From 2012 the two-stroke SX 125 continued with the same Euro 3 reed-valve engine, six-speed gearbox and long-travel chassis shared with the RX 125.
| MODEL | APRILIA SX 125 2012 - |
| Year | 2012 - |
| Engine Type | Single cylinder, two-stroke, reed valve intake, Nikasil-lined aluminium cylinder (Euro 3) |
| Displacement / Capacity | 125 cc / 7.6 cu in |
| Bore X Stroke | 54 x 54.5 mm |
| Compression Ratio | 12.5:1 |
| Cooling System | Liquid cooled |
| Max Power | 16.4 kW / 22 hp |
| Max Torque | 16.0 Nm / 11.8 lb-ft |
| Ignition | Electronic CDI |
| Induction | Dell'Orto VHST 28 carburettor |
| Start System | Kick |
| TRANSMISSION SPECS | |
| Lubrication | Separate oil mixing |
| Gear Box | 6-speed |
| Clutch | — |
| Final Drive | Chain |
| CHASSIS SPECS | |
| Frame | High-strength steel double trellis beam and double cradle frame, separate seat subframe |
| Front Suspension | 40 mm upside-down telescopic fork, 260 mm / 10.2 in travel |
| Rear Suspension | Steel swingarm, hydraulic monoshock with piggy-back reservoir, 270 mm / 10.6 in travel |
| Front Brakes | Single 260 mm floating disc, Brembo 2-piston sliding caliper |
| Rear Brakes | Single 220 mm disc, 1-piston sliding caliper |
| DIMENSION SPECS | |
| Overall Length | — |
| Overall Width | — |
| Overall Height | — |
| Seat Height | 870 mm / 34.3 in |
| Wheelbase | — |
| Ground Clearance | — |
| Dry Weight | 115 kg / 254 lbs |
| Wet Weight | — |
| WHEEL SPECS | |
| Front Tyre | 110/70-17 |
| Rear Tyre | 150/60-17 |
| FUEL SYSTEM | |
| Fuel Capacity | 10 Litres / 2.6 US gal |
| Fuel Consumption | — |
| Top Speed | 132 km/h / 82 mph |
From 2012 the two-stroke SX 125 continued with the same Euro 3 reed-valve engine, six-speed gearbox and long-travel chassis shared with the RX 125. It was one of the last two-stroke 125 supermotos from a major maker before emissions rules pushed the class to four-strokes; the SX 125 name returned in 2018 on a four-stroke bike.
