RX 250 4T

Displacement 249,8 cc
Bore 78 mm
weight 101 kg
Ground clearance 340 mm

SUSPENSION
KAYABA SUSPENSION:
MX2-SPECIFIC TUNING

The suspension system relies on the KYB front forks and rear shock, already successfully used on the 450, but here equipped with a specific setting developed to adapt to the character and masses of the compact 250 powerplant. Contributing to completing the chassis package is a targeted choice on the wheel front as well: the rear rim features a narrower cross-section compared to the other models in the range, with the precise objective of reducing rotating masses, increasing the overall agility of the vehicle, and limiting power losses when putting the horsepower to the ground.

ELECTRONICS
LAUNCH CONTROL AND QUICK SHIFT: RACE-READY TECHNOLOGY

The responsiveness of the new 250cc engine is supported by superior electronic management derived directly from the world of racing. The introduction of Launch Control, adjustable across five levels of intervention, optimises traction at the starting gate to maximise initial acceleration. The system works in synergy with the all-new Quick Shift, which allows higher gears to be engaged without closing the throttle or using the clutch, ensuring optimal gear-change smoothness and constant forward thrust.

DUAL INJECTION SYSTEM

To maximise engine performance, a sophisticated dual injection system has been introduced. This system features two dedicated injectors: one positioned on the throttle body and one installed directly in the airbox sleeve. This configuration allows for optimal management of the air-fuel mixture, significantly improving response at low revs and ensuring constant power delivery at high revs.

RECONFIGURED DOHC VALVETRAIN

The all-new 250cc engine features a DOHC timing system with overhead camshafts and a chain positioned on the right-hand side rather than the left, driven by a gear linked to the water pump shaft. The timing system uses a Morse-type chain, equipped with a hydraulic tensioner, to ensure maximum reliability even at the high revs delivered by this model.

ELECTRIC STARTER AND LITHIUM BATTERY

Reliable and secure starting on the first attempt in any weather or racing conditions, ensured by the standard electric starter powered by an ultra-lightweight lithium battery.

RACING CRANKSHAFT AND CONNECTING ROD

The internal architecture of the engine reflects the project’s pure racing DNA: the crankshaft features components made from dedicated forged steel and is supported by roller main bearings. The monobloc connecting rod utilises a bushing at the engine head to best withstand the specific high pressures, whilst the piston adopts a robust box-in-box structure.

HANDLEBAR CONTROL AND COMFORT

The handlebar of the RX 250 4T is isolated using silent block supports to effectively dampen high-frequency vibrations, reducing arm fatigue during longer riding sessions. For MY27, 5 mm raised handlebar supports have also been adopted to promote a more natural and effective riding position, combined with new grips featuring a softer compound.

DRY SUMMER SYSTEM

Unlike its bigger sister, the RX 250 4T’s lubrication system employs a dry sump circuit with dedicated return and delivery pumps. The system uses the same oil, suitably filtered, to lubricate both the engine and the transmission, an engineering choice designed to optimise space whilst ensuring total efficiency under load.

5-SPEED GEARBOX AND HYDRAULIC CLUTCH

The engine is mated to a 5-speed gearbox completely redesigned for this displacement, engineered with geometries and thicknesses that reduce weight and bulk without compromising the mechanical strength of the transmission. The clutch control relies on an updated hydraulic unit derived from the RX 450, capable of ensuring smooth and consistent operation race after race.

CFD-OPTIMISED COOLING

The engine’s thermal efficiency is ensured by a cooling system developed through in-depth computational fluid dynamics (CFD) analysis. This study enabled the optimisation of internal fluid flow and overall heat exchange, leading to the adoption on the RX 250 4T of a closed-type impeller that improves system efficiency and eliminates the need for external piping.

CHASSIS DESIGNED FOR THE MX2 CLASS

The frame has been entirely designed around the specific geometry and stresses of the new 250 4-stroke engine. It features a more tapered lower engine cradle section and dedicated side engine head connections. This configuration increases the vehicle’s overall torsional rigidity, whilst maintaining the optimal vertical flexibility required for intense motocross use.