In a dirt bike world now dominated by four-strokes, KTM not only adapts perfectly, but also offers a sweet remember of where it all began in the form of the 2009 KTM 125 SX. Highly competitive, this bike is all about lightness, chassis corner carving abilities and loads of torque obtained from a small in displacement and big in attitude two-stroke motor.

  • 2009 KTM 125 SX
  • Year:
  • Make:
  • Model:
  • Engine:
    Single cylinder, 2-stroke
  • Transmission:
    6 Gears
  • Horsepower @ RPM:
    40 hp
  • Torque @ RPM:
    19 ft-lb
  • Energy:
    Keihin PWK-S 38 AG
  • Displacement:
    124.8 L
  • Top Speed:
    100 mph
  • Price:



We can’t help noticing how, as much as four-stroke dirt bikes would evolve, the much smaller and equally (sometimes even greater) performing two-strokes manage to keep up with little effort. In the case of the 2009 KTM 125 SX, it is all about combining the advantages of a racing chassis (also used on KTM’s four-stroke dirt bikes) with those of the very light overall weight (only 200.2 lbs). On this year’s model, the seat is positioned at 38.78 inches (instead of 36.42 inches as on the previous model year) and the fuel tank capacity is of 2.11 gallons (instead of 2 gallons, like on the previous model year), not that this would do the 125 SX any good, but it’s the effect that the chassis, which was developed for bigger displacement bikes, has on it.

In what concerns the engine, this remains the same liquid-cooled, 124.8 cc, single-cylinder, two-stroke with an almost equal bore and stroke (2.13 x 2.15 inches). Carburetion is the solution to feeding all two-stroke engines and, in this case, we’re talking about a Keihin PWK-S 38 AG replacing last year’s Keihin PWK 39. Together with the new exhaust control, this is suppose to provide a wider spread of power all across the rev range, better throttle response and implicit make the bike more competitive. So does the six-speed gearbox, but that is nothing new.

2008 KTM 125 SX History


While last year we could at least mention the then previous model years of Honda’s CR125R and Suzuki’s RM125, we’re now left with the 2009 Yamaha YZ125 and 2009 Husqvarna CR125 as manufacturers gradually get rid of their MX2 contenders as these hardly pass emission regulations and are unfairly classified as being “dated”.

We’re happy to see that not all manufacturers consider so and we deal with what we have. So, as mentioned, the 2009 Yamaha YZ125 is a fierce competitor for the new 125 SX as the first is also characterized by overall lightweight (208 lbs) and a torquey 124 cc, liquid-cooled, two-stroke, reed-valve inducted engine. In this case, the seat is positioned even higher (39.3 inches). We’ve wrote about it so click on the previous links for more information.

2009 KTM 125 SX
- image 299419
2009 Husqvarna CR125

Husky offers a totally new 2009 CR125 powered by their also 124.8 cc large, liquid-cooled, single-cylinder, two-stroke engine that is mated to a six-speed tranny. This here is KTM’s biggest opponent and the two bikes have followed pretty much the same evolution so we’re expecting similar results from the Husqvarna CR125. The seat height in this case is positioned at 38.8 inches above the ground.


2009 KTM 125 SX
- image 299372
2009 KTM 125 SX

Although mainly addressed to entry-level riders, the 2009 KTM 125 SX is a full-size dirt bike with all the advantages that this implies. It is supposed to be a direct link from training bikes (which might be just as good for racing) towards the real thing and it looks just like that. Everything from the high mounted and sharp fenders, number plates and aggressive side panels as well as the narrow seat and Renthal handlebars are there to take first time contact with. This thing rolls on a pair of 21-inch front and 19-inch rear Excel wheels, but a 19-inch front wheel is also available for just in case that riders are expecting a smoother pass.

Frame and rims are black. So are the mudguards, seat and gas tank and yet we’re dealing with a fairly lively looking bodywork. It’s all due to the KTM orange, which is even present on the rear spring. The decals are nice too and, together with the white rear number plates, line the bike next to bigger models, be them two- or four-stroke.

Test Ride

2009 KTM 125 SX
- image 299370
2009 KTM 125 SX

After no more than a few track laps, we can’t help noticing how great performing this motorcycle actually is and start wondering if less experienced riders will feel at home on it as this thing speaks racing from it’s every nut and bolt.

