2023 · Motocross · Buyer's Guide
125 SX (MY2023)
The Rev-Hungry Stepping Stone
The Machine's Character
The 125 SX takes a rider off the minis and puts them on a full-size motocross track. This generation does it with fuel injection on a 125 cc two-stroke, and that matters more than it sounds. There is no jetting to chase when the morning is cold, the afternoon is hot or the track sits at altitude, because the engine meters its own fuel. The 41 hp comes from a small, rev-hungry motor in a steel double-cradle frame. It rides on an upside-down fork with 12.2 in (310 mm) of travel and 11.8 in (300 mm) at the rear, adjustable at both ends. Ride modes let a young rider tame the delivery while they learn.
This is KTM in its purest form: light, sharp and hard on lazy riding. You have to keep the engine singing, pick the right gear and carry corner speed, because there is no low-end torque to bail you out. That is exactly why it teaches so well. It ages well if you keep up with the service, and routine work is simple. The caveats are real, though. The green safety map can bog at random. The engine can detonate on pump gas, and with an aftermarket pipe it knocks even on race fuel. The ECU is locked, so tuners can't remap it. Buy it if you are a racer stepping up or a committed hobby rider who wants to learn to ride fast.
Hard Numbers
Spec sheets don't ride bikes, but they set the baseline.
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| Power | 41 hp (30 kW) |
|---|---|
| Displacement | 125 cc |
| Gearbox | 6-speed |
| Fork | Upside-down (USD) |
| Front brake | 260 mm |
| Ground clearance | 14.1 in (359 mm) |
| Front travel | 12.2 in (310 mm) |
| Rear travel | 11.8 in (300 mm) |
| Seat height | 37.7 in (958 mm) |
| Fuel capacity | 1.9 gal (7.2 L) |
Equipment check
Chassis
- Front Suspension Adjustable Standard
- Rear Suspension Adjustable Standard
Safety
- Ride Modes Standard
Known issues
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Unpredictable engine bogging in green safety map
The engine bogs unpredictably and randomly while operating in the safety engine map.
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Engine detonation on pump gas and race gas
The engine experiences detonation when running on pump gas, and the pinging or knocking worsens when paired with an aftermarket pipe and silencer, even when using race fuel.
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Locked ECU prevents aftermarket remapping
The factory engine control unit is locked from the manufacturer, preventing aftermarket tuners from remapping the machine.
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Rear shock rebound clicker is awkward to access
The rear shock rebound adjuster is difficult to reach by hand, requiring the use of a flat-head screwdriver to make adjustments.
The Numbers Compared
Compare the technical specifications of the KTM 125 SX with other bikes in its class.
Head-to-head: KTM 125 SX vs. its rivals
Power
Displacement
Seat height
Alternatives to the KTM 125 SX
If this one isn't quite the fit, these are the bikes worth riding back-to-back against it.
Any price note compares both bikes at the same age — the youngest age both have on the used market — against this KTM 125 SX. “cheaper/pricier” is what that bike costs second-hand, not how worn it is.
