KTM 125 SX specifications
KTM · Motocross
It also describes a Factory expansion-chamber kit with special engine mapping that adds 2.5 hp and saves 15 percent of the weight of the standard exhaust parts, and improved engine mounts with cut-outs that reduce weight by 300 g and improve cornering.
KTM 125 SX
| Specification | Value |
|---|---|
| Model year | 2027 |
| Displacement | 124.8cc |
| Bore x stroke | 2.13 in x 2.15 in (54 mm x 54.6 mm) |
| Transmission | 6-speed |
| Ground clearance | 359 mm (14.13 in) |
| Weight without fuel | 92 kg |
| Starting MSRP | $8,449 |
| Class | Motocross |
| Engine | 1-cylinder, 2-stroke engine |
| Fuel system | Vitesco Technologies EMS |
| Final drive | 520, Non-sealed |
| Front suspension | WP XACT-USD (AER), Ø 48 mm |
| Front suspension travel | 310 mm |
| Rear suspension | WP XACT Monoshock with linkage |
| Rear suspension travel | 300 mm |
| Front brake | Disc brake |
| Seat height | 958 mm |
| Fuel capacity | 1.9 gal |
| Frame | Central double-cradle-type 25CrMo4 steel |
| Destination charge | $690 |
Where it sits in the range
The 125 SX costs $8,449, the cheapest of the full-size SX bikes, and $1,200 under the 250 SX. It weighs 92 kg without fuel, 7.4 kg less than the 250. The seat, fork and shock are the same as on the bigger two-strokes.
What riding one asks of you
A 125cc two-stroke motocross bike has a manual clutch and close-ratio gearbox. Compare the 125 SX’s engine size with the 250 SX and 300 SX in the specification table, then assess the rider’s experience and track requirements. A smaller displacement does not make abrupt throttle inputs safe.
Follow the fuel/oil mixing and service instructions for the exact SX model and year. KTM’s oil-injected XC-W models have different instructions from premix SX and XC machines.
The 125 SX suits a lighter junior or a skilled adult who enjoys a high-revving bike, and a rider who wants to learn to carry speed. A heavier or larger novice will find the 250 SX or a 250 F easier to live with.
125 SX against the YZ125 and 250 SX
Yamaha's YZ125 is the other current 125 two-stroke. The 250 SX is the next size up on the same chassis.
KTM 125 SX — specification referenceCycle World says ultralightweight handling and fast-revving, peaky power delivery make bikes like the 125 SX "easy to manage. But difficult to ride fast", and calls it an excellent training tool for young riders transitioning to the full-size ranks. Total Motorcycle gives the engine weight as only 17.86 kg (39.7 lb), and says it keeps its typical high-revving character while laying down grunt where it matters most.
KTM · Motocross
The 125 SX is KTM's smallest full-size motocross bike and a training tool for riders stepping up from the 85. Cycle World calls its power fast-revving and peaky, easy to manage but hard to ride fast, and KTM asks $8,449 before destination.
- Model-year range
- 2025–2027
- Compared editions
- 3
- Specification entries
- 21
- Entries that differ
- 1
2027 KTM 125 SX questions
Is the KTM 125 SX good for beginners?
Cycle World calls it an excellent training tool for young riders moving to the full-size range, though it says the peaky power makes it difficult to ride fast.
How heavy is the KTM 125 SX engine?
Total Motorcycle lists an engine weight of only 17.86 kg (39.7 lb). KTM lists the whole bike at 92 kg (203 lb) without fuel.
Can a 125 SX get more power?
Total Motorcycle describes a Factory expansion-chamber kit with special mapping that adds 2.5 hp and saves 15 percent of the weight of the standard exhaust parts.
The 125 SX costs $8,449, the cheapest of the full-size SX bikes, and $1,200 under the 250 SX. It weighs 92 kg without fuel, 7.4 kg less than the 250. The seat, fork and shock are the same as on the bigger two-strokes. So a rider who grows into a 250 SX keeps the same ergonomics and has only the engine to relearn. Ground clearance is 359 mm, 5 mm above the 250 SX.
A 125 two-stroke has little torque and rewards a rider who keeps the revs up, shifts precisely and carries speed through corners. That is why coaches use them for training: a mistake with the throttle costs momentum rather than throwing the bike sideways. The price is a busier gearbox and frequent clutch work, and a bike that feels slow to a heavier adult rider.
It also needs premix, spark-plug checks and regular top-end service, like any race two-stroke.
Other models in this reference: KTM 125 XC, KTM SX-E 5, KTM 1390 Super Adventure R.