First thing first, the engine is started after strictly following the kick starting routine: pull the choke, open the clutch a little bit and kick the starting lever for guaranteed success each and every time. No need to let it worm up as this is a two-stroke so there we go hitting first gear and making sure that we give the engine some gas before releasing the throttle for a quick launch, definitely comparable to what any modern 250 cc four-stroke competition bike will deliver.

As you can read, the thing with two-stroke engines is that they need to be revved or “kept in the zone”, as we like to call it and that requires a lot of gear changing. So it’s a good thing that the clutch pulls in easily and the gearbox is very precise. Sixth gear is rarely used on the track, but it’s a good thing for this bike to feature as most owners will also be wrapping it up for some off-road fun and that always takes a rider from hard breaking to reaching top speed in a short amount of time.

If ridden with caution and patience, the 125 SX will invite a starting rider to a jumping session (or is it the other way around?) and that’s when the true motocross velleities will be unveiled. The bike enjoys taking off with a fully opened throttle and, being light, will spend enough time in the air in order for the rider to become aware that he’s actually riding the hell out of his new bike. But, good lap times are all about keeping that rear wheel as much time as possible on the ground so smooth landings are ensured by the 48 mm WP USD forks offering 11.81 inches of travel and WP PDS shock absorber offering a greater 13.19 inches of wheel travel.

With the aggressive motocross riding position, handling comes natural and the 125 SX is among the most responsive and aggressive dirt bikes we’ve ever tested so you can imagine how much fun it can be even long after experience is accumulated.

Featuring 260 mm front and 220 mm rear wave-style disc brakes, this small displacement blast disposes of all the braking power needed to stop a 450 SX-F, not to mention its just over 200 lbs of weight. Let’s just hope that the rider isn’t chubby, but that’s not bad news at all because motocross will make him slim and fit.

It’s always a very exciting experience to ride a two-stroke motorcycle in generally as they are very unique rides and two-stroke dirt bikes in particularly simply because they are pure blasts with handling capabilities to match their engines impressive torque. The 2009 KTM 125 SX is a great representative of its class by showing a racy nature right after having brought a major contribution to the rider actually learning to exploit his aggressive riding side.


The 2009 KTM 125 SX starts at $5,998. This bike’s biggest advantage isn’t necessarily the price, but the fact that it won’t make a rider wish to ride something else for a very long time and that always saves money.


All in all, this is a bike that would make most two-stroke fans very happy and four-stroke ones eager to try out this new, small displacement, distinctive smelling and sharp cornering motorcycle built in Austria. We wish them good luck with that!


2009 KTM 125 SX
- image 299371
2009 KTM 125 SX


Engine and Transmission

Engine type: Single cylinder, 2-stroke
Displacement: 124.8 cc
Bore x stroke: 54 x 54.5 mm (2.13 x 2.15")
Starter: Kickstarter
Transmission: 6 gears
Carburetor: Keihin PWK-S 38 AG
Control: Exhaust control
Lubrication: Mixture oil lubrication 1:40
Transmission oil: Motorex, SAE 15W50
Primary drive: 23:73
Final drive: 13:50
Cooling: Liquid cooled
Clutch: Wet multi-disc clutch, operated hydraulically
Ignition: Kokusan

Chassis and Dimensions

Frame: Central double-cradle-type 25CrMo4
Subframe: Aluminium
Handlebar: Renthal, Aluminium Ø 28/22 mm (1.10 / 0.87")
Front suspension: WP USD Ø 48 mm (1.89")
Rear suspension: WP PDS shock absorber
Suspension travel front/rear: 300 / 335 mm (11.81 / 13.19")
Brakes, front/rear: Disc brakes 260 / 220 mm (10.24 / 8.66")
Rims, front/rear: 1.60 x 21"; 2.15 x 19" Excel
Tires, front/rear: 80/100-21"; 100/90-19"
Chain: 5/8 x 1/4"
Main silencer: Aluminium
Steering head angle: 63°
Wheel base: 1471 ± 10 mm (57.91 ± 0.39")
Ground clearance (unloaded): 390 mm (15.35")
Seat height: 985 mm (38.78")
Tank capacity: approx. 8 liters (2.11 gal)
Weight (no fuel): approx. 90.8 kg (200.2 lbs)

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