Kawasaki recently unveiled its latest motocross bikes for the 2015 model year. Although they aren't significantly different from the 2014 bikes, Kawasaki says it learned a number of things from team rider Ryan Villopoto during the 2013 AMA Motocross and 2014 AMA Supercross title-winning Monster Energy seasons on the KX450F factory bike as well as the KX250F’s of the factory-backed Pro Circuit Kawasaki team. Kawasaki put its engineers to work to update the new KX250F and KX450F to enhance the power and increase durability of the four-stroke engines. They also worked to upgrade the Showa suspension, make the chassis lighter and slimmer on both models, as well as improve the braking components. Sounds like a recipe for success to us.

2015 Kawasaki KX450F
It’s not like the KX450F’s 449cc, fuel-injected, DOHC, single-cylinder four-stroke engine needs more power to be a serious contender in the class, but that doesn’t mean they didn’t make a few updates to the power, as well as focusing on upgrading the chassis, suspension and brakes.

Although the 2015 KX450F keeps the same 96.0×62.1mm bore and stroke as the 2014 model, it gets a revised version of the F1 auto-style “bridged box” piston first found in the previous model. The new piston is designed to be a duplicate of the one found in Villopoto’s factory bike, featuring short skirts with reinforced external ribs on the underside to improve its rigidity. The new piston provides a slightly higher compression ratio of 12.8:1 versus the 12.5:1 in 2014. The piston also contributes to giving the 450F motor a little more growl and an improved mid-range hit and a more robust top-end compared to the 2014 model.

Fine tuning of the engine can be made thanks to Kawasaki’s revolutionary DFI couplers, which allow the rider to change the fuel-injection mapping from the Standard map to Hard or Soft maps to adjust the KX-F to changing track conditions. The DFI coupler cap is easily accessible, so changing settings only takes a few seconds.

Kawasaki also added a revised ECU on the 2015 KX450F, which is designed to aid in traction by quickly retarding the ignition when rear-wheel speed increases too quickly. Kawasaki reminds us that the ECU is still fully re-programmable, and custom maps can be created with Kawsaki’s optional Kawasaki Racing Software Kit, which is the same tool used by Kawasaki factory and privateer race teams.

Kawasaki will again offer its Launch Control system to the motocross world, which is something other manufacturers have started to emulate. Kawasaki’s groundbreaking version functions by retarding the ignition in first and second gears to increase rear tire grip in low-traction situations. By simply pressing a button the system is activated, and it functions in neutral, first or second gear. Once out of the hole, the system deactivates and returns ignition timing to the stock setting when third gear is reached.

The 2015 KX450F’s also featured front and rear suspension components by incorporating Showa’s latest Separate Function Fork (SFF) with a Triple Air Chamber (TAC). The SFF-Air TAC separates the damping forces into the left fork tube, while a pneumatic spring is housed in the right tube. The design is intended to provide less friction and is lighter in weight than a conventional spring fork.

The Triple Air Chamber fork features three separate chambers with individual air volumes that allow more precise adjustability via individual tuning. An inner 145psi high-pressure pneumatic chamber works in harmony with a 7.25psi low-pressure outer chamber and a 130.5psi high-pressure lower chamber to replace the conventional steel coil spring. Kawasaki says that the air spring setup does reduce oil contamination simply because there is no metal-on-metal contact to initiate friction. To make the suspension action even slicker, the SFF-Air TAC also uses a titanium coating on the inner side of the tube.

Suspension tuning with the Showa SFF-Air TAC is easily accomplished via a Kawasaki Genuine Accessories 0-300psi Digital Air Pump that is included with every KX450F. That, in and of itself, speaks volumes about Kawasaki’s effort to bring high value to its customers. Some other manufacturers with air fork-equipped models don’t even include a pump with their bikes! The pump’s digital display offers the rider a way to precisely tune the air pressures, and as an added feature, the casing handily stores the DFI Couplers for the fuel injection system. That’s not a bad feature, as we have lost a few modules and even unwittingly taken modules meant for another brand to the track.

In the rear, the 2015 KX450F’s Uni-Trak linkage rear suspension gets revised valving in the Showa piggyback reservoir shock for improved damping in high-speed conditions. To reduce friction, a slick Kashima coating inside the shock body is used for smoother suspension action.

Kawasaki tweaked the KX450F’s handling and chassis feedback on the 2015 model by making adjustments to the aluminium perimeter frame, or more specifically, its rear subrame. A lighter subframe has been incorporated to improve mass centralization for quicker handling and a more nimble feel in the saddle.

Kawasaki engineers have also fitted a new, 270mm oversized, petal-shaped front brake rotor designed in conjunction with world-renowned supplier Braking. The 20mm larger front rotor is paired with a 240mm Braking rear rotor, and both are petal-shaped to shed mud in sloppy riding conditions and maintain more consistent braking performance. The KX450F’s axles are also new for 2015, lightened by 31 grams up front and 32 grams out back.

For added comfort, Kawasaki offers a four-position upper triple clamp that features two sets of handlebar mount slots to allow the rider a choice of four handlebar positions—25mm forward, 15mm forward, standard or 10mm rearward. The footpeg brackets allow the rider to leave the footpegs in the standard position or lower them by 5mm. Other comfort details include careful flush-fitting of the seams between the radiator shrouds, seat and side covers to help avoid riding gear snags for freer movement on the bike when transitioning from standing to seated, such as when cornering. The KX450F’s compact fuel tank is also designed to form a smooth straight line with the seat, allowing easy rider movement.

