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2018 KTM 125 SX Overview
For 2018, KTM offers the 125 SX as a cross / motocross motorcycle with 124.80 cc on tap. The 2018 KTM 125 SX is built around a Single cylinder, two-stroke engine. Internally, bore and stroke are 54 x 54.5 mm. In everyday use, the 2018 125 SX tips the scales at 87.2 kg, carries a 7-litre fuel tank, offers a seat height of 960 mm and spans a 1,485 mm wheelbase. Every technical detail, from suspension travel to tyre sizes, is covered in the full 2018 KTM 125 SX spec sheet below.
2018 KTM 125 SX compared with other bikes in the Cross / motocross category
Measured against other bikes in the Cross / motocross category in our database (up to 224 models, one entry per model), the 2018 KTM 125 SX comes out as follows.
- With 960 mm, the 125 SX has the joint 41st tallest seat height of 200 bikes in the Cross / motocross category, 7% above the category average of 901 mm.
- Engine displacement of 125 cc is smaller than that of 159 of the other 223 bikes in the Cross / motocross category.
- Narrowing the field to the 111 models within five model years of it, the seat height of 960 mm is taller than that of 67 of the other 110.
Versus the 2017 model
The figures we track are unchanged from the 2017 model: displacement and seat height all match.
2018 125 SX - Pros & Cons
Strengths
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🛑
Strong front braking: The single disc front brake bites hard and stays consistent - a solid foundation whether it's stock or upgraded with braided lines.
Considerations
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🔧
Carburetor fuelling: Carburetion is more hands-on than fuel injection - plan on periodic jetting and cleaning as part of routine ownership.
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📏
Tall seat height: A 960 mm seat puts flat-footing out of reach for a lot of riders - sit on it in person before committing.
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⛽
Modest fuel capacity: A 7-litre tank keeps things light but means budgeting for more frequent fuel stops on any longer ride.
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⚙️
Chain final drive upkeep: A chain drivetrain is the most common setup in its class, but it's also the one that demands the most regular hands-on maintenance.
Wear Points & Servicing Notes
Carburetor maintenance
Being carbureted, the 125 SX is more sensitive to stale fuel and altitude changes than a fuel-injected bike - a carb clean and rejet restores crisp throttle response after any extended lay-up.
Brake disc and pad wear
Single disc with Brake calipers on floating bearings up front provides the primary stopping power; inspect disc thickness and pad wear at each tyre change to catch scoring before it becomes a rotor replacement.
Suspension condition on used examples
Suspension duties are handled by WP-USD, AER 48, ? 48 mm up front and WP shock absorber with linkage at the rear. Weeping fork seals aren't a dealbreaker on a used bike, but they're a fair basis for negotiating price.
Final drive maintenance
Chain final drive on the 125 SX means routine lubing and tension checks are part of ownership - skip them and sprocket wear accelerates noticeably.
Frame & chassis check
The Chrome-molybdenum steel central-tube frame chassis holds up well with normal use; on a used bike it's still worth checking the head-stock and swingarm pivot area for impact damage or corrosion.
Low-speed handling
The 125 SX's 87.2 kg kerb weight makes low-speed control noticeably less effort than on a heavier machine.
125 SX - Buying & Maintenance Guide
What to check before buying
A pre-purchase check on the 2018 KTM 125 SX with its 124.80 cc cross / motocross should cover the same ground every time: service history, drivetrain condition, and any oil seepage around the casings. This model runs chain final drive, so check chain slack and sprocket tooth profile specifically - a worn sprocket is a cheaper fix now than after it's chewed up the next chain. Now 8 years old, this cross / motocross is as likely to show age-related wear (perished rubber, seized fasteners, degraded seals) as mileage-related wear. Start it from cold if you can - a well-kept 125 SX settles to a smooth idle within seconds.
Oil and filter changes
Oil changes are the cheapest insurance you can buy for the 125 SX's 124.80 cc single cylinder, two-stroke - keep to the manufacturer's interval rather than stretching it. Use the viscosity grade the manual specifies, not whatever's on sale.
