1. Introduction
For 17YM Honda introduced an all-new, competition-ready Enduro machine into its off-road line up – the CRF450RX. And it took as its rock-solid base the engine and chassis of the 17YM CRF450R – Honda’s first totally new 450cc motocrosser in eight years – with modifications including larger fuel tank,18-inch rear wheel, revised PGM-FI mapping and suspension changes.
The CRF450R was the perfect platform to expand on and gave the CRF 450RX both the pure DNA to deal with any enduro stage and the confidence-inspiring competence to handle flat-out trails, challenging climbs and tight, tricky sections. And, just as importantly to an owner, it’s a high quality machine built with the long-term Honda reliability that makes it easy to live with over years of use.
Development has mirrored the CRF 450R, too. An HRC-developed cylinder head upped peak power and torque considerably in 19YM; HRC launch control was also added along with revised rigidity balance for the frame and swingarm, a new front brake caliper and adjustable-position Renthal Fatbar. For 20YM, just like its MX sibling, it received Honda Selectable Torque Control (HSTC).
21YM saw a major evolution for the CRF 450RX. Starting from the exact same point as CRF450R, almost totally redesigned by HRC. For 22YM, the CRF 400RX Enduro, sibling of the CRF 450RX gains an ECU remap and suspension updates further polishing a complete off-road package.
The 25YM CRF400RX is also, in turn, nearly all-new. It adds upgraded stability on rough terrain to its turning performance with increased throttle control of the engine. As ever it’s an off-road tool designed to make going faster easier – for longer.
2. Model Overview
Enhanced stability and control – over the roughest conditions – were goals for the 25YM CRF400RX. The aluminium twin-spar frame is 70% new, with a completely revised rigidity balance alongside new subframe attachment points, top/bottom yokes and stem, front wheel axle/clamp and Pro-Link ratio.
The Showa suspension has been completely remade and aims to deliver consistent damping and suspension reaction from bottom to top stroke. Both 49mm front fork and rear shock feature new settings; the shock is also now much easier to remove. HRC provided the blueprint for the new front brake caliper; it features new machining for the body, plus new pistons and seal grooves to resist heat fade over race distance.
For enhanced throttle control, drive and power past peak output the 4V Unicam engine employs a straighter path for airflow on the intake side, an extended exhaust downpipe and revised PGM-FI settings. The muffler meets new FIM noise regulations.
Crisply redesigned radiator shrouds specifically for enduro use, and CRF family graphics mark out the 25YM CRF400RX, alongside a Honda Wing on the front mudguard.
3. Key Features
3.1 Chassis
• 70% redesign of aluminium twin-spar frame improves overall stability
• New top/bottom yokes and front wheel axle clamp and spindle
• Brand new Showa front/rear suspension delivers smooth, consistent damping control
• Revised Pro-Link shock linkage structure and ratio
• New HRC-design front brake caliper resists heat fade
• RX spec. includes 7,7L fuel tank, 21/18inch front and rear wheel combination; aluminium sidestand and knuckle guards
The 25YM CRF400RX – well established as a fast-steering, lightweight tool – pushes handling ability further with increased straight line and cornering stability, bump absorption, and feel for front and rear grip.
The twin-spar aluminium main frame features a 70% redesign, with the aim of enhanced overall chassis stability on the roughest of track conditions. A redesigned front down tube, stiffener spars and side gusset stiffener combine with new pivot plates, upper shock mount and tension bracket to generate 8% more torsional rigidity improving stability. The torsional/lateral rigidity ratio is 5% greater, elevating cornering performance.
Vertical torsional rigidity increases 4%, suppressing deformation and high-speed instability; the rear subframe now mounts on the high-rigidity pivot plates (rather than the frame spars). This change reduces the transmission of energy (and subsequent movement) from the back of the machine to the rear head pipe section by 27%.
A great deal of work has gone into the top/bottom and steering stem to get a more consistent and stable suspension stroke. Alongside revised fork outer tubes and new front axle bolt the 25YM setup is more rigid, equalling a reduction of 6% in rigidity change during the stroke. The 585.2mm aluminium swingarm is unchanged.
Rake and trail are specific to the RX and set at 27°27’/116mm with 1,478mm wheelbase and 332mm ground clearance. Dry weight is 110kg with a 49.1/50.9% front/rear balance (wet).
Even more development has gone into the suspension. The aim has been to make fork stroke smoother, by removing any obstructions, while adding appropriate friction – 200% more friction force – throughout the entire stroke, with consistent damping force from top to bottom.
The Showa 49mm USD coil spring forks are effectively brand new with each component part – from outer rigidity to all internals – remade to deliver enhanced control from the initial movement all the way through. It employs a 310mm stroke and the oil specification is also new, to enhance low-speed damping. There are 16 adjustment positions for both of rebound and compression; all settings are unique for the RX and have been revised for 25YM.
Matching the forks the Showa rear shock has been remade to deliver consistent, uniform control anywhere in the stroke, with friction reduced in the bottom. There are 17 adjustment positions for rebound and 3.5 turns for high and 13 adjustment positions for low-speed compression, all revised for 25YM. A revised Pro-Link structure is 11% more rigid, with ratio curve/axle travel optimised to deliver smoother bump control.
