2005 Honda CRF450X Development

1/19/2005 3:16:35 PM

CRF450X Development

Common sense seems to dictate that when something works, you stick with it. Following that thread of logic, if you already build the best motocross bike in the world, you could then create the world's best off-road machine by sticking with that base bike and adding a few tidbits. Simply install a bigger generator to power a lighting system and add flywheel weight, slip in a set of wider gearbox ratios, and call it a day.

While some manufacturers take this path, Honda does not. At Honda, commonplace solutions never override the quest for excellence. And because off-road competition differs drastically from closed-course motocross racing in myriad ways, machines for each purpose really should be developed autonomously to satisfy their decidedly differing parameters. All of which explains why virtually every single component on Honda's stellar CRF450R motocrosser has been changed to meet the unique demands placed on the CRF450X off-road machine.

When Honda engineers designed the four-stroke CRF450R motocrosser, they built it with the single-minded purpose of creating the best race machine in the world. By most measures - racing results, magazine comparisons, etc. - they succeeded. The world of off-road competition, however, demands an entirely different skills set, if you will. Sporting an ability to devour triple jumps, blast big bermshots and handle everything in between, a motocross bike would seemingly be ready to tackle anything the dirt has to offer. But once you've experienced the snaking pursuit of a GNCC course, the full-throttle-blasts of WFO speed in wide-open desert races and the mud-slinging slogging through endless stands of trees common to enduro events, you understand that the far-ranging requirements for off-road work have little to do with what a motocross or Supercross track demands.

Of course, to transform a championship-caliber motocross machine into a world-class off-road bike, Honda's engineers began at an enviable starting point: the CRF450R. Although both 450s share the same essential engine architecture and basic chassis design, virtually every piece on the CRF-X has been redesigned in the process, with the expressed intent of reaching the apex of performance in off-road function.

Same face, all new parts

Far from a Honda 450 motocrosser with lights, the CRF450X's list of altered parts runs from large to small, with plenty of changes in between. Just a highlight of the major changes includes:

- New cylinder head and valves to improve intake velocity and engine response
- New cam for a wider torque spread and increased low-end and midrange punch
- Wide-ratio gearbox for more versatility in varying terrain
- Added flywheel weight for more tractable power delivery
- New exhaust system complete with spark arrestor for added torque
- Larger fuel tank for greater range
- Electric starter, battery and high-output ACG - plus a backup kickstarter
- Completely new frame carefully tuned for off-road use, not motocross tracks
- More compliant suspension components for a plush ride over rocks and roots
- Revised linkage ratios for the Pro-Link rear suspension system
- An 18-inch rear wheel and tire for added flat-tire resistance
- A new lightweight slim-line headlight, plus a trick LED taillight
- Standard-issue sidestand with a clever mounting system integrated into the left footpeg bracket
- Both CARB and EPA certification in stock trim

Considering this is just the brief list, the CRF450X obviously incorporates substantial changes indeed. And while this list represents some of the nuts-and-bolts changes, the CRF450X's development involves an equally complex human tale.

Hands-on experience counts

When Honda's product development team set out to transform the 450R into the 450X with an entirely new off-road personality, the pursuit was neither academic nor theoretical. The process involved countless hours of hands-on testing by Honda's product development specialists. Feedback traveled back and forth from tester to engine and chassis engineers, resulting in new hardware that required more testing, more feedback. And that circle of development/testing goes on and on and on.

As one engineer explained, "For a while there, the testing procedure for the CRF450X seemed like a never-ending process. A number of times in a month, for a period of about 10 months straight, we tested new variations of chassis and engine alterations. Sometimes we tested in America, sometimes in Japan. And we had to test the bike in all kinds of terrain, all across the United States: sand, desert, woods, rocks, mud, tight trails - the whole works."

And even though this group had earlier worked on crafting the CRF250X off-road bike starting with the CRF250R motocross machine, the CRF450X proved to be a completely different animal at times. "In some ways it was easy to engineer the CRF450X, because the 450R is such a wonderful motocross bike," the engineer said. "In addition, we had a lot of solid data we gathered with our hands-on experience working with the CRF250X. However, many times the changes did not translate directly; we had to find new answers. But our previous experience had at least given us a process we could pursue during development of the 450X."

