KTM is still investing in its ever-popular two-stroke program, as evidenced in its all-new 125/150 SX models. As with the thumpers, these machines feature lighter, more compact engines that weigh 4 pounds less than last year. Numerous internal changes—ranging from reshaped cylinders and pistons to physically narrower (same gear ratios) 6-speed transmissions grace both two-strokes, while the exhaust pipe on each has been upgraded for maximum power. The list of changes to these machines’ chassis is surprisingly similar to the SX-F models; the new frames have been designed to offer better energy absorption, the subframe/swingarm/footpegs are now lighter, the handlebar clamps are finally rubber mounted, and the ergonomics and bodywork have been altered to keep weight down and improve handling.
Along with the machines being lighter than ever, the 150 SX’s motor couldn’t be any more perfect for the chassis. It has a great bottom end hit that is really manageable and that pulls all the way to the top end without ever signing off. We could not believe how much power they squeezed into this little two-stroke! The 125 SX-F is similar, with crisp initial power that ascends into a full scream as you climb the revs. The buck 25 doesn’t seem to rev as high as the 150, but it did feel easier to keep in the peak power, as if the window was slightly bigger up top. Both bikes beg you to work the clutch around the entire track while just letting the motor sing.
No longer are these machines only for teenagers; our testers actually felt really comfortable with the suspension set up on the 150. Both front and rear, the initial part of the stroke offers that plush, progressive feeling as well as the controlled action that you need over the smaller bumps, but it also has the hold up needed to stay up in the stroke through moderate-sized braking bumps. The bike would bottom whenever we mistimed a rhythm or slammed too hard into a corner, but a big part of the lack of bottoming is the low overall weight of the motorcycle.
KTM’s two-stroke motocross models are among our favorite bikes to test—period—and you can bet your last tear-off that we’ll be spending more time aboard these machines before the year is up. Keep your eyes peeled for a more in-depth evaluation of these sweet machines in an upcoming issue of Dirt Rider.
