The KTM 250SX-F has dominated the MX2 class world championship for several years and has just added a new world champion title to its impressive track record. Who could steal the show from him? Successful marriage between a powerful and torquey engine and a light and manoeuvrable chassis, the KTM 250 SX-F flies from podium to podium.
The engine of the KTM 250 SX-F is considered one of the most powerful in the paddock of the MX2 class. Able to reach without flinching the 14000tr / m and with a phenomenal torque well present over the entire rev range, this engine is responsive. Its compact architecture allows better mass centralization and exceptional road holding. Remember in passing that it weighs only 26.1kg, including electric starter.
The centerpiece of the compact DOHC engine, the new avant-garde cylinder head features two overhead camshafts responsible for actuating the titanium valves using ultra-light rockers coated with a DLC coating.
The crankshaft of the KTM 250 SX-F uses a shortened connecting rod. More compact and lighter, the engine also gains in nervousness. The crankshaft has a big end bearing and two bearing shells force-fitted directly into the crankpin. The oil supply to this bearing is provided by the engine’s pressurized lubrication circuit. This type of design, together with the big end bearing, contributes significantly to extending the crankshaft service interval..
To enhance the reliability of the 5-speed gearbox, the surface of the gears has received a special treatment for the 2nd, 3rd and 4th gears. The “zero dirt” design of the selector avoids the clogging and blocking of the lever articulation and guarantees ultra-precise gear changes even on the most muddy terrain. All SX-F 4-stroke engines are fitted with an engaged gear sensor that allows engine characteristics to be matched to each speed. On the AM18, the gearbox shaft has a new C4 bearing with greater radial play. This increases reliability, even under very demanding operating conditions. Something to get out of the sand in the middle of a Grand Prix.
The KTM 250 SX-F is fitted with an electric starter as standard, which is a decisive advantage in reducing lap times in competition. Activated by a simple button, this ultra-powerful electric starter manufactured by Mitsuba is not ready to let you down, especially since it now has an O-ring capable of withstanding extreme temperatures..
ENGINE CASINGS AND COVERS
The design of the molded crankcases has a double advantage: obtaining maximum weight reduction and allowing a very centralized shaft configuration in order to make the engine even more compact and to obtain a much more efficient distribution of masses. The new crankcase covers have a solid surface structure to reduce wear caused by the rider’s boots. The SX-F will thus be able to keep an eternal youthful air..
CYLINDER AND PISTON
The shortened cylinder, with a 78mm bore, accommodates a proven bridge-box piston, manufactured by CP. The geometry of the piston head, perfectly suited to the new high compression combustion chamber (14: 1), is characterized by a rigid structure and low weight. The reduced oscillating masses give the engine its playful and muscular character.
The laterally mounted balance shaft fulfills a dual function as it simultaneously drives the water pump. Thanks to perfect balance and reduced oscillating masses, engine vibrations are reduced to their simplest expression.
ENGINE MANAGEMENT SYSTEM
Keihin electronic fuel injection engine management system features a 44mm throttle body. Thanks to the unique position of the injector, the engine response is instantaneous. And for added convenience, you have independent adjustment systems for cold start and idle. The ultra-light control unit manages a unique traction control and start-up control system to give you a healthy boost in the event of difficulty and optimal traction thanks to the different engine maps adapted to the gear. triggered. A more powerful engine mode, selectable by means of the switch located on the handlebars, even makes it possible to reinforce the aggressive character of your machine.
The KTM 250 SX-F uses a CSS (Coil Spring Steel) clutch developed by KTM; It features a sturdy steel clutch housing, high heat resistance clutch discs and new, less wear-resistant nitrate-treated steel liners. The clutch is activated by a hydraulic system manufactured by Brembo, which plays an essential role in the progressiveness and flexibility of the clutch..
KTM’s proven integrated cooling system circulates the coolant from the cylinder head through the frame triangulation to the aluminum radiators supplied by WP. Its incredible efficiency is due to the better management of internal air flow and the progress made in ventilation thanks to CFD calculations (numerical simulation in fluid mechanics). The new radiator guards offer the advantage of better heat dissipation. This is all the more true in the presence of mud. Integrated into the front part of the spoilers, these radiator guards are particularly useful in the event of an impact.
The main objective of the KTM engineers during the development of the new generation SX was very significant weight reduction and improved handling. The result is clear: the current SX-F models are among the lightest and slimmest competition motorcycles on the market, although the 4-stroke are now equipped with a very beneficial electric starter, while competing models still have to. be kicked off. This is a sign that a strong current is flowing between the motorcycle and its rider.
The high-tech chromium-molybdenum steel frame, a model of lightness, flexibility and maneuverability, offers excellent stability and proves devilishly precise in the turns. Thanks to its high torsional rigidity and low longitudinal rigidity, this frame allows better absorption of the energy generated by the front and rear suspensions when jumping or crossing a bump. Driving is more comfortable and less taxing. The aluminum brackets that provide the link between the cylinder head and the frame are still just as light. Mounted laterally, they also help to limit the level of vibration and to refine the trajectory of the motorcycle in the bends. Engineers can be proud of their work because the frame is now a kilogram lighter than the lightest competitor frames available on the market today. Everything has also been done to facilitate maintenance and free up space for the tank and other components. The ultra-light rear part of the frame, made of stable aluminum profiles, weighs less than 900 grams on the scale.
