KTM 85 SX (2016–2020): A Junior Motocross Powerhouse Tested

Introduction

The KTM 85 SX, produced between 2016 and 2020, is a motorcycle that needs no introduction in the junior motocross world. Designed for young riders transitioning from mini bikes to full-sized machines, this two-stroke screamer has carved out a reputation as a competitive, high-performance option for aspiring racers. With two wheel-size variants (17/14-inch "small wheel" and 19/16-inch "large wheel"), the 85 SX caters to riders of different heights and skill levels. After a day of thrashing this orange machine on a motocross track, it’s clear why it remains a favorite—even years after its release.

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Design & Ergonomics: Built for Aggression

The KTM 85 SX looks every bit the part of a race-ready machine. Its signature orange frame and black-and-white bodywork scream aggression, while the compact, central-tube double-cradle chassis keeps weight distribution razor-focused. The bike’s dry weight hovers around 67–68 kg (148–151 lbs), depending on the wheel configuration, making it easy for younger riders to maneuver.

Key Design Features:

• Adjustable Ergonomics: The small-wheel variant offers a seat height of 855 mm (33.7 inches), while the large-wheel version climbs to 890 mm (35 inches). Both are adjustable, ensuring a tailored fit as riders grow.
• WP Suspension Dominance: The 43 mm WP USD forks and WP PDS rear shock provide 270–300 mm (10.6–11.8 inches) of travel, striking a balance between plushness and track precision.
• Braking Confidence: Front four-piston calipers and rear two-piston calipers bite onto 210 mm (8.3-inch) discs, offering stoppage power that rivals adult bikes.

During my test ride, the bike’s narrow profile and grippy seat made it easy to shift weight mid-corner, while the footpeg placement encouraged an aggressive riding stance.

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Engine Performance: Two-Stroke Fury

At the heart of the KTM 85 SX lies a liquid-cooled, 84.9 cc (5.18 cubic-inch) single-cylinder two-stroke engine paired with a 6-speed gearbox. The Mikuni TMX carburetor delivers a sharp throttle response, and the powervalve-controlled exhaust ensures a broad powerband—critical for tackling jumps and tight corners.

Riding the Powerband:

• Low-End Punch: The engine pulls cleanly off idle, but the real fun begins at 8,000 RPM, where the power valve opens and unleashes a surge of acceleration.
• Top-End Scream: Revving out to 11,500 RPM, the bike feels like a rocket in straightaways. Shifting through the buttery Formula hydraulic clutch-assisted gearbox is seamless.
• Fuel Efficiency: With a 5.2-liter (1.37-gallon) tank, the 85 SX sips fuel, though premix oil (at a 1:40 ratio) is a necessary ritual.

On the track, the engine’s character is unforgiving but rewarding. It demands precise throttle control, especially in muddy conditions where rear-wheel spin is inevitable. For riders mastering clutch modulation, this bike is a perfect teacher.

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Handling & Suspension: Precision Meets Playfulness

The KTM 85 SX’s chassis is a masterclass in balance. The 24-degree rake and 1290 mm (50.8-inch) wheelbase provide stability at speed, while the lightweight frame allows for quick direction changes.

Suspension Breakdown:

• Front End: The 43 mm WP USD forks absorb braking bumps and landings with minimal drama. Adjusting compression is straightforward for tuning to track conditions.
• Rear End: The WP PDS shock eliminates linkage maintenance and delivers consistent damping, even during hard bottom-outs.

During my ride, the bike carved through berms like a knife and remained composed over rhythm sections. The large-wheel variant felt more planted at speed, while the small-wheel version excelled in tight, technical sections.

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Competition: How Does It Stack Up?

The KTM 85 SX faces stiff rivals in the 85cc class. Here’s how it compares:

1. Kawasaki KX85:

• Similar power delivery but uses a conventional fork setup instead of USD units.
• Slightly heavier at 70 kg (154 lbs).
• Less adjustability in suspension.

2. Yamaha YZ85:

• Air-cooled engine lacks the KTM’s liquid-cooled consistency during long motos.
• Softer seat foam and wider ergonomics suit beginners.

3. Husqvarna TC85:

• Shares the KTM’s engine and suspension but with a different aesthetic.
• Often priced higher with minimal performance gains.

The KTM’s edge lies in its WP suspension and hydraulic clutch, which offer a premium feel missing in competitors.

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Maintenance: Keeping the Orange Beast Alive

Owning a KTM 85 SX requires diligence, but its simplicity makes it manageable:

Key Maintenance Tips:

1. Two-Stroke Care:
2. Premix Religiously: Use a high-quality 2T oil at 1:40. MOTOPARTS.store offers synthetic options for cleaner combustion.

3. Piston Replacements: Inspect every 30–40 hours—common wear for high-revving two-strokes.

4. Suspension Servicing:

5. Rebuild forks and shock annually. Upgrade to MOTOPARTS.store’s aftermarket seals for dusty conditions.

6. Carburetor Tuning:

7. Clean the Mikuni TMX jetting monthly. Consider a JD Jet Kit for altitude adjustments.

8. Chain & Sprockets:

9. The 520 chain needs frequent lubrication. Replace sprockets if teeth show hooking.

10. Brake Upgrades:

11. Swap stock pads for sintered variants from MOTOPARTS.store for improved bite.

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Final Verdict: A Legacy of Winning

The KTM 85 SX (2016–2020) is more than a stepping stone—it’s a bike that shapes champions. Its combination of razor-sharp handling, explosive power, and premium components makes it a standout in the 85cc class. While it demands respect and maintenance, the rewards are endless: confidence on the track, skills honed, and a grin that lasts long after the engine cools.

Whether you’re rebuilding a used gem or upgrading your current ride, MOTOPARTS.store has the parts to keep your KTM 85 SX at peak performance. From piston kits to brake upgrades, we’ve got your back—because every future champion deserves a bike that’s ready to fight.

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Specifications sheet

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