KTM 125 SX
Although KTM has been building motocross bikes for many years, the lineup only received the “SX” designation in 1993. The name directly references the legendary American Supercross series (SX), where winning requires an extremely high-performance bike, both in terms of chassis and engine. These qualities perfectly reflect KTM’s slogan, “Ready to Race,” and over the years, the SX has become one of the most powerful bikes in its class.
The SX 125 has evolved significantly over time. KTM has always been committed to innovation. Notable examples include the introduction of the PDS rear suspension without linkage (launched in 1998 and discontinued in 2011), the hydraulic clutch, a true gamechanger in motocross before 2000, the highly versatile WP air fork, and even the introduction of fuel injection for 2-stroke engines.
Technical data KTM 125 SX 2025
Engine:
- Type: Single-cylinder 2-stroke engine, liquid-cooled, with exhaust valve
- Displacement: 124.8 cc
- Bore x stroke: 54 x 54.5 mm
- Piston: 2-ring
- Lubrication: Mixture 1:40 (2-stroke 100% synthetic oil, JASO FD standard)
- Intake: Reed valve
- Fuel injection: Keihin 39 mm electronic injection
- Clutch: multi-disc clutch (hydraulic Brembo)
- Starter: electric starter (lithium-ion battery HJTZ5S-FP-C 12V 2.0Ah)
- Spark plug: NGK BR10 ECMVX
- Gearbox: 6-speed gearbox (15W50 JASO T903 MA2 standard oil)
- Gear ratio: 13/51
Maintenance: KTM recommends changing the piston every 15 operating hours, at the same time as the transmission oil. All information on adjustment and maintenance can be found in the operating instructions.
Chassis:
- Chassis: Chrome-molybdenum steel tube / aluminum-reinforced polyamide rear frame
- Fork / suspension travel: WP XACT AER (air fork Ø 48 mm) / 310 mm → recommended oil: SAE 4
- Shock absorber / suspension travel: WP XACT LDS with deflection / 300 mm → recommended oil: SAE 2.5
- Front brake: 260mm brake disk
- Rear brake: 220mm brake disk
- Declared dry weight: 91.9 kg
- Seat height: 958 mm
- Front tire: 80/100-21
- Rear tire: 100/90-19
- Fuel tank: 7.2 l (98 unleaded fuel recommended)
Maintenance: KTM recommends changing the fork and shock oil every 45 hours of operation. All adjustment and maintenance information can be found in the owner's manual.
KTM 125 SX in our online store
In our store, we offer you high-quality parts quickly and at fair prices. For your KTM SX 125 you will find chain sets, fork seals and oil for regular maintenance as well as parts for customization: plastic kits, handlebars, grips, levers, etc.
