It is powerful, light, agile and loves the racetrack. After all, it is what it was created for. Competing in the MX2 class, the KTM 125 SX is in for some stiff competition, but it relies on its two-stroke engine and optimized chassis to make a big point.
Riders who are searching for the most exclusive and powerful alternative to Japanese two-stroke motocross bikes are offered the 125 SX as the most advantageous solution that can show them the way to success when the dirt starts flowing. Even more, the small two-stroke engine can be put up against the biggest four-strokes in the business and still get out with a clean face.
It all started almost ten years ago when the 1999 KTM 125 SX was presented as a cross motorcycle fitted with a liquid-cooled, carbureted 124.80cc two-stroke engine which was mated to a five-speed transmission. Everything on the bike was as simple as it could get: disc brakes, front and rear, but no fancy suspensions. KTM launched the bike with a 7.5 litres (2 gallons) gas tank and this was never to be changed until this day.
In 2005 the bike received a new Keihin PWK 39 and Kokusan digital 2K-1 ignition. Despite these changes and also the adding of a wet multi-disc clutch, operated hydraulically, the 2005 KTM was lighter than its predecessor (203.7 pounds instead of 206.4 pounds).
2006 model year brought a complete redesign on the bike’s exterior look and the KTM Orange became darker. This is also the year when the rims were blacked out. But what’s most important is the fact that in 2006 the gearbox featured six speeds, making the bike an awesome performer on any kind of terrain and in any situations.
For the next year, the Austrian manufacturer had prepared an even meaner looking 125 SX, only to come back to KTM original Orange for 2008.
Filled with heritage and having a lot of AMA triumphs, the Honda CR125R is definitely among the best MX2 racing bikes as it relies on its 125cc liquid-cooled single-cylinder two-stroke with RC valve to deliver incredible two-stroke power and on its ultra-trick, aluminum-framed chassis technology to keep the bike as low as possible and handling as well as it puts down the power through its rear wheel.
Yamaha keeps the wait down on its YZ125 by bringing new refinements along with an aluminum frame housing and very compact 124cc, liquid-cooled, two-stroke, reed-valve inducted engine. We’re definitely talking about one of the most competitive two-stroke motorcycles in the class, but things aren’t necessarily supposed to stay that way.
Suzuki sees its way in this highly acclaimed class with the RM125, a motorcycle designed for the track and performing true to the expectancies. Fitted with a 124cc, two-stroke, single cylinder, liquid-cooled, AETC, crankcase reed engine, it offers the mid-range power needed to blast pass the competition. The wide powerband is here to keep the wheels spinning hardly so you’ll find the RM125 a strong opponent both of the KTM and the other Japanese motorcycles.
Not among the Japanese bikes, but well worth mentioning is the Husqvarna CR125. Having a 124.8cc, two-stroke liquid-cooled single w/ HTS power valve, the Husky engine is clearly designed to compete with KTM’s. Also, the six-speed gearbox gives a clue of what you’ll experience on this impressive ride. The riding feel is truly comparable to the one experienced on the KTM.
The look of a true motocross machine was what designers craved for and finally managed to succeed delivering. Customers are usually attracted by the aggressive plastics which are meant to individualize the KTM model on the motocross track.
The fenders are highly positioned reflecting the inches of travel and the seat is narrow so that the rider would find the perfect place to accommodate itself in order for it to feel the bike properly.
Front number plate is surrounded by the side panels covered in decals and the manufacturer’s name on each side. KTM combines Orange with Black for its most models, especially the ones destined for the off-road or the track so the fork, mudguards and Excel wheels are black.
Whenever testing a bike, I first focus on its engine in order to get a first and immediate idea of what I’m riding and this time I made no exception. Even more, the liquid-cooled124.8cc, single-cylinder, two-stroke engine received a reshaped piston for 2008 model year and KTM widen the powerband so I was highly motivated to keep doing so.
The engine delivers awesome mid-range power which lets at the rider’s disposal enough churn to pass away the competition, but what the retuning consists in, is the healthy top-end feel. Performance is the word in everyone’s minds as riding the KTM 125 SX and it is all due to the fact that the engine is perseverant all through the powerband and in all of its six gears.
Even though small, the motor pulls impressively strong and it can easily be compared with most 250cc four-stroke motorcycles out there. It is torquey down low, proves its best in the mid-range, and remains constant in the top-end. What backs up the motor is the six-speed transmission attached to it. You will quickly reach to the conclusion that the gearbox shifts smoothly and precise, making gear changes the easiest thing for riders who are still gaining experience and preparing for the full displacement blasts that KTM has to offer.
The suspensions which equip the new 125 SX are all-new WP and perform excellent for what riders search when jumping on a motocross bike. I could formulate no complains related to the 48mm adjustable fork which come with 11.8 inches of travel. It isn’t easy to bottom-up the front suspension and even when that will happen the resistance won’t let you know that you did so. But when something goes very well, something else should go a little less well and the strange thing is that in this case we are talking about the same unit: the fork. Given to its resistance, it is kind of hard to find the best trace in a fast curve and you will feel a bit insecure. The rear end is being taken care of by a monoshock featuring 13.2 inches of travel and the ride provided will be smooth and stable.
Even if the front suspensions are a little bit tricky, after getting used to the bike, you will feel like you’re doing the easiest thing when cornering. After all, we’re dealing with a KTM two-stroke motorcycle and this is where the manufacturer proves its best.
What never seems to go wrong on any KTM model is the braking equipment. Both discs are Brembo (260mm front, 220mm rear) and provide the needed stopping power for the rider to be a bit retained in applying them too sudden. I had the piece of mind that if I keep accelerating over my mental limit before a tight curve, I will rely on the performance brakes to slow me down significantly and live to fight another day. Excellent one, KTM!
Now that the Spring knocks at our doors riders begin thinking about buying new rides and the KTM 125 SX is often among them. Having an MSRP of $5, 498, it is definitely also among the bikes with the best bang for the buck. And what a bang!
Being reliable, maneuverable and impressively powerful, this KTM proves that the two-stroke age is far from being over. In fact, you’ll see more and more riders discovering that the four-strokes on which they started and evolved are incomparable with these strong-revving blasts that spread the dirt on motocross tracks all around the country.
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")
Transmission: 6 gears
Carburetor: Keihin PWK 39
Control: TVC power valve
Lubrication: Mixture oil lubrication 1:40
Transmission lubrication: 15W50
Primary drive: 23:73
Final drive: 13:50
Cooling: Liquid cooled
Clutch: Wet multi-disc clutch, operated hydraulically
Ignition: Kokusan digital magneto CDI
Chassis and Dimensions
Frame: Central double-cradle-type 25CrMo4
Subframe: Aluminium 7020
Handlebar: Renthal Aluminium Ø 28/22 mm (1.10/0.87")
Front suspension: WP USD Ø 43 mm (1.69")
Rear suspension: WP monoshock PDS
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"
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: 925 mm (36.42")
Fuel capacity: approx. 7.5 liters (2 gal)
Weight (no fuel): approx. 90.8 kg (200.2 lbs)