The 2021 KTM 150 SX is an interesting take on the supercross and motocross categories. Using a special chromoly steel alloy, KTM’s engineers have managed to keep the weight of the 150 SX down, letting the extra power from the 150cc engine move it at speeds closer to a 250cc class competition bike, but with the agility and light handling of a 125cc.
The Austrian company actually developed the engine from the 125 SX engine, adding a little more bore and stroke to give it that extra punch. While there is no 150cc class in motocross competition, the 150 SX is often bought by trail riders and motocrossers to practice on for 250cc events without wearing out their primary bike.
The bike still includes the standard WP suspension, 6-speed multi-plate hydraulic clutch, and ultra-durable swingarm and frame that has been battle tested in the crucible of motocross. What is interesting about the WP XAct suspension on the 150 SX is that it is AER equipped, meaning that the right fork provides steering damping and moderate shock absorption, while the left fork is a full on air spring. This gives the bike extremely confident handling and a great addition to their offroad models for 2021.
The 2021 KTM 150 SX starts at $7,599 USD / $8,999 CAD.
On this page:we’ve curated specs, features, news, photos/videos, etc. so you can read up on the new 2021 KTM 150 SX in one place.
The pure exhilaration that this bike’s engine delivers warranted continued production. As it shares many of its key components with the class-leading 125, the cylinder, cylinder head and piston unit can now also be fitted on a 125 cc engine base, converting it to a 150 SX without having to replace the crankshaft. Compact and powerful, this innovative 2-stroke engine is a lightweight powerhouse that just makes perfect sense.
At the heart of the 150 cc engine is a 58 mm bore cylinder. It features an innovative power valve unit with a sophisticated mechanism designed for the lateral support exhaust ports. The exhaust port layout enhances engine performance, while the precise machining of the upper contour of the exhaust port ensures accurate port timing. The two component cylinder head works in complete harmony with the cylinder to deliver outstanding performance across the entire rev range.
The KTM 150 SX is fitted with a MIKUNI TMX 38 mm flat slide carburetor featuring settings that were adapted to suit the new airbox developed in 2019. For 2020, reworked reeds for intake reed block provide further improvements in function, sealing and reliability, ensuring the whole system is always providing smooth, controllable power throughout the rev range.
Crankcases and engine covers
The lightweight engine cases are manufactured using a high pressure die-cast production process, keeping wall thickness to a minimum while retaining strength and durability. The design allows for a high crankshaft position which is located near to the center of gravity, resulting in optimal mass centralization and easier rideability. The engine body is extremely compact, which contributes significantly to the low engine weight. Additionally for 2020, the kickstart intermediate gear has been reworked for improved reliability.
The KTM 150 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 pinion fixation and diaphragm spring instead of a circlip, ensuring secure pinion 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.
The frame is professionally crafted from hydro-formed chromium molybdenum steel tubes that are robot welded, ensuring the highest levels of consistent quality. The stiffness has been precisely tailored for the most dynamic handling, and works in perfect harmony with the suspension to provide nimble agility without losing high-speed stability. The frame also features “no dirt” footpegs, which have a simple but effective self-cleaning system that ensures the footpegs return to their original position, providing complete control in all conditions. All SX frames feature the same highly durable powder coating as the KTM Factory machines and come with standard frame protectors. The subframe is made from lightweight aluminum, providing rear fender stability and strong support for the rider at little extra weight.
The one-piece swingarm is manufactured using a gravity die-cast production process for exceptional strength at the lowest possible weight. It offers a wide range of adjustment for the rear wheel, allowing for a shorter wheelbase on tighter, twisty tracks, or a longer wheelbase for greater stability on longer, more choppy tracks. The swingarm’s chain measurement markings are visible from above, making adjustment simpler and more accurate.
All KTM SX models feature a seat that perfectly matches the range’s dynamic performance-oriented ergonomics. The seat cover features silicone strips that provide better feel and grip for the rider. The seat is conveniently fixed to the bike using one long, lateral screw, making it secure and easy to handle.
All full-size KTM SX models are equipped with the same high-strength aluminum tapered handlebar, made by NEKEN. The handlebar is fixed in rubber damped mountings, which allow for two different positions. The handlebars come standard with an ODI vulcanized grip on the right side and a comfortable ODI lock-on grip, which does not require any wire or glue, on the left. They also feature a bar-pad with a cover that can be attached and removed with little effort.