Aprilia RS4 125

The Aprilia RS4 125 (sold as the RS125 since 2016)^[1] is a 125 cc class sportbike manufactured by Italian motorcycle firm Aprilia. The four-stroke RS4 125 replaces the extremely popular RS125 two-stroke race replica in Aprilia's lineup. The bike is based on the four-stroke version of the Derbi GPR125.^[5]

Aprilia RS4 125

Manufacturer	Aprilia
Also called	Aprilia RS125 (2016–present)[1]
Parent company	Piaggio
Production	since 2011
Predecessor	Aprilia RS125
Class	sport bike
Engine	124.2 cc (8 cu in) Single-Cylinder DOHC[2] four valve four-stroke Electronic injection
Bore / stroke	58.0 by 47.0 millimetres (2.28 in × 1.85 in)
Compression ratio	12.5 ± 0.5:1
Transmission	6 speed, multi-disk oil bath clutch
Frame type	Perimeter frame, Die-cast Aluminium spars w/ crossed reinforcement ribs Asymmetric aluminium swingarm
Suspension	Front: 40 mm inverted forks Rear: Progressive monoshock
Brakes	Front: Single 300 mm diameter stainless steel disc, radial 4-piston caliper w/ Bosch Single Channel ABS[3] Rear: 218 mm diameter stainless steel disc, single 30 mm piston caliper
Tires	Front: 100/80 - 17", Rear: 130/70 - 17"
Wheelbase	1353 mm
Dimensions	L: 1968 mm W: 760 mm H: 1135 mm
Seat height	820 mm (32 in)
Weight	129 kg[4] (dry) 144 kg (wet)
Fuel capacity	14.5 L (3.2 imp gal; 3.8 US gal) Reserve: 3.5 L (0.77 imp gal; 0.92 US gal)
Fuel consumption	2.71 L/100km
Related	Aprilia RS125, Aprilia RS4 50

Specifications

The powerplant is an electronically fuel-injected 4 stroke 4 valve DOHC single cylinder, with a balance shaft.^[6] A race kit is available from the manufacturer that boosts power from the standard 15 bhp to 25 bhp.^[5]

The RS4 125 is available with a quick-shift system similar to the RSV4, in which the engine halts the torque from the engine based on engine rpm, the amount of throttle being applied, and the speed of the bike. This system allows smooth, fast upshifts without the use of the clutch.^[5] This is optional on the standard bike, but included with the GP Replica model.

The chassis is a die-cast aluminium perimeter frame with an aluminium swingarm. The brakes consist of a 30 cm steel disc in front with a four-piston radial caliper, and a 22 cm steel disc with a single caliper at the rear. Complementing this for 2017 is Bosch 9.1ML single channel ABS, at the front.^[3]

For 2021, the RS125 has undergone significant changes: some restyling at the front, fully digital instruments, a wider 140-section rear tyre, Full-LED headlights, Euro 5 emission compliance and dual-channel (i.e. front and rear) ABS.^[7][8] The engine has also been modified: there is a new head, redesigned combustion chamber, new intake and exhaust ducts, redesigned camshafts and an iridium spark plug. The air intake and filter have been altered and the throttle body has been repositioned. There is a new exhaust system and catalyst, resulting in higher efficiency.^[9]

For 2025, the bike gains switcheable on/off traction control with an anti-rollover system, passes the Euro5+ emissions standard, and gets two new colours: Kingsnake White and Cyanide Yellow.^[10]