ID # 39461047

2026 KTM 125 SX

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FULL-SCREAM AHEAD

There are very few sounds that can't be beaten: the crack of a soda can on a blistering hot day, the ping of the perfectly executed golf shot, and the scream of a 125 cc 2-stroke full throttle. The KTM 125 SX takes its leads directly from the KTM Factory Racing team for pure performance, pure results. Like the sound it makes, you won't forget it.

Specifications

Model

Category Name

Motorcycles

Year

2026

Sale Type

New

Manufacturer

KTM

before the gate

Easy Suspension Adjustment

As always, the suspension boasts an easy tool-free setup at both ends, ensuring you chase down the podium in total control. On the rear, a hand-adjustable dual compression option allows riders to adjust high- and low-speed settings in a matter of seconds. The forks on the front end are also easily modified thanks to hand-adjustable clickers on the bottom of the fork shoe and top cap.

Electronic Fuel Injection

Pre-mix gets a remix across the 2-stroke KTM SX range, with Electronic Fuel Injection setting the standard. Now there's no setup pre-race. And thanks to the Keihin EFI and reed valve case design, you can be guaranteed of laying down optimal power at any altitude, all of the time. For 2026 there is a new fuel protector cap: you'll still have quick and easy access for maintenance but now more safety against any outside damage and accidental opening as well as preventing dirt from entering the sides of the connector.

Electric Start

Picture this; You're 7 laps into an absolute ripper of a race. You miss your line and end up stalling in a deep rut. But don't sweat it. All you do is press the starter button and you blast off again to take the flag. This is the reality on the KTM SX models. Thanks to a 12.8V 2 Ah lithium ion battery placed under the rider's seat, a high-quality starter and pickup, and super robust design, the only thing you'll be kicking - is ass.

Serviceability

The KTM SX and SX-F range is engineered and designed to provide riders with easy-to-access service parts, as well as suspension adjustability. This permits faster trackside and off-season maintenance, as well as simplifying motocross for novice riders without pit crews. For 2026, a new threaded radiator cap allows easier and faster opening with reduced force.

start strong

EFI + Power Valve

With EFI comes great rideability. Along with the electronic fuel injection is an electronic power valve on the KTM 125 SX, allowing for more usable power throughout the rev range. Smoother power means better traction. Better traction means holeshot heaven!

Performance

Designed to churn out torque, the KTM 125 SX is set to continue its dominance in its class with unrelenting forward momentum. The overall engine weight is only 39.7 lb (17.86 kg) and carries impressive horsepower figures. This lightweight powerplant retains its typical high-revving character while laying down the grunt where it matters most.

Selectable Maps

Once again slicing into the 125 cc class with the leading edge of technology, the KTM 125 SX features a map select switch allowing the racer to switch between 2 engine maps. The White Map - or Map 1 - provides a linear, predictable power delivery ideally suited to attack hard-packed dirt with a leaner air-fuel mixture. Alternatively, the Green Map - Mapping 2 - is tuned for loose, thick sandy conditions with a richer mix.

Factory Performance Kit

Give your KTM 125 SX a more bite with a 125 Factory Performance Kit. Comprising of upgraded engine parts, FMF exhaust, and special engine mapping, it provides a strong power increase across the rpm range.

calm under fire

Absolute Control

Get ready for a full-on berm assault. The KTM SX and SX-F machines received major frame updates directly from KTM Factory Racing efforts. For starters, the area around the rear shock mount is streamlined, with engine mounts and cut-outs for improved chassis flex. The front area of the frame has an optimum wall thickness with renewed engine mounts.

Ergonomics

Tank shrouds using bi-compound plastics channel air towards the radiators more efficiently, while a concise fuel tank roll, makes for a tighter, more secure fitment, reducing the chance of frame scrubbing and dramatically improving durability. All this works alongside the specially-developed rider triangle, to provide unmatched knee contact and gripping surfaces - especially when standing on the pegs.

hit the big stuff

Stability

The KTM Motocross range has a special rear brake pedal adding additional stiffness, bending resistance and braking feel to the overall package. At the other end, a forged steering head connection and CNC-milled triple clamps, make for the perfect alignment of the fork tubes. This precise geometry of the fork clamps ensures highly responsive and smooth fork action - not to mention unwavering stability when charging across ruts and onto the podium.