Key goals for the engine focused on maintaining the CRF450's class-leading performance, while retuning the engine to shift the power peak downward a bit in the powerband - all the better to focus on midrange punch, that most usable of real-world assets when riding off-road. Additional flywheel effect and a new wide-ratio five-speed gearbox increase the versatility of the 450X, and the addition of an electric starter commanded high priority. But complex as this may sound, chassis development proved even tougher yet.

Handling the bigger picture

Given the nature and scope of off-road riding, the very core of the CRF450X's aluminum frame and suspension had to offer more bump absorption and a plusher action than is common to motocross machines. Typically, off-road riders must deal with nonstop small-to-medium-sized irregularities in the trail, such as rocks, roots, bumps, dips and more, obstacles that jump up at weird angles and at the most inconvenient times and places. A bike designed for motocross will transmit too much bump impact under such conditions, often resulting in front wheel deflection that can wear out the rider in short order. A more supple and compliant package - suspension components and frame - is the order of the day for top off-road performance, and that's exactly what the CRF450X delivers. But a deeply complex picture lies beneath that simple explanation.

" We wanted to keep a lot of the CRF450R flavor, if you will," said one product development team member. "The 450R is a great bike, but the chassis is too rigid for optimum off-road use. So we made changes to the frame and suspension that would make the entire CRF450X package more compliant feeling, but we still had to maintain its high-speed stability, tracking ability and steering precision. It's all a delicate balance, but we found that sweet spot."

As explained in detail in the CRF450R technology section, virtually every single piece that makes up the 450X frame was re-engineered. In addition, the entire suspension system, including the fork, shock and linkage ratio on the Pro-Link rear end, has been recalibrated to produce a more compliant, plush ride specifically suited to the rigors of off-road use. All in all, the X-model chassis transformation required a monumental effort - but one that yields monumental results.

An engine brand-new through and through

Even though the CRF's 449cc engine offers a wealth of power, Honda once again re-engineered the entire powerplant - not to make more power, but to create a spread of power better suited to off-road use, and to also add conveniences and durability for use over repeated long-distance events. The X-version of the 450 engine retains the basic architecture of Honda's innovative Unicam four-valve powerplant. The overall engine layout remains unchanged, but the 450X incorporates intake and exhaust valves 1.0mm smaller in diameter to increase intake charge velocity and thereby improve throttle response. Many familiar key Honda innovations remain, such as the high-tech forged 96mm slipper-type piston with a compression ratio of 12.0:1, Nikasil® cylinder liner, and 40mm flat-slide carburetor.

However, the addition of a much-desired electric starter dictated the creation of all-new engine cases, and the cylinder, head and camshaft are new pieces as well, even though they mirror CRF-R design. As would be expected, the CRF450X features a wide-ratio five-speed gearbox that's tougher than ever for added durability, plus lower final-drive gearing than the motocross version of the 450. To give the 450X a more tractable power delivery, Honda's engineers also added more mass to the AC generator and flywheel for improved low-speed power. In addition, there's a new exhaust system tuned specifically for off-road use via a longer head pipe, and it's capped off by a USDA-qualified muffler/spark arrestor.

Built to take on the world

To better equip the 450X to fulfill its varied off-road missions, fuel tank capacity now stretches to 2.27 gallons, enough for a 50-mile loop and then some. Compared to the R model, the seat is wider and sports rounder edges, and it's built with a different foam density designed for long-range comfort. Even the aluminum Renthal handlebar contributes to rider comfort by passing less vibration on to the rider. Another nice touch for off-road applications is the addition of an engine guard to provide more protection for the engine cases. A powerful 35-watt halogen headlight pumps out plenty of illumination after dark, and a trick but eminently practical LED taillight has been integrated into the rear fender. As would be expected, an easy-to-read, resettable three-digit competition-style odometer rounds out the package. Add it all up, and the sum of these parts leaves nothing to be desired, whether you're plonking down a trail for fun or flogging your way to the last checkpoint to take the overall win.

Riding enthusiasts who are serious about obtaining the ultimate off-road machine often put out the call for a motocrosser with lights. That's to be expected, since these high-flying MX machines normally represent the most advanced technology you can buy. However, Honda has taken the cutting-edge technology of its beloved 450R four-stroke motocrosser, and infused specific off-road technology through and through to create an all-new off-road machine with performance unmatched by anything in its class: the 2005 CRF450X.