wheels and overall design. The list of differences is relatively small. Displacement. The 150SX is 143.6cc. The 125SX is 124.8cc. Bore and stroke. The 150SX’s bore and stroke is 56mm by 58.4mm, while the 125SX’s is 54mm by 54.5mm. Gearing. More power can pull taller gearing, thus the 150SX has two fewer teeth on the rear sprocket (48t to 50t). Weight. Because the 150SX has a different bore and stroke, it is a little heavier than the 125SX. Parts. The crankshaft, cylinder, piston, power valve and rings are different. Clutch. The 150SX uses all steel drive plates, while the 125SX uses aluminum drive plates, except for two steel plates in the middle of the clutch pack. The 150 also has stiffer clutch springs. Jetting. The 150 has a leaner pilot jet than the 125, but since MXA changes the jetting on both bikes, it isn’t a factor. Q: WHICH BIKE MAKES THE MOST HORSEPOWER? A: No need to ask. At no point on the dyno curve did the 125SX come within three horsepower of the 2013 KTM 150SX. The 125SX peaked at 34. 66 horsepower at
11,200 rpm, while the 150SX hit 38. 83 horsepower at 11, 100 rpm. This power difference played out at every increment along the powerband (and was more than four horsepower from 9000 rpm to 12,000 rpm). Q: WHAT DO THE TWO POWERBANDS LOOK LIKE ON THE DYNO CURVE? A: To make the dyno numbers understandable, we will explain them in rpm increments. 7000 rpm: The KTM 150SX makes 17. 45 horsepower, while the 125SX is at 14. 90 horsepower. 8000 rpm: The 150SX two-stroke is producing 23. 37 horsepower at 8000 rpm, while the 125SX is making 20. 66 horsepower. 9000 rpm: At 9000 rpm, the 150SX is pumping out 29.07 horsepower compared to the 25. 37 horsepower of the 125SX. 10,000 rpm: The KTM 150SX makes 34.02 horsepower, while the 125SX is at 30. 20 horsepower. 11,000 rpm: Nearing its peak, the 150SX generates 38. 83 horsepower at 11 grand, while the 125SX is at 34. 37 horsepower. 12,000 rpm: The 150SX is still strong at 32. 97 horsepower, while the 125SX has dropped to 29. 20. Q: WHICH BIKE MAKES THE MOST TORQUE? A: The 2013 KTM 150SX two-stroke cranks out 18. 46 foot-pounds of torque at 10,900 rpm. That is a healthy number. The 125SX makes 16. 41 foot-pounds at 11,000 KTM 125SX VS. KTM 150SX
2013 KTM 125SX: At 34. 66 horsepower, the
KTM 125SX is a classic shriek engine. You
hold it on long and you hold it on hard.
Most MXA test riders preferred the 125SX’s
fluid power delivery to the burst of the