2019 Factory Off-Road Bikes—Trevor Stewart’s Honda CRF450RX

Inside the two-time National Grand Prix champ’s rocket.

Parked in front of the JCR Honda workshop with an HRC Honda CRF450 Rally among the bikes in the background, Trevor Stewart’s JCR Honda CRF450RX is a championship-caliber machine thanks to his talent, carefully chosen modifications, and painstaking preparation.
Parked in front of the JCR Honda workshop with an HRC Honda CRF450 Rally among the bikes in the background, Trevor Stewart’s JCR Honda CRF450RX is a championship-caliber machine thanks to his talent, carefully chosen modifications, and painstaking preparation.Mark Kariya

Grand prix-style racing out west carries some unique requirements. Usually based at a motocross track, the courses add off-road elements which can impose tight, technical terrain as well as tapped in top gear sections. And with more than 1,000 entries the norm for a race weekend, the courses tend to get very, very rough at the end of the day, which is when the pros race for 90 unforgiving minutes.

Thus, while GPs are often considered fast, long motocross races, they can also include enduro-tight/EnduroCross-technical sections as well, making them more diverse than the average MX track.

Trevor Stewart won both the 2018 and 2019 GP titles, the latest one carrying full AMA National status as the FMF AMA National Grand Prix Championship (NGPC) Series, and he did it on Johnny Campbell Racing (JCR) Honda CRF450RXs.

The JCR crew feels suspension is one of the most important systems on the bike and tasks Pro Circuit to give Stewart the stiffer, more controlled action at both ends with Showa A-Kit parts enhancing the front. Maxxis tires with Nitro Mousse foam inserts plus Galfer’s brake systems are also common at both ends with an Acerbis carbon fiber guard protecting the front rotor.
The JCR crew feels suspension is one of the most important systems on the bike and tasks Pro Circuit to give Stewart the stiffer, more controlled action at both ends with Showa A-Kit parts enhancing the front. Maxxis tires with Nitro Mousse foam inserts plus Galfer’s brake systems are also common at both ends with an Acerbis carbon fiber guard protecting the front rotor.Mark Kariya

There’s not a lot of difference between the 2018 and 2019 models, so it made it somewhat easier for the JCR Honda team to set up the latest version. Lead mechanic Gage Day filled us in on all of those modifications and began by confirming, “There actually wasn’t too much of a change from the ’18 to ’19 models. Honda changed the frame a little bit, a chassis upgrade. It’s pretty much similar to the setup of the ’18 that [Trevor] ran on the ’19,” lead JCR technician Gage Day begins. “He felt pretty comfortable with it. Obviously, with the new chassis and stuff there’s a couple tweaks, but if anything, we pretty much just addressed the suspension a little bit—just a couple little suspension tweaks here and there.”

Starting with the Showa suspension, JCR sends the fork and shock to Pro Circuit to let their techs massage both ends with stiffer springs and corresponding valving. In addition, Pro Circuit’s billet pull rods replace the stock pieces; while there’s not a huge difference dimensionally, Day says of the PC pieces: “I don’t think it was even a full millimeter [difference], but it changes the geometry of everything [in the rear suspension]. If you change a [millimeter] in the link, it could set the rear end a whole four to five mils lower depending on which way you go with it. We ran a little bit longer link just to make him happy with the rear end, but other than that it wasn’t a whole lot of changes.”

Although Day wasn’t sure of the exact settings Pro Circuit came up with, he knew they weren’t far off from the ones used on the ’18 bike, though he did concede, “As far as the setting from stock, it’s much stiffer. These guys are going so much faster than what the stock suspension setting can handle. You can adjust the stock suspension—it’s really good right out of the box—but the speeds these guys are going, it’s set up a little bit different, a little stiffer everywhere.”

The engine doesn’t require much power enhancement beyond the full Pro Circuit titanium exhaust system, VP race fuel, and JCR’s ECU mapping. A Hinson clutch and clutch cover replace the stock items for greater durability. Note the billet Pro Circuit pullrods, used to provide slightly more stability.
The engine doesn’t require much power enhancement beyond the full Pro Circuit titanium exhaust system, VP race fuel, and JCR’s ECU mapping. A Hinson clutch and clutch cover replace the stock items for greater durability. Note the billet Pro Circuit pullrods, used to provide slightly more stability.Mark Kariya

They like to run 103 to 104mm of sag.

In the engine bay, the crew feels that the engine in standard configuration is more than strong enough for Stewart’s needs. Most attention goes to broadening the delivery. They start with Pro Circuit’s Ti-6 Pro full titanium system, Day noting, “It just changes the power a little bit—gives it a little more power, but it broadens the spectrum of the power as well.”

He continues, “In addition, Pro Circuit alters all of our head porting, our head work. It’s nothing too drastic; it’s just more of a cleanup. The Honda 450RX comes with so much power in stock form, we’re not trying to go for more power. There’s so much power with these bikes that the racing we do—especially in the tighter, technical races—you don’t need a bunch of horsepower. Horsepower and speed don’t necessarily go hand in hand all the time. We’re just trying to make the power easier for some of the races.

