2013 KTM 125 SX, Call today to make an appointment... 2013 KTM 125 SX IN A CLASS OF ITS OWN How can you identify future champions? By the bike they ride. The KTM 125 SX has been the springboard to a professional career for many a hungry young rider. And this will continue to be the case, what with new bodywork and significantly revamped suspension. Driven by the powerful 2-stroke engine with exhaust control system and 6-speed transmission, the lightest bike in its class has long been at the top of the pile.