2012 Kawasaki KX450F and KX250F Preview

Smoother, slimmer, faster and stronger

story by Dan Paris, Photograph by Kawasaki, Created May. 17, 2011
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Kawasaki has updated its KX450F and KX250F motocross bikes for 2012. Dan Paris gives us the details on Team Green's latest MX machines.

Everyone knows the KX450F rips. Rips tracks to shreds, rips your arms off … In a horsepower race, team Green sits on top.

For 2012, Kawasaki has taken steps to civilize the monster for 2012, starting with a two-mode ignition dubbed ‘Launch Control, which is tuned to improve off-the-line traction without sacrificing mid range or top end power. The push-button system is activated by a switch on the left handlebar that alters ignition timing in first and second gear. When the rider shifts into third gear, the EFI returns to the standard ignition map. Sounds like exactly what we’ve been begging for!

The big Kawasaki has also taken flak for being, well, big. A new frame and slimmer rider compartment, with a width reduction of 4mm across the main frame spars, give the 2012 KX450F its most slender mid-section ever. Chassis rigidity has been refined by altering the shape of the ribbing inside the new frame, creating more flex in the upper portion and stiffening the lower sections around the swingarm pivot. The seams between the radiator shrouds, seat and side covers are very flush fitting to help prevent snags.

2012 Kawasaki KX450F
2012 Kawasaki KX450F

The KX450F now comes with four different handlebar positions and two footpeg positions to better-fit different sized riders. Mass centralization and a lowered center of gravity were Kawasaki’s goals for 2012, so a new fuel tank, upgraded bodywork and a shorter muffler were designed to shuffle weight toward the center of the motorcycle. The new fuel tank also has a shorter overall height and a narrower top section, with a smoother tank to seat transition to improve rider freedom of movement. The tie rod arm of the Uni-Trak® rear suspension linkage is now slightly less rigid to improve rear-wheel traction. Kawasaki also offers an optional shorter rear suspension tie rod to reduce seat height.

The DFI system comes with three pre-programmed ignition maps that are changed without the use of a laptop computer. Maps can easily be changed to suit standard, hard terrain or soft terrain by swapping the DFI wire coupler cap clipped to the side of the steering head. The ECU is also programmable by using the accessory KX FI Calibration Kit that works with any computer running Windows 7.

The 2012 KX450F has improved mid- to high-end power and a wider powerband, thanks to a new bridge-box bottom piston that has been revised to enhance mid to high-rpm power. A thinner top piston ring with an upgraded surface treatment is used to reduce friction and improve throttle response. A new intake cam boosts power as well. The new header pipe is shorter and features a tapered mid-section. It bolts to a new silencer that is 60mm shorter than last year but has the same overall volume and meets 94 dbA noise regulations.

2012 Kawasaki KX450F

The five-speed manual transmission has an extra dog on the gears and a shorter shift fork to improve shift feel. First gear is thicker to improve durability. A new shift lever moves the pedal 3mm farther from the footpeg, and heavier clutch springs keep clutch slippage in check.

2012 Kawasaki KX450F

The Kayaba shock receives the Kashima Coat surface treatment to its internals. Kayaba’s Air-Oil-Separate (AOS) fork keeps oil and air in separate chambers for stable damping performance, and 2012 Kawasaki KX450Fit’s mated to a revised lower triple clamp. The super-hard Diamond-Like Carbon (DLC) coating on the outer surface of the inner fork tubes and high-tech Kashima Coat treatment on the inner surface of the outer fork tubes help deliver supple action.

A blue alumite finish on the oil cap and generator cover caps highlight the upgraded appearance of the KX450F motor and match the blue finish on the suspension adjusters and new graphics. The embossed logo on the clutch cover features a raised Kawasaki insignia that is revealed as the black paint is worn away by the rider’s boot.

The changes announced for the 2012 KX450F address our few concerns about the 2011 model, and we can’t wait to ride it at the famous Red Bud AMA Motocross track next month. The 450F will be available in Kawasaki Lime Green, with black alumite-coated rims, blue anodized highlights and aggressive graphics at a price yet to be shared.

2012 Kawasaki KX450F

Next Page ... 2012 Kawasaki KX250F

2012 Kawasaki KX250F

Not only is the KX250F the winningest bike in AMA Supercross, it’s one of the best performing bikes no matter where you race it. We loved it when we tested it in 2010, then loved it even more with fuel injection and the Single Function Fork in 2011. We’re stoked to hear that Kawasaki has made changes to improve power, increase durability and tighten up handling for 2012!

For 2012 the KX250F gets even more top-end power thanks to a dual-fuel injector system, which has a second fuel injector located in the airbox to help build a wider spread of power as revs climb. Think of it as an EFI version of the power-jet, delivering an extra dose of fuel when accelerating to increase top-end power and overrev. An updated ECU has increased power to run the digital fuel-injection system, and can be calibrated with improved software and any laptop computer that runs Windows 7.

2012 Kawasaki KX250F

The crankshaft has been upgraded to improve reliability and balance, and the bridged-box bottom piston and cylinder walls feature a new surface treatment to improve long-term durability. The connecting rod has a thicker stem to improve strength. The transmission has a shorter stoke of the shift fork and solid shift rods to give the rider a more positive gear selection feel.

2012 Kawasaki KX250F

2012 Kawasaki KX250FThe stainless steel and aluminum exhaust system has a high volume and is designed to meet 94 dbA noise requirements.

The Separate Function Fork (SFF) gets a stiffer spring rate this year, a longer rebound spring and altered valving to improve initial feel. The external preload adjuster and slippery titanium fork tube and Kashima inner treatment remain for 2012.

The Showa shock also gets a stiffer spring and a re-valve to refine damping. Monkey motion is supplied by a new suspension linkage with a thinner, less rigid tie-rod to improve traction.

New bodywork includes a one-piece shroud and number-plate design, as well as a new seat that is more resistant to wear. The KX250F is still full of quality components, such as a Renthal bars and black alumite-coated rims. A rib-less rear hub and butted spokes further reduce unsprung weight. New graphics and anodized bits make the 2012 KX250F look trick.

To keep the KX250F’s reputation as a versatile race bike, it has optional goodies like a fuel-injection calibration kit, different weight magneto rotors, oversized handlebar adaptors, aluminum or steel rear sprockets, solid brake rotors and different rate springs.

2012 Kawasaki KX250F
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