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Smart Mods To Improve The 2017 Honda CRF450RX

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This article was originally published in the October 2017 issue of Dirt Rider.

Honda’s 2018 CRF450RX is a completely new motorcycle, so there was certainly a lot to learn about it. In the 30 hours I’ve put on the bike, I’ve found some areas that needed fixing for me and saw what first the stock adjustments, and then what Pro Circuit, could do to help.

The previous-generation CRF450R 2009–2016 engine was good, but some people seemed to think it was a little slow. This new generation of engine is certainly not slow. Actually, the RX’s power is almost too responsive, to the point it can be a bit of a handful at times. This is the same engine and transmission as the 450R model with just one-tooth-bigger (50T) rear sprocket; the bike has a very noticeable on/off jerky feeling with a throttle that can be good for motocross but not as good on tighter single-track. The bar-mounted map selector’s three settings (1 being standard, 2 softer/traction, and 3 aggressive) do make a noticeable difference; after riding the bike only a few hours I settled on the second map.

We only had a few options when we went looking for an exhaust. Pro Circuit had just completed its new dual exhaust system for the 450RX and offered to let us test one of its complete systems. The Pro Circuit guys gave us a stainless-steel exhaust that is a tad bit heavier than stock but offers great performance and durability. Fitment was spot-on and installation was easy. I immediately noticed two things: The power was much broader and the bike was noticeably quieter. The Pro Circuit mufflers feature removable spark arrestors, which we left in (the OEM mufflers do not have spark arrestors, as this is a competition off-road model, not a green-sticker bike). Leaving the spark arrestors in helped make the bike quieter and made the power much more usable, and that’s what we were going for in the first place. Unless you plan on only riding this bike at a track I would recommend leaving the spark arrestors in.

I found myself almost never using first gear. The 450RX has the same close-ratio gearbox as the 450R, and I feel like the RX would benefit from a wider-ratio gearbox. Since that was not an option for us to change, I opted for a smaller rear sprocket. Simply going down to a 49-tooth rear sprocket allowed me to use first gear a little more and made second very good.

The 450RX is not exactly a featherweight; however, under normal conditions it does not feel overly heavy. Honda has long been working on a “center mass” principle to try to get the most amount of weight to the middle of the bike just below the rider. The more I rode this bike the more I started to feel like maybe big red has gone too far in this direction. After spending some time tuning the engine there was still a very noticeable teeter-totter feeling with the on/off throttle position. It’s not that there is an unusual amount of engine-braking; it’s more like all of the weight is too centered. The simplest way I found to help reduce this sensation was to just turn the idle up a little.

Now that we had tuned in the engine and power delivery I wanted to start working on the chassis, which is even more important than the motor.

I rode the bike at several different locations, including open desert, tighter single-track, and a few motocross tracks before starting to make any changes. The bike seemed to be more at home on a motocross track than off road or trails. The chassis has a light feeling that is easy to turn, and it loves to climb hills. The light and nimble feeling is good on lower-speed tight sections, but the opposite is true for faster sections and steep downhills. At medium speeds I struggled with the front-wheel traction quite a bit, mainly not being able to steer the bike where I wanted it. At higher speeds there can be some headshake if you are not completely committed to acceleration or heavy braking. I also noticed the bike seems to handle better with a full tank of gas versus a near-empty one. But the stock bike’s biggest weakness is fast, steep downhills; this is where the chassis was at its worst. And overall, it’s somewhat of an unbalanced bike.

There was no doubt the suspension was much softer than the 450R’s—it was especially noticeable on the motocross track—and I felt that was holding the bike back a little. Yes, I know this is an off-road bike, but I rode it everywhere to help find its strengths and weaknesses. Keep in mind Honda built this bike to be a competition model for racing GNCC, WORCS, Hare Scramble, and even motocross events for the right rider.

So next up to tune was the suspension. The fork and shock are Showa, same as the 450R, but with off-road valving and a softer shock spring. I started by stiffening the adjusters on the rear shock—going from 3-1/4 out on the high-speed compression to 1-1/2, and from 14 to 10 clicks out on low speed. This helped hold the rear of the bike up, with the goal being to transfer more weight to the front wheel. I also worked with the shock’s rebound adjuster; however, going only two clicks slower began to make the shock feel harsh. I stiffened up the fork three clicks also to help reduce bottoming on bigger hits. The bike began to handle better but lost some comfort in the rocks, as well as made the front and rear deflect and become a little difficult to keep under you.

After several rides and quite a bit of clicker adjusting I felt like I had hit a dead end. I knew the bike had more potential, but not being sure what direction to go next I decided to get help. Since Pro Circuit had already been testing with the JCR racing guys I figured it would have some good settings for this bike. Its guys gave the bike a full revalve, along with a stiffer shock spring, going from a 5.3 to 5.5 (5.5 is standard on the 450R model), and put on their shock linkage pull rods.

Since we were making a few suspension upgrades I opted to get a little more aggressive with the tires. I put on Dunlop’s MX3S front and the new MX3S 18-inch rear (stock are Dunlop AT81 tires).

Naturally, my first impression was, “Way better.” With the new shock settings and stiffer spring the bike felt a little stinkbug at first, even with 108mm of sag. Pro Circuit suggested closing the rebound a little on the shock. After a few rides and closing the rebound to nine the bike felt fairly balanced. Front-wheel steering was improved, as I feel the stiffer shock spring does help transfer more weight to the front. Bottoming resistance was way better, and the bike could be pushed much harder into obstacles. The downhill handling was also improved but still not to the point where I would say this bike likes to charge down steep hills. One area that might have gotten a little worse was flat, rocky sections; but this was not surprising after stiffening up the valving and shock spring.

I would like to see someone make a heavier flywheel for this bike. I feel like that would improve the power delivery and also the handling. The overall engine characteristic is that of a light flywheel; typically a heavier flywheel can help with rear-wheel traction and a more torquey power character. As for the chassis, a heavier flywheel could make the bike feel more predictable with less of the unbalanced, teeter-totter feeling.

This is a racebike, not a trailbike. If you want a bike you can ride at the track and not have to swap the tank or rear wheel to go trail riding, then this bike might be for you. If you are below an advanced B-level rider, this bike is probably too aggressive to be your off-road machine. If you are a top B-level or better rider, you might like this bike. If you are pro-level racer, you might really like this bike. It rewards those with very good riding technique with its quick and responsive handling.