Flying high: KTM continues to build on its tradition of monster 125cc engines with the '03 125SX.
Ever since its introduction several years ago, the 125SX has been known as "the fast one." Our experience on the 2003 model proves that fact hasn't changed. KTM knew its motor was the class leader and only made minor changes for '03. The biggest engine revision is the new center cases, as the KTM 125 formerly shared cases with its 200cc brother. KTM says the reduced volume in the new cases increases torque, and we have no problem believing that claim. KTM has followed the lead of a few other manufacturers and lopped off sixth gear in favor of a 5-speed box that is lighter. The transmission also receives a new aluminum gear-selector drum to ease shifting.
The new WP fork is 2mm larger in diameter than the 46mm legs of the others in the test and has the nice feature of external preload adjustment. The rear suspension is KTM's unique linkage-less design that has the shock mounted directly to the swingarm. The shock gets a larger reservoir and increased oil capacity for less fading, and has a top-out spring with 15mm of negative travel at the rear axle.
Efforts were made to make the little SX feel smaller. The subframe is lowered 5mm at its frame mount, which translates into 15mm at the rear of bike. The triple-clamp offset has been reduced from 20 to 14mm, which has a number of effects. First, the wheelbase is reduced, which has the effect of putting more weight on the front wheel. In addition, rake remains the same but
a bit of extra trail aids front-end feel. More beef has been infused by using stronger hubs and a 6mm larger front axle. The rubber hydraulic clutch hose is changed to a steel-braided line for durability, and like the rest of KTM's SX lineup, comes stock with a 10mm shorter Renthal tapered handlebar instead of Magura Bulge Bars. Finally, the bike has all orange plastic now, including the tank and rear fender, which looks much better the variety of bodywork colors formerly used.
The motor is insanely fast on the track, especially for a 125, and was rated tops by three out of the four test riders, and second on the other (Ewing gave the RM top spot). It has so much steam that it's hard to believe you're riding a 125. The bottom is a little soft compared to the Honda and Kawasaki, but after that, it's over.
The midrange hit is awesome and the bike pulls pretty well into the top of the powerband. We don't think you can make a much better 125cc powerplant, period.
The only major niggle in the KTM 125SX is the unique qualities of its linkage-less rear suspension.
The needle jet in the carburetor was changed to a 1470D (position 3), which is conveniently included in a jet kit with the bike. We really appreciate the fact that KTM sells the consumer a motorcycle that includes quality parts right down to the handlebars, chains and jet kits. While the rest of the bikes come stock with cheesy steel handlebars and weak chains, the KTM 125SX has incredibly strong, tapered aluminum handlebars and a high-quality Regina chain.Even more impressive is that the Austrian-made KTM retails for one dollar less than its Japanese competition.
KTM's linkage-less rear suspension has always handled the big hits well, but it has been criticized for its lack of plushness in smaller, repetitive bumps. To combat this, KTM's Tom Moen had already installed a slightly softer, progressive rear spring (from 7.1-9.5 to 6.6-9.1 kg/mm) on the bike. With this modification, the rear end of our SX was definitely more compliant in the rough and choppy terrain compared to other KTM motocrossers we have ridden, and yet it still retained most of its resistance to harsh bottoming. No complaints were made about the performance of its burly fork.
The KTM 125SX, as has been typical of European MXers, doesn't steer as quickly as most other bikes. However the KTM's new triple-clamp offset makes the SX steer better and more positively than before, while retaining its traditional stability at speed. Test riders loved the easy pull of the hydraulic clutch and the shifting action of the little nuclear pumpkin, and rated them both near the top of the class. The brakes, however, were perceived to be powerful but touchy, either on or off, and a few riders thought the rear was a bit spongy. Any way you slice it, because of KTM's incredibly versatile motor and competent chassis, the 125SX is a viable choice for beginners and pros alike.
