KTM recently released details on its 2019 SX model lineup with its trio of full-size two-stroke motocross bikes including the 125 SX, 150 SX, and 250 SX. Many of the model-specific changes for the 125 and 150 were to the engines, while the 250 received both engine and chassis revisions, and many of the updates to the chassis and suspension are shared among the three 2019 models.

2019 KTM SX Two-Stroke MX Models
The 2019 KTM 250 SX engine is raised in the frame by one degree around the swingarm pivot to improve the handling characteristics, specifically front wheel grip.Courtesy of KTM

Engine

Among the changes made specifically to the KTM 250 SX engine are a revised exhaust port for more precise function of the power valve to improve power delivery and a reworked water pump casing to optimize the flow of coolant. To allow for better airflow, KTM redesigned the airbox and intake snorkels and developed a new carburetor setting to work better with the two redesigned parts.

The 250 SX also has a more compact header pipe and muffler with new perforated inner tubes and lighter silencer packing to reduce noise. The new muffler equates to a weight reduction of approximately 300 grams (0.66 pound) from last year’s part. Lastly, the plastic bracket that secured the previous model’s mufflers is replaced by lightweight, welded mounting brackets on the 2019 machine.

2019 KTM SX Two-Stroke MX Models
The 125 SX, 150 SX, and 250 SX share many of the same updates for 2019, such as stiffer frames, updated suspension settings, and new bodywork.Courtesy of KTM

The 125 SX and 150 SX feature a host of changes shared between the two small-bore two-strokes. Both bikes feature a new cylinder with an updated layout of the exhaust port, a newly developed diaphragm steel (DS) clutch, and a new clutch cover that is lower and reduces the width of the engine by 10mm (approximately 0.4 inch), plus a new Pankl transmission.

The 125 SX and 150 SX also have a reworked carburetor setting and a new header pipe and muffler. Lastly, the muffler’s plastic mounting system is replaced by a welded aluminum bracket and the seat of kickstart intermediate gear has been reinforced for better reliability.

WP AER 48 fork
The WP AER 48 fork receives new damping settingsCourtesy of KTM

Suspension

KTM's 2019 two-strokes share the same suspension updates as the SX-F models, with the WP AER 48 fork receiving new damping settings and the WP shock getting an updated main piston and revised settings to match with the new fork setup and provide better damping characteristics.

WP shock
The WP shock gets an updated main piston and revised settings to match with the new fork setup and provide better damping characteristics.Courtesy of KTM

Chassis

KTM made a change specifically to the 250 SX frame for 2019 that raises the engine in the frame by one degree around the swingarm pivot to improve the handling characteristics, specifically front wheel grip. Another update is that the engine hangers (the connection between cylinder/head and frame) on the 250 SX are now made of aluminum instead of steel to improve precise cornering ability and reduce vibration.

Chassis changes shared among the three bikes include a new black frame with a 2-percent increase in longitudinal stiffness and a 10-percent increase in torsional stiffness. These increases in stiffness were done to improve feedback to the rider, offer more precise handling, and improve straight-line stability. The bikes have new frame guards with a structured surface, and the right frame guard also serves as a heat shield for the muffler.

2019 KTM SX Two-Stroke MX Models
The 125 SX and 150 SX share many of the same engine changes for 2019 including a new diaphragm steel (DS) clutch and a new clutch cover that is lower and reduces the width of the engine by 10mm (approximately 0.4 inch).Courtesy of KTM

The upper triple clamp has been revised and is stiffer to coincide with the new frame and flex characteristics of the latest WP AER 48 fork. The swingarm now has a longer rear axle slot that allows the rear wheel to be adjusted up to 5mm farther back than prior year models and the subframes are are 40mm (approximately 1.6 inches) longer to improve rear fender stability. The radiators have been redesigned and are mounted 12mm (approximately 0.5 inch) lower, and a redesigned coolant tube integrated in the frame triangle features a 4mm-larger center tube increasing the cross section by 57 percent. The gas tank has also been changed to improve the ergonomics.

2019 KTM SX Two-Stroke MX Models
Both the 125 SX and 150 SX have a redesigned airbox and intake snorkels, a new header pipe and muffler, and a reworked carburetor setting to work better with the new airbox and exhaust system.Courtesy of KTM

The final touches to the bikes are updated spoke nipples (designed to be more maintenance-free), new bodywork, a new seat shape, a revised bar pad and cover, and new graphics. Lastly, all KTM motocross bikes now come with a new triangle stand that also serves as a spacer for the front wheel for tying the bike down when hauling it in a vehicle. This reduces high static pressure on the air cartridge and prevents the fork from being compressed during transport.