We've said it time and time again, but KTM's continued development of its two-stroke model line is one of the things that make it a leader in off-road motorcycles. It seems like every few years the Austrian brand unveils their latest take on the premix burning bikes, something their lone Japanese competitor Yamaha has not done for over a decade. And for 2019, there is another all-new orange bike to discuss in the KTM 250 SX. Almost everything about the 250 SX, from the front fender to the rear fender, has been redeveloped or refined and the attention to detail is evident once a rider pulls the bike onto the track.
KTM's decision to design key components that are used across the various models in their full-size line might be the biggest reason the 250 SX receives so many changes so rapidly (the last "all-new" KTM 250 SX was in 2017). In order to keep performance near the same and production costs to a minimum, KTM implements similar chassis and suspension on the two-stroke and four-stroke model lines, a trend that continues with the new 250. For 2019 the engineers aimed to increase the rigidity and precision of the chassis through a new universally used chromoly steel frame, aluminum subframe, and a cast aluminum swingarm, which are paired to new engine hangers for the 250 SX. KTM could certainly have continued using the engine package from 2018, but instead the powerplant received plenty of updates that make it quite different from any orange 250 two-stroke that came before. The new die-cast engine cases place the clutch shaft four millimeters higher and the crankshaft 19.5 millimeters higher, two things that improve the mass centralization. Three of the most important engine pieces inside the cases are the counterbalancer, something that was first used in KTM's 2017 250 and 300 EXC, and the new rebalanced crank and crankshaft, which altogether greatly reduce the vibration of the engine through the motorcycle and to the rider. Matched to the engine cases is an updated cylinder that features a new exhaust that better flows fumes to the new expansion chamber and an external power valve adjuster that can mellow out or intensify the powerband of the engine. The changes to the engine cases also shift the engine placement one degree in the chassis in an attempt to put more emphasis on the front-end. A Mikuni TMX carburetor helps maintain the flow of air and fuel into the cylinder better thanks to the seven-degree rotation of the intake manifold that reduces the overflow of fuel. Another set of shared components that runs through all full-size motocross models in the KTM lineup is the WP AER 48 fork and corresponding shock, both of which received new settings that were aimed to improve the damping characteristics. Thanks to the aforementioned frame change, new body panels and fuel tank, CNC machined triple clamps that offer increased torsional stiffness and two positions of the rubber handlebar mounts for the Neken handlebars, and a slim seat with silicone ribs on the cover, the cockpit of the KTM 250 SX aims to allow the rider unrestricted range of motion. As always, KTM worked with top brands in the industry for the necessary components, including ODI for lock-on grips, Brembo for the braking units and hydraulic clutch system, Twin Air for the filter element, and Vertex for the piston.
As soon as you kick the KTM 250 SX to life, you can feel how much the counterbalancer and crank reduce the vibration of the engine. There are almost no arm-numbing tremors to be felt, no matter if you simply blip the throttle or hold it wide-open for a few seconds. This greatly helps the overall ride of the motorcycle, because the rider feels directly connected to the bike and can feel its every attribute, which in turn results in longer motos. As for the actual performance of the engine, the orange bike has a power profile unlike any other production two-stroke 250 we've tossed a leg over, thanks to a hearty low-end hit. If a rider can keep a finger or two on the clutch and gradually open up the throttle, they are rewarded with near four-stroke levels of torque. But if one gets too eager with the clutch and throttle, they can easily wind up looking at the sky due to powerful pull. Some riders raved about this initial response while others said they would detune this portion of the powerband with a gear change or adjustment of the external power valve adjuster, two easy changes that most riders will likely experiment over time. After the low-end hit comes a broad mid-range and this is really where the KTM 250 SX excels, because things happen in a hurry when a rider reaches this point. Due to the displacement, the sound emitted from the exhaust seems low and mellow, but really the engine is screaming and the speeds are very high, almost to the point that a rider might not be aware how fast they are actually going. Because of the potent low and mid-range some riders found themselves carrying gears much further than they expected, which meant they rarely reached the true top-end of the spread. Those that held the throttle on found that the top-end was a fitting finishing touch to the engine, but that it did lack a bit of over-rev when compared to the sensational low-end.
Anything we've ever said about the 2019 KTM chassis rings true with the 250 SX. Because KTM is the only major brand to stick with a steel frame, the bike has a very unique feel when it comes to hitting obstacles, as it feels extremely stable at speed and is forgiving over chop and hard landings. We felt equally confident carving through tight inside lines and blasting around sweeping berms, because the bike remained planted at all times and took direction without much resistance. Although there are riders that still have their qualms with the WP AER 48 fork and wish that KTM would follow the new trend of returning to traditional spring units, it's hard to knock the air-sprung units with the new damping settings and wide range of adjustment. Sure, some can detect a strange sensation when the fork moves through the stroke, but rarely did we hear complaints of a metal-to-metal clank or harsh action. The same smooth action applies to the rear shock, an area we've rarely critiqued since the switch to a linkage-equipped setup. As for the refined rider compartment, we have little complaints because it's very open and unrestrictive, all while allowing slight alterations for personal comfort. Our two critiques of the ergonomics are with the handlebars, because the tall bend of the Neken part is not well liked by our testing staff, and the slick feel of the seat cover.
We often hear that two-stroke development reached its peak right around the time that the majority of Japanese brands decided to drop the from their model lines. But after seeing the continued investment and feeling the results of KTM's efforts over the last few years, especially with the new 250 SX, it's very clear that there was plenty of potential left in the premix burning bikes. We feel that it will be difficult for KTM, or anyone for that matter, to top the 2019 machine and its robust engine package, supportive suspension, and agile chassis, yet we know they will continue to try and make more improvements.