Respecting the sound emission levels recommended by the FIM is a real challenge for all manufacturers. This is the reason why KTM has spared no efforts to develop an exhaust system at the forefront of innovation in this field. All 4-stroke are fitted as standard with exhaust manifolds connected to a small additional chamber called a resonator. They are also fitted with a relatively short silencer mounted as close as possible to the engine. This has a dual interest: better centralize the masses and enhance driving pleasure. The internal design has also achieved a significant degree of sophistication to keep the sound level well below the recommended thresholds, while ensuring maximum sensations for the pilot..
Sophisticated ‘zero dirt’ footrests prevent soiling of the pivot, even when going through deep ruts. The driving position is not high enough? Never mind! The footrest mounting system of the EXC models of the AM 2018 has been raised by 6mm compared to that of the SX versions.
AIR FILTER BOX
The air filter housing reinforces the protection of the air filter against contamination and guarantees optimum air flow. The cage in which the extra-large Twin Air air filter is housed is completely rigid, which helps to better hold the system in place. The design is so simple that one could replace the filter even with the face covered in mud. And this without the help of any tool. And in a matter of seconds.
When it comes to handlebars, KTM engineers have always known which direction to go. Contoured and made of high resistance aluminum, this handlebar is no exception to the rule. It is equipped with rubber shock absorbers and can be adjusted to two positions. The ODI handle is very practical to change if necessary, thanks to its mounting system without glue or wire.
In addition to significant weight savings, cast aluminum has ideal bending behavior. The one-piece molding process eliminates the imperfections inherent in welding and guarantees a more consistent build quality, but also more careful.
The ultra-light polyethylene tank has a capacity of 7 liters. Tank cap with internal thread ensures easy and reliable closing.
When it comes to wheels, KTM engineers know a thing or two about them. Equipped with ultra-light CNC machined hubs and premium Excel rims, these wheels guarantee maximum stability despite a limited weight. They are fitted with the latest generation Dunlop Geomax MX 3S tires
Another interesting novelty on this bike is the WP AER 48 inverted fork with air spring and separate damping circuits, developed by WP in close collaboration with KTM. The damping functions are on the right, the air spring is on the left. The left fork leg has a dual chamber and air cartridge system to prevent pressure loss. Should the outer seal ever leak, the pressure exerted inside the inner cartridge will hold the motorcycle in position. The air spring is easily adjusted according to the weight of the pilot using a single valve. No special tools are required – the standard pump will do. The right fork leg incorporates a cartridge specially designed to adapt to the type of damping sought. Just turn the 30-screen dial to the desired position (compression up and rebound down) to choose the appropriate setting based on track conditions and rider preferences. More comfortable and more sensitive than ever, this fork (with revised damping characteristics) is just waiting to be put to the test.
High quality CNC machined triple trees, which ensure ultra-precise front end behavior, have been a KTM hallmark for years. Two positions are possible for the handlebar trigger guard with shock absorber pads. Hourmeter indicates when it’s time for a service.
The WP shock absorber has been developed taking into account the architecture of the frame and the swingarm, just like the linkage system and the WP AER 48 fork. With its various machined and black anodized components, this ultra-sophisticated shock absorber is strong. impression compared to competing products less well finished. It benefits from a new setting that inspires confidence and optimized damping characteristics that go hand in hand with the setting of the front end. The shock features shiny colors, hallmarks of the WP brand.
These little jewels of technology are associated with Wave brake discs renowned for their lightness. More responsive, more efficient and more powerful than ever, Brembo brakes will tackle any situation.
POWER CURVE CHANGE BUTTON ON THE HANDLEBAR
All 4-stroke models have a power curve change button·on the handlebars, which fulfills the following three roles: Activation of traction control – Activation of the start control – Selection of an alternative power curve (Standard or Advanced). Traction control is a feature found on no other competitive model to date. It ensures more efficient traction when track conditions leave something to be desired. At the push of a button, you’re done. This power curve change button also enables the start control to be engaged. But a successful start and it is the holeshot assured. The principle of operation is simple: The start control reduces the maximum speed of the engine at the precise moment when you take off to maintain better control of the machine. Pressing both buttons when the engine is idling and the EFI warning light located on the upper triple clamp comes on to warn that the car is in READY TO RACE mode. In addition to the standard engine maps, there is another even more powerful engine mode. The future is on.
BATTERY AND WIRING HARNESS
The starter is associated with a powerful lithium ion battery, which represents a significant weight saving compared to before. To avoid being hampered by the electrical circuit when removing the buckle, the battery and wire harness are grouped together in a compartment above the air filter housing. Mechanics and DIY enthusiasts will appreciate.
Like all KTM 4-stroke motorcycles, the 250 SX-F is started at the push of a button, which is a definite advantage when it comes to setting a new stopwatch..
All the KTM factory riders collaborated on the design of the bike with the R specialists&D KTM and the Kiska design agency, with a single watchword: to create a perfect harmony between the rider and the machine. As much to say it immediately, the result is convincing. The ergonomics and the contact points for the pilot have been particularly taken care of to reinforce the freedom of movement and the comfort on the SX-F. The particular shape of the front and rear mudguards guarantees maximum stability and minimum weight, thanks to a well-thought-out structure and assembly. Better yet: they stay clean longer.
Custom graphics kit, Factory orange frame: every detail counts, because in this discipline, there is nothing more beautiful than a racing car that stands out from the rest.
Info and image credits: KTM
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250 SX-F 2017
Model marketed in
The technical aspect
2018 KTM 250 SX-F
- Tank: 7 liters
- Wheelbase: 1,485 mm
- Dry weight: 98 kg
- Train before
- secondary by chain
- Rear axle
(78 x 52.3 mm)