A Step-By-Step Guide To A Friendlier Honda CRF450RX
When Honda debuted the CRF450RX for model year 2017, we hailed it as a potent off-road racing weapon, with a motor, gearing, and power delivery quite similar to its motocross sibling.
The acceleration was ferocious, especially in the aggressive mapping mode, and the suspension settings and spring rates were a bit on the stiff side for off-road competition, thought ideal for a vet-style motocross track.
The 2018 Honda CRF450RX is essentially the same bike as the previous year, however Honda opted to reduce a little weight by dropping the kickstart lever and swapping the old lead-acid battery out for a lightweight lithium-ion unit. Additionally, the ECU mappings and suspension valving have been optimized to increase rider “usability”.
With the 2018 Honda CRF450RX providing such a capable platform, we were excited for the opportunity to conduct a long-term test. Given the luxury of time, our project objective is to formulate the setups, seek out the upgrades, and discover the hacks to really create the ultimate do-anything dirt bike.
Part 1: Create a Baseline
Engine hours: 0 – 4.2
The Honda CRF450RX is a closed-course competition machine and, before we install the necessary exhaust items to put us on the right side of the law, we need to create a baseline for measurement and evaluation in completely stock trim. That’s when it helps to have friends with private property with all of the fixings, including an MX track, GNCC-style off-road loop, and a turn track that is great for fork settings.
Before I was halfway through the one-mile off-road loop, I could already appreciate the ECU and suspension valving changes that were made for 2018. Overall, the ferocious power delivery was smoother and less abrupt, allowing us to use both the Traction (1) and Standard (2) ECU mappings with great affect. To our delight, gone is the mid-range flat spot on the Traction (1) setting from the previous year.
On the suspension side, the fork seems to work better with a full tank of fuel than the 2017 version and the first-third of travel is more compliant over braking bumps. Contrary to the feel of last year’s bike, it’s not as necessary to slide your weight all the way to the gas cap to get the front end to bite.
Of course, the overall handling is Honda-sharp. We were quickly reminded of the stiff, yet precise feedback we got from the 2017 model, compliments of the aluminum frame and Renthal crossbar handlebar combination.
This is definitely an area of rider preference, and we like this feel for MX, but prefer a more flexible feel to reduce fatigue in longer format off-road race events. We’ll give this some time and additional evaluation before making any changes in this area.
Bottom Line: The 2018 CRF450RX rips! The small reduction in weight and tweaks to the ECU mappings and suspension valving work great are all welcome changes. Let’s go racing!
Part 2: Break-In Oil Change
Engine hours: 4.2
The recommended service interval from Honda for changing the oil and oil filter is 15 hours. That’s twice as long as the Yamaha YZ450FX and 50 percent longer than the KTM 450 XC-F. To further put things in perspective, Honda also recommends that the piston and rings be changed out every 15 hours.
My approach is to change the oil and oil filter more often, so hopefully I can change out pistons and rings and less frequently. I’ve had good luck with this approach, but you ignore recommended service intervals at your own risk.
In the end, even the best oil is cheap insurance against engine failure. We use Bel-Ray Thumper Racing Full Synthetic Ester 10w-50 and have never had an engine wear issue. It will set you back about $16 a quart, and we think it’s worth every penny.
The entire oil change process on the CRF450RX is straightforward. Warm it up, remove the plastic skid-plate to access the oil drain plug, and let the old oil flow into a pan. Normally we hold the kill-button and turn over the engine a couple of times with the kickstarter to ensure we drain the entire cavity, but without a kickstart lever on the 2018 machine, a quick stab at the starter button accomplishes the same feat. With only one oil cavity to drain, and easy access to the filter, the entire process takes less than 10 minutes.
Examining the old oil through a translucent Ratio Rite measuring cup, it looks completely spent after a break-in period and 4.2 hours of flogging at the private test track. There’s no doubt that the monstrous horsepower from the CRF450RX puts a lot of strain on the clutch plates, as evidenced by the dark maple syrup look of the oil.
Part 3: Legalize It
Engine hours: 6.8
As much as I love riding at my buddy’s private place, it requires a lot of coordination and drive time, so we have to make our trusty CRF450RX legal for riding in the National Forests and the California State Vehicular Recreation Areas.