WP XACT Shock

Keeping things in check at the rear, the WP XACT rear shock for uses settings directly from the KTM Factory Racing Teams. The frame and shock geometry mean more ground clearance at the linkage, making it less susceptible to bottoming out. Small diameter linkage bolts save weight, while new linkage seals refine rear shock response and advanced damping characteristics.

WP XACT Fork

Let's get the technical parts out of the way first; the 48 mm WP XACT AER forks fitted to the KTM SX and SX-F line-up features a capsulated air spring and pressurized oil chamber for progressive and consistent damping, while oil and air bypasses reduce pressure peaks. In combination with the mid-valve damping system, all this provides exceptional feedback and rider comfort. The fork also has settings which not only compliment the frame and rear linkage, but ensures stellar performance at all levels. Speaking of settings, these are easily adjusted via a single air pressure pre-load valve, as well as easy-access click adjusters for compression and rebound. Additionally, the WP air pump needed to adjust the fork's air pressure is provided as standard in the buy-pack.

Tires

Getting power hooked into the dirt is a tough job. However, hours of research and testing have led the KTM Motocross range to the Dunlop GEOMAX MX34. Providing unmatched stability and control at the highest level, the rubber features a rigid carcass and rubber compound that improves damping and absorption, maintaining performance up to 30% longer than previous models. Progressive Cornering Block Technology also improves grip in the berms, while the rear pattern has a tall and wide center block for desirable traction and control everywhere else. Lastly, this unique block arrangement works to dispel mud buildup, ensuring traction in even the muddiest of track conditions.

maintaining momentum

Ground clearance

The shock absorber geometry on the KTM SX and SX-F machines gives decent ground clearance for the linkage, with the topology-optimized die-cast footpegs being less susceptible to hooking on deep ruts, and take-offs when scrubbing.

Consistency

Count on a durable chain guide and chain guard and minimize the chances of hooking on external objects - especially in extremely muddy terrain while reducing dirt build-up around the swingarm and rear sprocket. For 2026 we've also modified the fixing points and routing of the wiring harness so it's less prone to wear and damage.

Energy absorption

Besides the expertly crafted, hydro-formed, laser-cut, and robot-welded frame being engineered to provide exceptional rider feedback and straight-line stability, it consists of specifically calculated parameters of longitudinal and torsional flex. This means the frame acts as a "shock absorber" of sorts, making for a less harsh ride, resulting in less rider fatigue over many hard laps.

engine technical details

EMS

Vitesco Technologies EMS

Clutch

Wet multi-disc DS clutch, Brembo hydraulics

DESIGN

1-cylinder, 2-stroke engine

Clutch Type

DDS multi-disc wet clutch

DISPLACEMENT

124.8 cm³

TRANSMISSION

6-speed

Engine Stroke

2-Stroke

Primary Drive

23:73

Engine Cylinder

Single cylinder

Clutch Operation

Brembo hydraulics

FUEL-MIXTURE GENERATION

Keihin EFI, throttle body 39 mm

Clutch Primary Drive Teeth

chassis technical details

CHAIN

520, Non-sealed

REAR BRAKE

Disc brake

FRONT BRAKE

Disc brake

FRAME DESIGN

Central double-cradle-type 25CrMo4 steel

REAR SUBFRAME DESIGN

Aluminum-reinforced polyamide

suspension technical details

Rear Suspension

WP XACT Monoshock with linkage

Front Suspension

WP XACT-USD (AER), Ø 48 mm

Rear Suspension Setting

Compression and rebound adjustable

Suspension Travel (rear)

300 mm

Suspension Travel (front)

310 mm

Front Suspension Adjustment

Compression (high and low speed), rebound

dimensions technical details

Seat Height

958 mm

Ground Clearance

359 mm

Weight (without Fuel)

91.9 kg

Tank Capacity (approx.)

7.2 l

literature

Name	Link
Technical Specifications	Download

Documents

KTM-technical-specifications (5).pdf