Motocross Bikes
2021KTM 125 SX
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The 2021 KTM 125 SX is a lightweight two-stroke enduro bike designed for young riders and beginners entering competitive off-road racing. Powered by a 124.8cc single-cylinder engine producing 15 horsepower, it delivers sharp acceleration and nimble handling ideal for motocross and trail riding. Known for its aggressive styling, responsive performance, and affordable pricing, the 125 SX remains a popular choice for developing fundamental riding skills in off-road disciplines.
- Capacity
- 124.8 ccm
- Engine
- Single, two-stroke
- Gearbox
- 6-speed
- Dry weight
- 87.5 kg
- Seat height
- 950 mm
- Power
- 15.0 HP (10.9 kW)
What’s new for the 2021 KTM 125 SX
vs the 2020| Spec | 2020 | 2021 |
|---|---|---|
| Front suspension | WP upside-down Ø 48 mm | WP XACT-USD, Ø 48 mm |
| Rear suspension | WP Monoshock | WP XACT Monoshock with linkage |
Other years
2003
2004
2005
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2008
2009
2010
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2012
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2018
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2021
2022
2023
2025
2026
2027
How it rides
Editorial estimate from the spec sheet - not lab tested- Best for
- Built purely for closed-course motocross racing, it excels at jumps, berms, and rapid direction changes on dirt tracks rather than any street use.
- Built for
- Light, explosive, and razor-sharp in handling, it rewards aggressive riding with a peaky two-stroke power band and minimal weight to manage.
- Not ideal for
- It is not suitable for commuting, highway travel, passengers, or riders seeking comfort, storage, or a forgiving low-end power delivery.
Scores are derived from the spec sheet using the same model across every bike, so they compare like for like.
Will it fit you?
Worked out in your browser - nothing is sent to usEngine
- Capacity
- 124.8 ccm
- Power
- 15.0 HP (10.9 kW)
- Engine type
- Single, two-stroke
- Power/weight ratio
- 0.1714 HP/kg (dry)
- Bore x stroke
- 54.0 x 54.5 mm
- Cooling system
- Liquid
- Fuel system
- Injection
- Starting
- Kick
- Ignition
- Kokusan EMS
- Lubrication system
- Wet sump
Transmission
- Gearbox
- 6-speed
- Transmission type
- Manual
- Final drive
- Chain
- Clutch
- Multi-plate clutch, Brembo hydraulics
Dimensions & weight
- Wheelbase
- 1489 mm
- Seat height
- 950 mm
- Dry weight
- 87.5 kg
- Fuel capacity
- 7.50 litres
- Ground clearance
- 375 mm
Chassis & suspension
- Frame
- Central double-cradle-type 25CrMo4 steel
- Front suspension
- WP XACT-USD, Ø 48 mm
- Rear suspension
- WP XACT Monoshock with linkage
- Front wheel travel
- 310 mm
- Rear wheel travel
- 300 mm
- Rake (fork angle)
- 26.1°
- Trail
- 120 mm
Brakes & wheels
- Front brakes
- Single disc
- Front brakes diameter
- 260 mm
- Rear brakes
- Single disc
- Rear brakes diameter
- 220 mm
- Front tyre
- 110-17
- Rear tyre
- 150-17
Other
- Color options
- White/Orange
Specs last verified against published sources: .
Compiled from manufacturer documentation and user contributions, corrected on an ongoing basis. Spotted something wrong? Tell us.
What changed, year to year
Differences highlighted| Specification | 2003 | 2009 | 2015 | 2020 | 2021 | 2027 |
|---|---|---|---|---|---|---|
| Capacity | 125 cc | 125 cc | 125 cc | 125 cc | 125 cc | 125 cc |
| Dry weight | 94 kg | 91 kg | 91 kg | 88 kg | 88 kg | 92 kg |
| Seat height | 925 mm | 985 mm | 992 mm | 950 mm | 950 mm | 958 mm |
| Fuel capacity | 7.5 L | 8 L | 7.5 L | 7.5 L | 7.5 L | 7.2 L |
Illustrative - generated automatically by diffing the year records already on file, not a manufacturer-published changelog.
Rider Reviews
Common questions
What is the engine size of the KTM 125 SX?
The 2021 KTM 125 SX has a Capacity of 124.8 ccm (7.62 cubic inches).
What engine power does the KTM 125 SX have?
The 2021 KTM 125 SX has a Power of 15.0 HP (10.9 kW).
How many gears does the KTM 125 SX have?
The 2021 KTM 125 SX has a Gearbox of 6-speed.
How much does the KTM 125 SX weigh?
The 2021 KTM 125 SX has a Dry weight of 87.5 kg (192.9 pounds).
Shop this bike
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The 2021 KTM 125 SX is a powerful and lightweight motocross bike that is perfect for riders looking to take their skills to the next level. With its high-performance engine and race-ready suspension, this bike offers unmatched agility and control on the track. The top-of-the-line components and advanced technology make this motorcycle a top choice for competitive riders who demand the best performance from their machine. Whether you're a seasoned pro or a novice rider, the KTM 125 SX delivers an exhilarating and responsive riding experience that is sure to impress.
In conclusion, the 2021 KTM 125 SX is a top-of-the-line motocross bike that offers exceptional performance and handling. With its powerful engine and race-ready suspension, this motorcycle is a top choice for competitive riders looking to push their limits on the track. Whether you're a seasoned pro or a novice rider, the KTM 125 SX delivers an exhilarating and responsive riding experience that is sure to impress. If you're looking for a high-performance motocross bike that delivers unmatched agility and control, the 2021 KTM 125 SX is the perfect choice for you.
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