Now in its second generation, the CRF250RX is an excellent choice for professional closed-course off-road racers, with SLR Honda's Tallon LaFountaine having raced it to the 2021 AMA NGPC Pro II National Championship and the WORCS Pro 250 title. Also campaigned in GNCC and U.S. Sprint Enduro competition by Phoenix Racing Honda riders Cody Barnes and Ruy Barbosa, the model is based on the motocross-focused CRF250R, but tailored for woods racing, off-road grand prix competition, desert racing and trail riding in legal off-road areas, thanks to application-specific features that provide appropriate suspension performance, power delivery, fuel range, hand protection and convenience.
MODEL-SPECIFIC FEATURES
Compared to the CRF250R motocrosser, the CRF250RX has the following differences:
- A resin 2.1-gallon fuel tank (instead of the R model's 1.7-gallon titanium cell), providing enough range to compete in closed-course off-road competition.
- Both front and rear suspension have dedicated settings developed specifically for closed-course off-road application, for improved compliance over technical terrain like rocks and roots.
- The CRF250RX's ECU features a different fuel-injection map, with settings that deliver a smooth spread of power, maximizing traction in slippery, off-road conditions.
- Whereas the CRF250R has a 19-inch rear wheel, that of the CRF250RX is an 18-inch size, for a taller tire sidewall that better absorbs obstacles typically encountered off-road. In addition, front and rear tires are Dunlop Geomax AT81, which offer all-around performance plus high levels of ruggedness for off-road racing and riding.
- The CRF250RX comes standard with plastic hand guards, to help fend off trailside bushes and brush. It also has an aluminum side stand, which facilitates parking away from the pits but tucks out of the way when not in use.
ENGINE / DRIVETRAIN
The CRF250RX's 249cc liquid-cooled, single-cylinder, double-overhead camshaft four-valve engine design achieves excellent performance and durability. Low rpm torque is maximized through the design of the air intake, valve timing and exhaust port, but strong top-end power is also on tap.
Intake
The shape of the airbox results in a large capacity, particularly on the clean side of the air filter. The fuel injector's lean angle is 60 degrees, enabling the spray to reach all the way to the back of the butterfly, and the throttle bore is 44 mm. Together these features cool the intake charge, maximizing air-intake efficiency and torque at low revs. The air filter features a spring-loaded clip design for easy serviceability.
Head
The cylinder head features four titanium valves (33 mm intake and 26 mm exhaust), with the former using dual springs (one inside the other) to ensure precise movement at higher revs. The intake camshaft sprocket is press-fit, which enhances valve-timing accuracy while minimizing weight.
The camshaft holder has a rigid design that maintains camshaft-journal roundness, contributing to timing accuracy and minimizing friction at high rpm. Durability at high engine speeds is maximized by a high flow of lubrication to the oil-supply journal and the cylinder head. The bore and stroke are 79.0 mm and 50.9 mm, respectively, and the compression ratio is 13.9:1. The water-pump gear is thick to enhance strength.
Exhaust
The exhaust system utilizes a single straight exhaust port for good torque and low-rpm drivability. The single exhaust header is routed close to the engine on the right side for a narrow cross-section and good rider mobility, and the single muffler has internal baffling that is optimized for torque delivery.
Electronics
In order to fully realize the engine's performance potential, the ECU mapping supplies the optimum air/fuel mixture and ignition timing at all throttle positions and engine speeds. HRC-inspired launch control facilitates holeshots.
Clutch
The clutch pack has nine discs to maximize the amount of disc friction material and minimize the load on the individual discs. The clutch basket is rigid for durability, a friction spring reduces spring load, and lubrication is optimized to reduce wear. The primary ratio is 3.047, and lubrication is optimized to enhance clutch endurance.
Transmission
When designing the five-speed gearbox, engineers made efforts to enhance feel when making up- and downshifts between second and third gears—a very common operation on a 250 closed-course off-road bike. Only one shift fork is operated to execute this gear-change, the countershaft has good rigidity, and the shift drum is light thanks to a large through hole and use of only two lead grooves.
CHASSIS / SUSPENSION
The CRF250RX is known for delivering reliable tracking, precise turning, exemplary straight-line stability and overall rideability, and it has a low overall vehicle weight to facilitate increased maneuverability.
Wheelbase is 58.1 inches, rake is 27.32º, trail is 115 mm, the seat height is 37.8 inches, and ground clearance is 13.1 inches.
Frame / Subframe
The lightweight aluminum frame has widely curved main spars with small cross-sections, plus optimized rib placement in the backs of the pivot plates. Longitudinal rigidity is optimized for straight-line stability, while lateral rigidity is optimized to enhance handling feel when cornering.
The subframe features a simple design that doesn't require a separate seat support, to minimize weight.
Suspension
The coil-spring Showa fork is a 49 mm fully adjustable leading-axle, inverted telescopic design with 12.2 inches of stroke. The upper and lower triple clamps are designed with optimized reinforcement ribs, delivering flex for handling and feel through a corner. Traction and bump-impact performance are excellent as well, and the bike has an agile corner approach, with sharp handling characteristics.
The Pro-Link® rear-suspension system uses a Showa shock absorber with adjusters on the right side. Rear travel is 12.3 inches. An ultra-light steel shock spring is used, and the swingarm is narrow, providing clearance in ruts.
Wheels
The black D.I.D rims (21-inch front, 18-inch rear) deliver durable performance and good looks. Petal-style brake rotors (260 mm front, 240 mm rear) disperse heat.
The CRF250RX comes with Dunlop Geomax AT81 tires, which offer excellent all-around performance plus high levels of ruggedness for off-road racing.
DESIGN
Rider-active design is a key feature of the CRF250R. The cross section is narrow in the middle and at the rear, the seat has a flat layout, and the radiator shroud-side panel junction is smooth. These user-friendly ergonomics permit the rider to easily adjust body position when cornering, accelerating, jumping and braking.
Cooling the CRF250R engine is crucial to maintaining performance and overall durability. Computational Fluid Dynamics (CFD) were used to design air-outlet vents in the shrouds, and the radiator grills optimize the number of fins, as well as their angle. Each radiator shroud is produced in a single piece instead of two separate parts.
The seat base has rearward-facing tongues and front-located mounting tabs, an arrangement that eases installation, and acceleration forces keep the seat securely in place. The 1.7-gallon fuel tank is made of lightweight titanium.
Only eight fasteners are used to secure all of the main bodywork components – both radiator shrouds, both side plates and the seat – and all of the bolts for the main bodywork parts have 8 mm heads, simplifying maintenance.
The Renthal® Fatbar® handlebar is held by a clamp that can be turned 180º; because the clamp itself has two mounting locations, there are four possible mounting positions for the handlebar, through a range of 26 mm.