“With that we ran the VP T4 fuel as well and some JCR ECU settings. [Those are designed] to go with the fuel and the exhaust system and the little bit of head work. It’s the same thing—we’re just trying to make everything [work well] together. There are so many different variations you can do with ECU settings. You could sit and test with that all year, but we had a pretty good idea from prior seasons of what works and what doesn’t really work with the products that we run, so we had a pretty good base to go off of.”

While the CRF450RX features a handlebar-mounted switch that allows the rider to choose from three different maps, one of those maps is not changeable so JCR’s mods are targeted to the two that can be modified.

“He pretty much just runs it in the most aggressive map that we came up with to our spec,” Day reveals.

Gearing is usually taller than standard, though it depends on that weekend’s course character. They swap the standard 13-tooth countershaft sprocket for a 14, then run anywhere from a 49- to 51-tooth Renthal rear, linked by D.I.D’s ERV3 sealed X-ring chain.

D.I.D’s black DirtStar ST-X rims are a bit sturdier than the stock hoops, but JCR retains the standard hubs and spokes. Gearing is a little taller than stock as well with a 14-tooth front and the rear Renthal varying between 49–51 teeth depending on the course. JCR also depends on a D.I.D X-ring chain.
D.I.D’s black DirtStar ST-X rims are a bit sturdier than the stock hoops, but JCR retains the standard hubs and spokes. Gearing is a little taller than stock as well with a 14-tooth front and the rear Renthal varying between 49–51 teeth depending on the course. JCR also depends on a D.I.D X-ring chain.Mark Kariya

While JCR retains the stock Honda hubs and spokes, D.I.D’s black DirtStar ST-X rims (18- and 21-inch) replace the standard items in the interest of added ruggedness. Maxxis tires grace both wheels, with Day noting, “We pretty much ran the SI tires all year long. We switched up the front for a couple rounds here and there just to try it out and it would be the MXST, the new Jeremy McGrath-inspired motocross front tire. I believe some of the other teams are using that [also], but we were pretty much tried and true with the Maxxis SI [front and rear].”

To avoid flats, they stuff the tires with Nitro Mousse’s latest Platinum-series foam inserts.

A 2.4-gallon IMS tank with quick-fill receiver is a must for long races. Renthal’s 999 Twinwall handlebar sits atop a BRP triple clamp with a Scotts steering damper reducing twitchiness at speed.
A 2.4-gallon IMS tank with quick-fill receiver is a must for long races. Renthal’s 999 Twinwall handlebar sits atop a BRP triple clamp with a Scotts steering damper reducing twitchiness at speed.Mark Kariya

A Twin Air filter makes sure the EFI gets nothing but clean air. Honda Pro Lubricants are used for all aspects of the RX except for what goes into the radiator; that job is entrusted to Evans coolants.

“We do not run bigger radiators,” Day declares. “The only kind of radiator modification I do to the bike is I extend the radiator louvers. I actually make an extension for the bottom of [them] to cover the radiator tank [on each side], then we’ll run the open mesh over the [radiator cores] to keep rocks out and keep the radiators clear for airflow as possible.”

Day adds, “We do not run any [radiator] braces; we try to keep the chassis as free as possible.”

Throttle Jockey is a longtime JCR sponsor, supplying both the graphics and seat. IMS Core pegs, Twin Air filter, BRP chain block, and Acerbis plastic skid plate are also used on the champ’s bike.
Throttle Jockey is a longtime JCR sponsor, supplying both the graphics and seat. IMS Core pegs, Twin Air filter, BRP chain block, and Acerbis plastic skid plate are also used on the champ’s bike.Mark Kariya

Longtime team sponsor Throttle Jockey provides both the graphics and the seat cover, which is used with the stock foam and seat base. Renthal’s 999 Twinwall handlebar sits above a BRP top triple clamp with a Scotts steering stabilizer helping keep the bike in line through the rough at speed. “We tried a couple different bends, but that was the go-to for him,” Day remembers.

Stewart hangs on via soft-compound A’ME half-waffle grips with other controls being a Motion Pro throttle tube, stock Honda front brake lever, and Works Connection clutch lever assembly. IMS Core pegs with their extra-sharp teeth grip Stewart’s feet securely. Day points out, “Trevor pretty much runs everything in a very neutral position—levers neutral, handlebar neutral. Nothing’s crazy with the setup.”

To ward off potential damage that off-road races dish out, Acerbis provides its plastics, including the hand guards and skid plate as well as X-Brake carbon fiber front brake rotor guard. An aluminum Zip-Ty Racing sharkfin guards the rear rotor, while BRP’s polymer chain block keeps that D.I.D running true. JCR uses complete Galfer braking systems front and rear—rotors, pads, and brake lines.

While their races don’t require quick wheel changes, one trick held over from JCR’s Baja days is the chain-adjuster block on the right (brake) side is fixed in place so it doesn’t fall out of the swingarm during one of those rare mid-race wheel changes.

Since Stewart’s races are up to two hours, a larger fuel tank is a must and IMS provides one in its 2.4-gallon translucent cell with quick-fill receptacle since a 450 in a fast race is fairly thirsty, EFI or not.

In a surprise move, Stewart recently announced that he and JCR would be parting company amicably, so he’ll be putting the number 1 plate on another bike this season. As this was written, neither party had announced any plans, though with the first race of the season in a few days, we may not know until that first pro race.