2005 Honda CRF250R Technical Changes
9/24/2004 3:22:00 PM
When Honda unveiled the innovative four-stroke CRF250R motocrosser in 2004, this lightweight quarter-liter revver immediately captured the hearts and minds-and stopwatches-of the racing public and magazine editors alike. Universally praised for its nimble feel, responsive handling and impressive power with a stratospheric 13,000-rpm ceiling, the new CRF quickly became a class-leading favorite.
But that was just for starters. Essentially, the development of this amazing new machine never even paused. With the 2004 racing season underway, the Honda Red Riders proceeded to push the CRF250R harder than any other racers on the planet-the ultimate test of a machine. Technical insights gleaned from the crucible of top-level racing have yielded improvements directly incorporated into the 2005 machine. As a result, the 2005 CRF250R boasts significant changes in both the engine department and rolling chassis-advancements that will continue to keep the CRF out front and pulling away from all challengers.
The 2005 CRF250R boasts a revised engine that sacrifices nothing in terms of top-end power while gaining a healthy boost in midrange grunt. Such a claim may sound like hype, but in truth, it's just plain sound engineering backed up by endless hours of work. When comparing the 2005 CRF250R to the 2004 model, dyno charts reveal just a pinch more peak horsepower for the new machine at the same 11,000-rpm engine speed, but this 2005 engine churns out a distinct advantage from 6000 rpm all the way up to the power peak. The meatiest portion of this jump in power takes place from 6000 rpm to 9000 rpm-just the ticket for blasting out of corners or sparking the perfect launch over a double- or triple-jump.
To create such an impressive increase in midrange power, Honda engineers developed a new camshaft and altered the intake port shape. The new port shape is an oval configuration designed to boost intake charge speed for even greater throttle response. Revised ignition mapping and a new exhaust system work in concert with these changes to further enhance these improved power characteristics.
A host of other changes to the engine refine the CRF's performance and further reduce weight. A new-style spark plug incorporates a side electrode for quicker spark production and improved flame propagation within the combustion chamber. An aluminum spark plug tube yields a small weight savings, and a new exhaust headpipe and a new muffler design shave 9.8 ounces from the complete exhaust system compared to the 2004 design. A new right-side engine cover also yields a weight savings while redirecting oil travel for improved lubrication of the clutch and gearbox. New clutch springs beef up clutch action and durability, and new shift forks, shift drum and shift shafts yield slicker and more precise shifting action
Significant changes to the suspension system make the CRF250R an even more stellar performer for 2005. Much attention focused on the swingarm, which features a redesigned swingarm shape with taper down the top of the swingarm as well as along the bottom. These alterations netted a substantial savings, 6.3 ounces of unsprung weight. Remarkably enough, even with this weight-loss regimen, the swingarm's excellent flex characteristics remain essentially unchanged.
These changes to the swingarm required relocation of the shock mounting point, and as a result the new shock is marginally longer (488.5mm to 499mm, eye-to-eye distance), while offering the same amount of shock stroke (133mm) as in 2004. The 2005 CRF250R also incorporates a new, lighter rear wheel hub, a change netting a further 4.2-ounce reduction in unsprung weight.
Up front, the front axle offset has also been tucked in 2mm (35mm to 33mm) to improve fork action by reducing fork-leg binding resulting from flex. This incremental change also places more weight on the front end for improved steering characteristics.
With its increased mid-range punch, a sharper-turning chassis, plusher suspension and a focus on reducing unsprung weight, the 2005 CRF250R has evolved from a great bike into a race machine that is truly awesome.