The 25YM CRF400RX has also been designed to make shock removal/replacement quicker, with only four parts needing removal, cutting time in half.
Drawing from parts employed by HRC’s factory race bikes the re-machined, two piston front brake caliper uses new pistons and piston seal grooves. The new design reduces lever play by 57% when caliper temperature is high, while the caliper itself reduces rigidity change when hot by 25%, improving brake lever linearity and reducing rider fatigue. The 260mm wave-pattern disc is unchanged; a single-piston rear caliper is matched to a 240mm wave-pattern disc.
Knuckle guards protect hands and levers while the forged aluminium sidestand tucks away neatly to minimise interference while riding. DID aluminium rims, with directly attached spoke pattern layout are finished in black; the front is a 21 x 1.6in, the rear an 18 x 2.15in and mount Dunlop’s bespoke enduro-ready Metzeler Six Days Extreme.
Minimal bodywork aids rider movement around the machine. The radiator shrouds have been updated for 25YM specifically for enduro use, using the consistent CRF design philosophy focussed around lightweight/mass centralisation/ergonomics. A flat knee trajectory, front to back of the machine, has been maintained. New CRF family graphics denote the model change, and a Honda Wing makes an appearance on the front mudguard. The plastic fuel tank holds 7,7L. Radiators are protected by sturdy steel guards. The RedMoto redesigned plastic fuel tank holds 7,7L.
The full led headlight perfectly integrates with the streamlined CRF design. Sturdy back mudguard with integrated support for the registration plate, that also increases the resistance to the hits, typical of heavy off-road use.
Standard-fit, lightweight Renthal Fatbar flex for optimal comfort; the top yoke features two handlebar-holder locations for moving the handlebar rearward and forward by 26mm. When the holder is turned 180°, the handlebar can be moved an additional 10mm from the base position, resulting in four unique riding positions.
3.2 Engine
• More direct airflow intake route improves throttle feel in tight turns
• Extended exhaust downpipe builds mid-range range control
• Traction drive improved plus power up past peak output
• Efficient radiator cooling with fan
Improved throttle feel and torque in the mid-range and extra power past peak are the result of RedMoto’s development of the 25YM 412.6cc four-valve Unicam engine – to make getting out of a tight corner much quicker and easier, as well as driving 3rd gear harder, and for longer.
The airflow route – through intake, airbox, intake funnel and 44mm throttle body – is more direct than the previous design, reducing resistance and improving throttle control. In conjunction a new, extended header pipe builds more controllable character into the low- to mid-range zone. New settings (RX specific) for the PGM-FI match the engine’s new performance parameters. The exhaust muffler is constructed from heat-treated aluminium to better stand up to the rider’s boot and meets the new FIM 109dB noise regulation.
Bore and stroke are set at 92 x 62.1mm with compression ratio of 13:1. A gear position sensor allows the use of three specific ignition maps for 1st and 2nd, 3rd and 4th, and 5th. An 8-plate hydraulic clutch gives outstanding control and feel at the lever as well as delivering consistent lever clearance under arduous riding conditions. It also reduces slippage at peak output.
Rock-solid reliability has always been a big factor in the CRF400RX’s success and a 5-hole piston oil jet and dual 12mm drum scavenge pump manage all-important lubrication. The CRF 400RX is also equipped with cooling fan to maintain a constant temperature even on the slowest trail.
3.3 Electronics
• Honda Selectable Torque Control (HSTC) with 3 riding Modes (plus OFF)
• HRC Launch Control offers 3 start options
• Engine Mode Select Button (EMSB) features 3 maps to adjust output character
• HRC Setting tool tailors Aggressive and Smooth modes
The HSTC works to minimise rear wheel spin (thus reducing wasted forward drive) and maximise traction. It doesn’t use a wheel speed sensor, and critically maintains feel at the throttle while managing power; ignition timing is retarded and the PGM-FI controlled when the rate of change of rpm is detected to have gone over a set amount.
Three Modes differ in drive management level for different riding conditions:
Mode 1 intervenes most lightly, and after the longest time ¬– useful for reducing wheelspin
Mode 2 naturally offers a mid-point between 1 and 3 in terms of speed and strength of intervention and maintaining control in tight corners.
Mode 3 has the system intervene more quickly and strongly, and is therefore useful in more slippery, muddy conditions.
HSTC can also be switched off completely. When the engine is turned on, the system uses the last-selected setting.
The Launch Control also has 3 Modes: Mode 1 has a high rev limit, 2 (the factory setting) uses a middle point with 3 set low. There are 3 Modes available via the Engine Mode Select Button (EMSB) to alter engine character. Mode 1 is the factory setting, 2 smooth and 3 aggressive.
The Launch Control indicator, EFI warning, HSTC and EMSB mode button, and LED indicator are sited on the left handlebar. Pressing and holding the HSTC button for 0.5s will cycle the system to the next mode, with a green LED indication – 1 blink for Mode 1, 2 for Mode 2 and 3 for Mode 3 – to confirm selection.
