the rare case of a leaking outer seal, the internal cartridge pressure keeps the bike in a normal position. The air spring is exceptionally easy to use and can be adjusted to any rider weight via a single air valve and the air pump that is supplied with the bike. The right fork leg integrates a damping cartridge to fit single damping leg requirements and can be adjusted to the track conditions and the rider's preferences. (compression from top, rebound from bottom, 30 clicks each). For 2019, new settings on the damping side have improved the damping characteristics, providing great front end feel and control.
All SX models feature a DDC monoshock, which has been developed to work as a complete unit with the entire frame and swingarm architecture, as well as the linkage system and the AER 48 forks. It features high-quality machined and anodized components, which add a touch of class and give it appeal beyond just a functional necessity. Internally, the shock houses an updated main piston and new settings that provide improved damping characteristics, perfectly complimenting to the reworked front-end setup. It is fully adjustable, including high and low speed compression, allowing you to set the shock up precisely to suit any track and rider's preferences.
All SX models feature top quality, CNC-machined triple clamps and have become somewhat of a KTM trademark. For 2019, the triple clamp has been reworked with stiffer upper clamps (22 mm offset for all models) to suit the reworked frame stiffness and flex characteristics of the latest WP AER forks. The result is a front end that works in perfect harmony with the frame, improving overall handling and stability. The rubber damped handlebar fixation reduces vibration and also allows for some adjustment with 2 different mounting positions. An hour meter is fitted as standard on the upper triple clamp on all SX models, keeping the rider informed the number of hours spent tearing up the track and when the next service is due.
High-tech Brembo brakes have always been standard equipment on all KTM motocross bikes. Combined with lightweight wave discs, the renowned system provides the highest level of braking efficiency, enabling you to always out-brake the competition.
All models in the SX range are fitted with newly designed lightweight polyethylene fuel tanks. The fuel capacity on the full-size SX models is still 7 liters, but the new shape improves the ergonomics. The filler cap has an inside thread that makes for easy and reliable closure.
The new airbox on the KTM 125 SX has been completely reworked to ensure better flow dynamics, resulting in optimal power and throttle response. Despite the obvious performance enhancements, the new design also offers maximum protection against soiling of the air filter. The large Twin-Air air filter is mounted on a cleverly designed stiff cage that minimizes incorrect installation. As found on previous models, filter maintenance is quick and easy and does not require tools - a standard, original feature from KTM.
ERGONOMICS & COMFORT
Momentum is crucial when laying down fast laps on a 125cc. The ability to shift your weight quickly and easily to work in perfect harmony with the motorcycle is key to maximizing flow. KTM has focused extensively on the optimal ergonomics for high-level performance, ensuring a riding position that offers the best control and, with the option of several handlebar positions, can be adjusted to suit every rider and condition. The way a rider interacts with the bodywork, seat, footpegs and handlebars, results in maximum balance and control. For this reason, no compromises were made in these important areas and only the best quality products and designs were used. Sitting on the 2019 KTM 125 SX gives the rider a definite sense of control and this is immediately confirmed the moment he hits the track.
All SX models have a newly shaped seat, designed to match the improved ergonomics. The seat cover features newly developed silicone strips that provide better feel and grip for the rider. The seat is conveniently fixed to the bike using one long, lateral screw, making it safe and easy to handle.
All full-size SX models are equipped with the same high-strength aluminum tapered handlebar, made by NEKEN. The handlebar is fixed in rubber damped mountings, which allow for two different positions. The handlebars come standard with an ODI vulcanized grip on the right side and a comfortable ODI lock-on grip, which does not require any wire or glue, on the left. They also feature a reworked bar-pad with a newly designed cover that can be attached and removed a lot quicker and easier. These handlebars offer a rider the control to attack the track in true aggressive 125cc style.
Sophisticated 'No Dirt' footpegs prevent smudging up the pegs, 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.
BODYWORK & GRAPHICS
125 cc riders are renowned for riding with the most aggressive body language. Young, determined athletes riding with exuberant style and pushing themselves and their machines to the limit. This critical consideration went into the development of the bodywork of the KTM 125 SX and was factored into the entire 2019 SX range. By using input from KTM factory riders, KTM R&D as well as Kiska Design, the new bodywork of the KTM 125 SX achieves complete harmony between rider and bike. The main goal was to provide the perfect contact points for the rider, allowing him to move as freely as his spirit demands, with the control to match his intentions. The bodywork is full of intelligent design elements, like the I-beam structure on the front and rear fenders, which guarantee maximum stability with the lowest possible weight. The new modern design and graphics portray an impressively fast and aggressive look that sends a clear message to the competition.
The 2019 SX models feature the latest in-mold graphics, matching the new bodywork perfectly. They have a fast and aggressive style that screams READY TO RACE, leaving no doubt as to the bikes' high-performance intentions.
SOFTWARE & ELECTRONICS
Absolute performance purity is the name of the game when it comes to electronics and the new KTM 125 SX. Undiluted 2-stroke simplicity, with an hour meter to keep a check on how long you've been shredding and an optional rev counter to assist with perfect setup.
1-cylinder, 2-stroke engine
Wet multi-disc clutch, hydraulically actuated
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
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.
All information concerning the scope of supply, appearance, services, dimensions and weights is non-binding and specified with the proviso that mistakes, printing, setting and typing errors may occur; such information is subject to change without notice.