The KX450F also gets a new graphic design for 2015 with a Lime Green finish and factory-style decals. Green-anodized engine plugs, oil cap and generator cover plugs, as well as green alumite suspension adjusters and black alumite wheels give the big KX an aggressive, factory fresh look that is expected to last, as the coated components are corrosion and scratch-resistant.

2015 Kawasaki KX250F
Kawasaki’s 2015 KX250F four-stroke motocross model has a impressive winning pedigree. Kawasaki stepped into the new year by adding several key improvements to an already strong engine package in 2014, including the KX450F-derived Launch Control mode to adjust the bike’s power characteristics to improve traction off the line, as well as plug-n-play DFI couplers that allow the rider to alter the fuel-injection mapping and tailor the engine’s power to track conditions and rider preference. The quick and easy DFI coupler swap allows the rider to select between smoother, standard or harder-hitting power. For 2015, the KX250F receives even more engine updates to improve durability under stress of competition.

The KX250F’s liquid-cooled, DOHC, 249cc engine has the same bore and stroke as before, at 77.0×53.6mm, but it has a new reinforced “bridged box” piston like the KX450F. The new 250 piston is slightly heavier than the old one, and Kawasaki says the weight penalty was mitigated by a new piston pin that is lighter than last year’s pin without sacrificing durability.

The KX250F also receives a slightly heavier ignition rotor, weighing 9.5kg-cm compared to the 2014’s 9kg-cm unit, to smooth out the power and improve traction when driving out of corners.

Kawasaki was the first manufacturer to use a dual-injector fuel injection system on a production 250cc four-stroke motocross bike. Its Keihin Digital Fuel Injection (DFI) system uses a 43mm throttle body with a second injector that delivers an extra squirt of fuel (above) under acceleration to maximize power, particularly at higher rpm. The second injector is located higher up in the air duct, which is claimed to create a wider and more potent powerband. Kawasaki has made a slight revision to the system in 2015 by reducing the downstream injector droplet size to 75 microns; the upstream injector still sprays particles with a droplet size of 120 microns. The finer size and wider spray pattern of the downstream injector is intended to fortify the KX250F’s low- to mid-range power and improve throttle response. Revised ECU settings match the injector and magneto rotor changes.

The KX250F’s suspension settings, chassis and brakes all got updated this year. In the front, the KX250F keeps the 48mm Showa Separate Function Fork (SFF) that it introduced to the class in 2011 rather than getting the new SFF-TAC air fork. The SFF fork’s fork leg houses steel coil spring and incorporates a preload adjuster that simplifies preload and ride height adjustment with the simple turn of a wrench rather than requiring fork disassembly to accomplish the task. The left tube, which houses the damping system that controls ride quality. The SFF fork features 30mm main- and 35mm sub-pistons that move more oil volume at a lower internal pressure to keep the fork action smooth. Other friction-reducing efforts include a super-hard titanium coating on the inner fork tubes to prevent stiction and improve overall fork action.

In the rear of the 250 is a fully adjustable Showa piggyback reservoir, but it has been revised with firmer damping specs to match the fork. The state-of-the-art shock features high- and low-speed compression damping adjustability, and Kawasaki engineers added self-lubricating alumite coating on the inner surface of the shock cylinder wall to reduce friction. These features are designed to help increase rear-wheel traction and power transfer to the ground.

The KX250F’s chassis now carries a slimmer subframe much like the KX450F to improve mass centralization and allow easier rider movement in the cockpit. It also gets the four-position upper triple clamp that features two sets of handlebar mount slots to allow the rider a choice of four handlebar positions—25mm forward, 15mm forward, standard or 10mm rearward, and the two-position footpeg brackets.

The KX450F and KX250F receive a new 270mm front brake rotor designed in conjunction with aftermarket brake manufacturer Braking. The new wave-style rotor is 20mm larger in diameter than the old rotor. A Nissin two-piston front caliper supplies the clamping force.

The KX450F and KX250F receive a new 270mm front brake rotor designed in conjunction with aftermarket brake manufacturer Braking. The new wave-style rotor is 20mm larger in diameter than the old rotor. A Nissin two-piston front caliper supplies the clamping force.

To improve braking power and feel, the 2015 KX250F is fitted with the same 270mm oversized Braking-brand front rotor found on the KX450F—it’s 20mm larger than the 2014 rotor. The rear rotor still measures 240mm, but both have a factory-style petal design that is intended to shed mud more easily and look more stylish. The KX250F’s axles have also seen a slight weight reduction of 31 grams up front and 32 grams out back.

Completing the KX250F package are new-for-2015 styling cues that include green-anodized suspension adjusters, engine oil cap and generator cover plugs, and black alumite-coated wheels. Kawasaki’s embossed design on the clutch cover also features a nifty trick—the logo gradually reveals itself as contact from the rider’s boots wears away the painted surface.

Price and availability for the 2015 Kawasaki KX450F and KX250F are yet to be announced. For more information, contact your local Kawasaki dealer or visit www.kawasaki.com.