The Aprilia RS4 125 (sold as the RS125 since 2016) is a ''125 cc'' class

sportbike A sport bike (sports motorcycle, or sports bike) is a motorcycle designed and optimized for speed, acceleration, braking, and cornering on asphalt concrete race tracks and roads. They are mainly designed for performance at the expense of comfo ...

manufactured by Italian motorcycle firm

Aprilia Aprilia is an Italian motorcycle manufacturer founded immediately after World War II in Noale, Italy, by Alberto Beggio. The company started as a manufacturer of bicycles and moved on to manufacture scooters and small-capacity motorcycles. ...

. 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 The Derbi GPR 125 is a street motorcycle sold by Derbi - Nacional Motor since 2005. The original GPR125 was powered by a single-cylinder two-stroke engine with a steel lined cast iron cylinder manufactured by Yamaha, but was superseded in 2010 by ...

Specifications

The powerplant is an electronically fuel-injected 4 stroke 4 valve

DOHC An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion c ...

single cylinder, with a

balance shaft Balance shafts are used in piston engines to reduce vibration by cancelling out unbalanced dynamic forces. The counter balance shafts have eccentric weights and rotate in opposite direction to each other, which generates a net vertical force. Th ...

. A race kit is available from the manufacturer that boosts power from the standard 15 bhp to 25 bhp. 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. This is optional on the standard bike, but included with the GP Replica model. The chassis is an 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. 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 ABS. 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.

Notes and references

{{Aprilia motorcycles RS4 125 Sport bikes Motorcycles introduced in 2011