KTM 150 SX (2016–2022): A Two-Stroke Motocross Legend Reimagined

Introduction

The KTM 150 SX isn’t just a motorcycle—it’s a statement. From 2016 to 2022, this Austrian-engineered two-stroke dominated the 125–150cc motocross segment, blending lightweight agility with the raw, unfiltered thrill of a high-revving two-stroke engine. Designed for riders who crave precision and explosiveness on tight tracks, the 150 SX carved a niche as a “big bike in a small package.” After a day of ripping through berms and testing its limits, it’s clear why this machine remains a favorite for competitive riders and weekend warriors alike.

Let’s dissect what makes this generation of the KTM 150 SX a standout—and why it’s still relevant for motocross enthusiasts today.

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Engine Performance: Two-Stroke Fury, Modern Refinement

At the heart of the KTM 150 SX lies a 144cc liquid-cooled two-stroke engine. Unlike its tamer four-stroke cousins, this powerplant delivers a visceral riding experience characterized by instant throttle response and a screaming top-end rush. The Mikuni TMX 38mm carburetor (consistent across all model years) ensures crisp fueling, though it rewards riders who take the time to fine-tune jetting for their local conditions.

Key Highlights:
- Power Delivery: The engine builds power linearly until 7,000 RPM, after which it explodes into a frenzied crescendo. This “light switch” effect is classic two-stroke, demanding precise clutch control but rewarding aggression.
- Gearbox: The 6-speed transmission is slick and forgiving, with a Brembo hydraulic clutch offering featherlight lever action—critical for managing power during tight corner exits.
- Weight Advantage: At just 87.5 kg (193 lbs) dry, the 150 SX feels like a bicycle compared to four-strokes in its class. This translates to effortless flickability mid-air and quicker direction changes.

Riding the 150 SX on a sandy track reveals its genius: the engine’s hit is manageable enough for intermediate riders but explosive enough to keep experts engaged. It’s a bike that punishes laziness but rewards skill—a true teacher of throttle discipline.

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Chassis and Handling: Precision Meets Durability

KTM’s chromoly steel central-tube frame (25CrMo4 steel) has been a constant through this generation, offering a stiff yet forgiving foundation. Paired with CNC-machined hubs and Excel rims, the chassis strikes a balance between MXGP-level rigidity and trail-friendly compliance.

Handling Dynamics:
- Wheelbase: At 1,485 mm (58.5 inches), the bike feels planted in whoops but remains nimble enough to slice through rutted corners.
- Ergonomics: The seat height ranges from 850–960 mm (33.5–37.8 inches) depending on the year, accommodating shorter riders without sacrificing ground clearance (375 mm / 14.8 inches).
- Flickability: Throwing the 150 SX into a flat corner feels like guiding a scalpel—minimal input yields maximum results. The low weight and centralized mass make it almost telepathic.

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Suspension: WP’s Track-Tuned Mastery

KTM’s partnership with WP Suspension shines here. The 48mm USD front forks (AER 48 in early models, XACT-USD post-2020) and linkage-equipped rear shock are calibrated for motocross brutality.

Setup Notes:
- Front Travel: 310 mm (12.2 inches) of travel soaks up landing impacts effortlessly. The AER air fork in pre-2020 models allows for easy preload adjustments sans tools.
- Rear Suspension: The WP XACT Monoshock (post-2020) offers a broader range of high-/low-speed compression tuning, ideal for adapting to hardpack or loamy conditions.

During testing, the suspension handled everything from sharp square-edge bumps to G-out jumps with minimal drama. Beginners might find the stock setup stiff, but for aggressive riders, it’s a godsend.

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Brakes: Brembo’s Bite

The 150 SX doesn’t compromise on stopping power. Up front, a 260mm disc paired with a four-piston Brembo caliper delivers relentless bite, while the rear 220mm disc and two-piston setup prevents lockups during chaotic descents.

Rider Tip: Swap to sintered brake pads (available at MOTOPARTS.store) for enhanced durability during muddy races.

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Competition: How the 150 SX Stacks Up

The 150cc two-stroke class is fiercely competitive. Here’s how the KTM battles its rivals:

1. Yamaha YZ125

• Pros: Legendary reliability, smoother power delivery.
• Cons: Heavier (94 kg / 207 lbs), less adjustable suspension.
• KTM’s Edge: The YZ125 feels dated beside the KTM’s modern chassis and Brembo components.

2. Husqvarna TC 125

• Pros: Nearly identical engine to KTM, Magura hydraulic clutch.
• Cons: Higher seat height (960 mm / 37.8 inches), premium pricing.
• KTM’s Edge: The Husky’s composite subframe adds weight; KTM’s steel frame feels more direct.

3. TM MX 125

• Pros: Hand-built Italian craftsmanship, potent engine.
• Cons: Scarce dealer network, expensive parts.
• KTM’s Edge: Accessibility. TM’s exotic appeal can’t match KTM’s aftermarket and tuning ecosystem.

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Maintenance: Keeping the 150 SX in Fighting Shape

Two-strokes thrive on meticulous care. Here’s your maintenance cheat sheet:

1. Engine Rebuilds

• Piston Replacement: Every 30–40 hours for racers; 50+ hours for casual riders. Consider a Vertex forged piston (available at MOTOPARTS.store) for extended lifespan.
• Carb Tuning: Clean the Mikuni TMX jetting monthly. A JD Jet Kit eliminates guesswork for altitude/temperature changes.

2. Suspension Servicing

• Fork Oil Change: Every 50 hours. Use Motorex 5W for consistent damping.
• Shock Linkage: Grease bearings every 15 hours to prevent costly wear.

3. Air Filter Care

• Cleaning: After every ride. Twin Air filters with No-Toil biodegradable oil simplify the process.

4. Chain & Sprockets

• The 14:50 gearing is perfect for most tracks, but swap to a DID 520ERT2 chain for longevity.

5. Cooling System

• Use Engine Ice coolant to prevent overheating during summer motos.

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Conclusion: A Two-Stroke for the Discerning Rider

The KTM 150 SX (2016–2022) is a masterclass in focused motocross engineering. It’s not the easiest bike to ride—it demands respect, skill, and maintenance—but few machines deliver such a pure connection between rider and terrain. Whether you’re chasing holeshots or honing your skills, this KTM remains a benchmark in the small-bike arena.

For owners looking to elevate their 150 SX, MOTOPARTS.store offers everything from performance exhausts to gripper seat covers. Because even legends can use a little upgrade.

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Specifications sheet

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