Carburetor upkeep
A 125 SX that's sat unused is almost always a carb-cleaning job before it runs right again - float bowls and pilot jets first, since they clog before anything else.
2018 KTM 125 SX - Frequently Asked Questions
What engine does the 2018 KTM 125 SX have?
The 2018 KTM 125 SX uses a Single cylinder, two-stroke engine with 124.80 cc of displacement.
How much does the 2018 KTM 125 SX weigh?
The 2018 KTM 125 SX weighs 87.2 kg. This is the manufacturer's dry figure.
What is the fuel tank capacity of the 2018 KTM 125 SX?
The 2018 KTM 125 SX has a 7-litre fuel tank. At around 5-6 litres per 100 km, that is roughly 116-140 km between stops.
Is the 2018 KTM 125 SX suitable for shorter riders?
The 2018 KTM 125 SX has a seat height of 960 mm. This is towards the tall end of the spectrum and will require most riders under 175 cm to tiptoe at stops.
What brakes does the 2018 KTM 125 SX have?
The 2018 KTM 125 SX uses single disc with Brake calipers on floating bearings at the front and single disc with Brake calipers on floating bearings at the rear.
What fuel system does the 2018 KTM 125 SX use?
The 2018 KTM 125 SX uses Carburettor. Mikuni TMX, providing precise fuelling across the rev range and reliable cold-start behaviour.
What suspension does the 2018 KTM 125 SX have?
The 2018 KTM 125 SX uses WP-USD, AER 48, ? 48 mm up front and WP shock absorber with linkage at the rear.
KTM 125 SX Spec Evolution
The KTM 125 SX was produced across 21 model years (2003-2023). The table below highlights the key specifications that changed across the production run - useful whether you are comparing years or tracking down a specific variant.
| Specification |
2003 |
2004 |
2005 |
2006 |
2007 |
2008 |
2009 |
2010 |
2011 |
2012 |
2013 |
2014 |
2015 |
2016 |
2017 |
2018 |
2019 |
2020 |
2021 |
2022 |
2023 |
| Wet Weight |
- |
- |
- |
- |
- |
- |
- |
- |
104.0 kg / 229.3 lbs |
292.1 kg / 643.9 lbs |
- |
112.0 kg / 246.9 lbs |
- |
- |
- |
- |
- |
- |
- |
- |
- |
| Dry Weight |
93.6 kg / 206.4 lbs |
93.6 kg / 206.4 lbs |
92.4 kg / 203.7 lbs |
92.4 kg / 203.7 lbs |
92.4 kg / 203.7 lbs |
90.8 kg / 200.2 lbs |
90.8 kg / 200.2 lbs |
90.8 kg / 200.2 lbs |
88.8 kg / 195.8 lbs |
91.6 kg / 201.9 lbs |
90.8 kg / 200.2 lbs |
90.8 kg / 200.2 lbs |
90.8 kg / 200.2 lbs |
87.8 kg / 193.6 lbs |
87.2 kg / 192.2 lbs |
87.2 kg / 192.2 lbs |
87.5 kg / 192.9 lbs |
137 kg / 302.0 lbs |
87.5 kg / 192.9 lbs |
87.5 kg / 192.9 lbs |
92.4 kg / 203.7 lbs |
| Engine Detail |
- |
- |
- |
- |
- |
- |
- |
- |
- |
Reed intake and exhaust control |
Reed intake. |
Reed intake. |
Reed intake. |
Reed intake. |
Reed intake. |
Reed intake. |
Reed intake. |
- |
- |
- |
- |
| Engine Type |
Single cylinder |
Single cylinder |
Single cylinder |
Single cylinder |
Single cylinder |
Single cylinder |
Single cylinder |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
Single cylinder, two-stroke |
| Seat Height |
