The Aprilia RS4 125, sold simply as the RS 125 since 2016–2017, is a 125 cc sports bike made by Aprilia. The four-stroke RS4 125 replaced the extremely popular two-stroke RS 125 race replica in Aprilia’s range, and it is based on the four-stroke version of the Derbi GPR125.
Aprilia RS4 125 at a glance
| Shown | EICMA 2010; in production from early 2011 |
|---|---|
| Engine | electronically fuel-injected four-stroke, four-valve DOHC single-cylinder with balance shaft |
| Power | standard 15 bhp; a manufacturer race kit raises it to 25 bhp |
| Frame | die-cast aluminium perimeter frame with aluminium swingarm |
| Brakes | 300 mm front disc with a four-piston radial caliper; 220 mm rear disc |
| Fork (original) | 41 mm inverted fork with 110 mm of travel |
| Renamed | Aprilia RS (RS 125) with the model year 2017 range, Euro 4 |
| 2021 update | new styling, digital instruments, 140 rear tyre, full-LED headlights, Euro 5 and dual-channel ABS |
The English page says the bike has been sold as the RS125 since 2016; the Italian page says the new name came with the model year 2017 range, in production from spring 2017.
History of the Aprilia RS4 125
The RS4 series was shown at EICMA in 2010 and went into production in the first months of 2011. With it Aprilia continued its line of road bikes derived from its larger racing sisters, here the RSV4. The series was meant to stand beside and partly replace the RS range. As on the RSV4, the fairing shows off the frame and engine, with a triple headlight at the front and an LED tail light.
The chassis is an evolution of the previous RS with a new swingarm and an inverted fork of 41 mm and 110 mm of travel, with red and black anodised fork legs. Two displacements were offered: a 50 cc Derbi two-stroke single with oil mixer, and a 125 cc liquid-cooled four-stroke single from Derbi and Piaggio. In 2012 a special RS4 125 Replica was introduced, with graphics inspired by the RSV4 ridden by Max Biaggi and number 3 on the fairing.
Aprilia RS, from 2017
At the Cologne show in 2016 Aprilia presented the model year 2017 range, in production from spring 2017: the bike had a styling update in line with the RSV4 and the name changed to Aprilia RS. The RS 125 came first, with single-channel ABS on the front disc, a larger under-seat compartment and a Euro 4 engine, which added 4 kg to the weight. In November 2017 at EICMA the updated RS 50 with a Euro 4 engine replaced the RS4 50, and a limited-edition RS 125 GP Replica with RSV4-inspired graphics was introduced.
In 2021 the RS 50 left production and the RS 125 was updated: a new combustion chamber, new intake and exhaust ducts and an iridium spark plug to meet Euro 5, plus fully digital instruments with Bluetooth connectivity, a wider 140-section rear tyre, full-LED headlights and dual-channel ABS. For 2025 the bike got switchable traction control with an anti-rollover system, Euro 5+ approval and two new colours.
Design and features
- Engine: a fuel-injected, four-valve DOHC single with a balance shaft.
- Quickshift: an optional system like that of the RSV4, standard on the GP Replica, that cuts torque for clutchless upshifts.
- Chassis: a die-cast aluminium perimeter frame and an aluminium swingarm.
- Brakes: a four-piston radial front caliper on a 300 mm disc; Bosch single-channel ABS from 2017.
Aprilia RS4 125 versions
- RS4 125 and RS4 50 (2011): the first series.
- RS4 125 Replica (2012): graphics inspired by Max Biaggi’s RSV4.
- RS 125 (from 2017): the renamed Euro 4 bike, with a GP Replica edition.
- RS 125 (2021 and 2025): Euro 5 and Euro 5+ updates.
More Aprilia motorcycles are in our Aprilia collection, for example the RS 125 two-stroke, the RSV4 and the Tuono.
Aprilia RS4 125 questions and answers
What engine does the Aprilia RS4 125 have?
A four-stroke, four-valve DOHC single with fuel injection and a balance shaft, with 15 bhp as standard.
Is it related to the Derbi GPR125?
Yes, it is based on the four-stroke version of the Derbi GPR125.
What did the RS4 125 replace?
The two-stroke RS 125 race replica.
Can it be made more powerful?
A race kit from the manufacturer raises power from 15 bhp to 25 bhp.
Why did the name change?
With the model year 2017 range the RS4 became simply the Aprilia RS.
Video: Aprilia rs4 125 Sound Check Arrow exhaust (with and without Db killer) Walkarround FULLHD
Video by x4miiiz on YouTube.
Sources
- Aprilia RS4, English Wikipedia: engine, chassis, 2021 and 2025 updates
- Aprilia RS4, Italian Wikipedia: launch dates, 50 and 125 versions, renaming
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