The dual exhaust setup of the Honda can represent a financial challenge when it comes to investing in spark arrestors. The truly budget-minded could switch to a single exhaust muffler system, but undoubtedly would experience a performance loss. Still, there are exhaust manufacturers that offer a single exhaust on the right and include an aftermarket side-plate for the left without the flare to hide the fact that a muffler is missing. Not ideal, and why invest in a new bike if you’re going to make it look old.
We contacted the performance gods at Yoshimura R&D and they set us up with their Signature RS-9T dual stainless-steel exhaust system with carbon fiber endcaps. These include USFS-approved screen inserts for legal compliance.
Although they are about the same weight as the stock aluminum mufflers, the Yosh RS-9T exhaust cans have increased volume and a larger core and claim to improve throttle response and provide mid and top-end gains. The Yosh team design and tested the RS-9T system in conjunction with HRC engineers, so the fit and finish is nothing less than Factory spec.
Once fired up, the exhaust notes at idle are crisp and throaty, and a twist of the throttle actually delivers a bark a bit quieter and less raspy than the stock exhaust setup, which is a very good thing on public or private lands.
The Yoshimura RS-9T setup looks incredible, installation is a breeze, and a quick late afternoon spin on the practice track showed that the performance is there. Now we’re legal!
Bottom Line: The Yosh RS-9T setup is the real deal. Don’t sacrifice performance or aesthetics to comply with Johnny Law.
Part 4: To the Forest we Go!
Engine hours: 12.8
Now that we have our super-trick Yosh RS-9T exhausts installed along with the all-important spark arrestor inserts, we’re ready to rail the public trail system. Well, almost. Handguards are pretty essential, and we prefer the all-plastic wraparound type for two reasons.
An all-plastic design allows for the bars to flex, and with the stiff feel at the grips that the CRF450RX has, we need all the flex we can get. Also, the wraparound design helps to save levers in the event of a tipover, which can make all the difference in race conditions.
Given the close-ratio motocross transmission, fast and flowing trails are where the CRF450RX really excels. First gear is a little too tall for technical goat trails, and fifth gear isn’t tall enough for 80+ mph desert valley crossings. That said, with a 50-tooth rear sprocket, the RX is geared perfectly for everything in-between. Of course, if we had our druthers we would opt for wide ratio gearbox and/or a sixth cog, but we’re having too much fun to dwell on that for now.
Out on the trail, the Yosh exhaust has totally proven that its performance matches its stellar looks. Even with the spark arrestors installed, it feels like we’ve gained tractability without losing any top end power. Any remnants of a flat spot on the Traction (1) ECU map is completely gone. We couldn’t be happier.
As we’ve mentioned before, the stock suspension settings feel better than the 2017, especially the fork. For off-road racing, we like to optimize suspension setting to keep the bike balanced through whoops, and for all of your west coast racers, you know that’s about 90 percent of the terrain!
We tested out different settings with the rear shock, and settled pretty close to stock, with high speed compression damping at three full turns out, and low-speed compression and rebound at six- and 13-clicks out respectively.
The fork works well right out of the box. Depending on conditions and traction, we’ll go back and forth a couple of clicks on the compression and rebound as needed. Less damping in hard pack and slick conditions and a little more when traction is more abundant.
When the trail deteriorates to Endurocross-like conditions, the tall first gear coupled with a very light flywheel feel results in more than the usual amount of engine stalling. Revving up the motor to avoid flaming out the engine puts undue stress on the clutch, so we’re going to look at possible solutions for our next installment.
Bottom Line: The CRF450RX absolutely rails fast and flowing trails, with a motor, gearbox, and suspension optimized for race-pace trail riding.
Part 5: Oil, filter, and tires
Engine hours: 12.8
We’re a little over eight hours of motor time since our last oil change, so it’s time for another 1040cc of Bel-Ray Thumper Full-Synthetic Ester 10w-50 and a Honda OEM filter. Even with the abuse we’ve put on the clutch, the oil looks much better than the initial break-in oil change, which I attribute 100 percent to the Bel-Ray oil. I think we’ll stretch out the interval to 10 hours next go ’round.
It’s also time for some new rubber as well, though the stock Dunlop Geomax AT81 tires has proven to hold up extremely well. When the AT81s are new, the grip is fantastic, even on hard-pack blue-grooved clay. Even more impressively, once they wear after the first hard ride, they really kind of stabilize at about 85 percent of full grip and just stay there for an extended period of time—a great bang for the buck.
Bottom Line: We like riding more than wrenching, so longevity is key. Two thumbs up for Dunlop Geomax AT81 and Bel-Ray Thumper Full-Synthetic Ester!