MXA MOTOCROSS 125 SHOOTOUT: 2011 KTM 150SX VS. 2011 YAMAHA YZ125 TWO-STROKE

July 2, 2011
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2011 KTM 1250SX.

Both the KTM 150SX and Yamaha YZ125 originated from the classic two-stroke gene pool, but thanks to gene splicing, borrowed technology and constant revisions, both machines have evolved into the fulfillment of the two-stroke promise. And, unlike most bikes that are compared to each other, these two bikes have grown more apart over the last few years?they are not “clonemobiles,” and it is possible that they aren’t even justly compared. The $6299 KTM 150SX and $6250 YZ125 may owe their genetics to the same family tree, but the fruit has fallen in distinctly different places. These are tests of the 2011 models…but the 2012’s don’t fall far from the tree. Although, we were forced to test the KTM 150SX against the YZ125 (because KTM didn’t import the KTM 125SX in 2011)?they will be importing the 125SX in 2012.

The MXA wrecking crew has spent the last few months running both machines back-to-back?not play riding or professional practice racing, but in true-to-life moto combat. Here is the fruit of our labor. It should be noted that these are both 2011 models (the 2012 Yamaha YZ125 will not be released for several months, so we elected to test  the 2011 KTM against the 2011 YZ125. The 2012 KTM 150SX is similar to the 2011 model, but with linkage suspension) 

Q: WHICH ONE MAKES THE MOST HORSEPOWER?

A: The KTM 150SX (actually 143.6cc) benefits from its 19.6cc displacement advantage, but more significant, the KTM engine has been redesigned more times as of late than the YZ125 mill. The extra development paid dividends that would make the KTM more powerful regardless?even if it was a 125.

Q: WHICH ONE IS FASTER ON THE TRACK?

A: The KTM is faster, thanks to 3 extra horsepower.


Getting down and dirty on the 2011 Yamaha YZ125.


Q: WHICH BIKE HAS THE BEST SUSPENSION?

A: The YZ125 has the best suspension by leaps and bounds. The YZ125’s spring rates are spot on, and the Kayaba SSS internals are terrific.

KTM hasn’t sat still in the suspension department. The 2011 150SX has a new frame, swingarm and shock position (and the 2012 model has the rising rate linkage from the 2011 four-strokes). The 2011 PDS shock was laid down and outfitted with an 11mm-longer shock (to work the frame’s new rising rate).

Q: WHICH BIKE HAS THE BEST JETTING?

A: The Yamaha YZ125 is jetted better (it went to Euro-spec jetting for 2011). We had to go much richer on the KTM’s mainjet to lessen pinging (182 to 190).

Q: WHICH BIKE HAS THE BEST BRAKES?

A: The KTM 150SX has the best brakes. This is no contest. Given the 200-pound weight of both the YZ125 and 150SX, even weak brakes work well, but KTM’s 260mm Brembo front brake is a thing of beauty. The YZ125’s 240mm Nissin front brake is just average.

Q: WHICH BIKE HAS THE BEST GEARING?

A: The Yamaha has better gearing, although most MXA test riders change the rear sprockets on both bikes. The KTM 150SX is more drastically overgeared than the YZ125

Q: WHICH BIKE HAS THE BEST GEARBOX?

A: This is a push. Both bikes have six-speed gearboxes and both work flawlessly.

2011 Yamaha YZ125.

Q: WHICH BIKE HAS THE BEST CLUTCH?

A: KTM’s hydraulic clutch self-adjusting and super reliable.

Q: WHICH BIKE HANDLES THE BEST?

A: The majority of MXA test riders lean towards the Yamaha YZ125’s geometry. Although the YZ125 isn’t quick or agile, it is very predictable. It tracks straight as an arrow and turns in with minimal understeer.

The KTM 150SX is no slouch, but it feels slightly unhinged on the entrance to turns (probably caused by its higher ground clearance).

In 2011 KTM only imported the 150SX, but for 2012 they will bring the 125SX back also.

Q: AND THE WINNER IS…

A: As unfair as it may seem, the 2011 KTM 150SX is the winner. In a class of machines where power is job number one, the bigger engine is number one.

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