The KTM 125 SX is fitted with a robust 6-speed transmission. The gear ratios, which featured improvements and reinforcements, were carried over from the predecessor. The gearbox features a new drive shaft which uses a screw for front sprocket fixation and diaphragm spring instead of a circlip, ensuring optimal front sprocket fixation. Another highlight of the 125 SX transmission is the no-dirt gear shifter. Similar to the footpeg design, it prevents the build-up of dirt and ensures the next gear is always available, no matter what the conditions.