925 mm / 36.4 in. |
925 mm / 36.4 in. |
925 mm / 36.4 in. |
925 mm / 36.4 in. |
925 mm / 36.4 in. |
960 mm / 37.8 in. |
985 mm / 38.8 in. |
985 mm / 38.8 in. |
992 mm / 39.1 in. |
992 mm / 39.1 in. |
992 mm / 39.1 in. |
992 mm / 39.1 in. |
992 mm / 39.1 in. |
960 mm / 37.8 in. |
960 mm / 37.8 in. |
960 mm / 37.8 in. |
950 mm / 37.4 in. |
- |
850 mm / 33.5 in. |
950 mm / 37.4 in. |
958 mm / 37.7 in. |
| Fuel Capacity |
7.50 litres / 1.98 gallons |
7.50 litres / 1.98 gallons |
7.50 litres / 1.98 gallons |
7.50 litres / 1.98 gallons |
7.50 litres / 1.98 gallons |
7.50 litres / 1.98 gallons |
8.00 litres / 2.11 gallons |
8.00 litres / 2.11 gallons |
7.50 litres / 1.98 gallons |
7.50 litres / 1.98 gallons |
7.50 litres / 1.98 gallons |
7.50 litres / 1.98 gallons |
7.50 litres / 1.98 gallons |
7.00 litres / 1.85 gallons |
7.00 litres / 1.85 gallons |
7.00 litres / 1.85 gallons |
7.50 litres / 1.98 US gallons |
- |
7.50 litres / 1.98 US gallons |
7.50 litres / 1.98 US gallons |
7.20 litres / 1.90 US gallons |
| Stroke |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
2-stroke |
| Ground Clearance (mm) |
390 mm |
390 mm |
390 mm |
390 mm |
390 mm |
390 mm |
390 mm |
390 mm |
385 mm |
395 mm |
395 mm |
395 mm |
395 mm |
375 mm |
375 mm |
375 mm |
375 mm |
- |
375 mm |
375 mm |
359 mm |
Key Specifications
Engine
Single cylinder, two-stroke
Weight
87.2 kg / 192.2 lbs
Fuel Capacity
7.00 litres / 1.85 gallons
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Full 2018 KTM 125 SX Specifications
Colours
Orange/white/black
Ground Clearance (in.)
14.8 inches
Ground Clearance (mm)
375 mm
Seat Height
960 mm / 37.8 in.
Wheelbase
1,485 mm / 58.5 in.
Dry Weight
87.2 kg / 192.2 lbs
Fuel Capacity
7.00 litres / 1.85 gallons
Displacement (cc)
124.80 cc
Displacement (ci)
7.62 cubic inches
Engine Type
Single cylinder, two-stroke
Bore x Stroke (in,)
2.1 x 2.1 inches
Bore x Stroke (mm)
54.0 x 54.5 mm
Engine Detail
Reed intake.
Fuel System
Carburettor. Mikuni TMX
Ignition
Kokusan EMS
Starter
Kick
Clutch
Multi-plate clutch, Brembo hydraulics
Final Drive
Chain
Gearbox
6-speed
Primary Drive
13:50. Primary drive: 23:73.
Frame Type
Chrome-molybdenum steel central-tube frame
Suspension - Front
WP-USD, AER 48, ? 48 mm
Suspension - Rear
WP shock absorber with linkage
Rake
26.5°
Wheel Travel - Front
300 mm / 11.8 in.
Wheel Travel - Rear
300 mm / 11.8 in.
Brakes - Front Diameter (in.)
10.2 inches
Brakes - Front Diameter (mm)
260 mm
Brakes - Rear Diameter (in.)
8.7 inches
Brakes - Rear Diameter (mm)
220 mm
Brakes - Front
Single disc. Brake calipers on floating bearings
Brakes - Rear
Single disc. Brake calipers on floating bearings
Rims
CNC machined hubs. Excel rims. Wire spoked.
Specifications are compiled from manufacturer documentation and cross-referenced
technical sources, and corrected on an ongoing basis.
Spot an error? Let us know.
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