Kawasaki hopes to stimulate the sportbike world with the return of a cult classic: the 636-powered 2013 Kawasaki Ninja ZX-6R ($11,699). Team Green’s latest creation overlooks antiquated engine capacity limitations by incorporating a stroked 600cc-based engine to boost acceleration right where you need it whether your ride on the street or track.
The basic architecture of the Ninja’s liquid-cooled Inline-Four engine, including its case and 67mm bore dimension, is the same. Piston stroke however has been increased 2.6mm to 45.1mm. This nets a 37cc increase in engine displacement (636cc). Other key updates include the fitment of pistons with an updated crown design to accommodate the revised high lift valve timing specification. New shorter connecting rods and a new crankshaft were also installed while the engine’s compression ratio was reduced slightly by 0.4 to 12.9:1 due to the bump in engine capacity.
(Top) Increased piston stroke boosts the engine’s capacity to 636cc. (Center) The extra mid-range power allows the rider to carry a higher gear through many corners. (Bottom) Both the European and U.S. spec ZX-6Rs are in the same state of engine tune for 2013.
Many of the intake and exhaust components were also modified for improved efficiency. The fuel-injection system now employs only four injectors instead of the previous dual-stage eight injector set-up. The new injectors are capable of delivering a higher, more finely dispersed volume of fuel. The shape of the engine’s intake and exhaust ports were also altered to compensate for the added flow. Since the upper fuel-injectors have been removed, the volume of the airbox could be increased. Lastly, the velocity stacks atop the throttle body were also lengthened for greater engine performance at low rpm.
The exhaust was overhauled and the stainless-steel headers now employ cross-over tubes linking all four cylinders thereby enhancing the engine’s torque output at low-to-medium engine speeds. The muffler has a sleeker and more triangulated shape and both the U.S. and European ZX-6Rs now feature identical states of engine tune and power.
You wouldn’t think a 6% increase in engine capacity would make such a difference on the road—but it does. Bottom-end power is snappier, but it’s the mid-range where the engine’s added ‘oomph’ is most noticeable. At northern California’s Thunderhill Raceway Park, site of this year’s Superbike Smackdown IX Track test, the Ninja drives off corners hard—especially when the tachometer needle is pegged around 8000 revs.
The added grunt allowed us to run the bike a gear high, much like you would a Ducati 848 or a Suzuki GSX-R750. Top-end power was good—on par with the old machine, however it flattened out near redline. Still the engine spools up quick and offers lots of over-rev. We also love how softly the rev limiter intrudes which makes the bike feel like it will never stop accelerating. Equally as pleasing is the roar of the engine. It begins as a racy induction howl and transforms into a maniacal high rpm shriek that will make your eyelids flutter with euphoria. The engine is pretty well balanced though it does transmit a small degree of vibration through the handlebars which was only noticeable during the street ride.
(From full stiff)
Ride Hight: 6mm (via shim)
The Ninja’s drivetrain also received some improvements in an effort to make it friendlier to ride on the highway. The big news is the fitment of a clutch sourced from Japanese company Fuji Chemical Company. The wet-style clutch is similar to the Ninja 300‘s and features a more simple design allowing for fewer mechanical parts and less weight (over 1.5 pounds lighter than the old unit). A cam system pushes the clutch plates together when the engine is loaded (acceleration) and apart during deceleration. This allows for fewer clutch springs (from six to three) and wispy, one finger light lever pull. While this facilitates a degree of back-torque limitation (rear wheel chatter) conversely it can no longer be deemed a true tune-able ‘race-style’ slipper clutch.
(Top) A shorter first gear and new clutch design that offers reduced cable tension makes the Ninja a better street bike. (Center) Although it changes gears easily we wish it had the speed of an electronic quickshifter. (Bottom) The influence of Kawasaki’s aerospace group is obvious in the Ninja’s new styling.
We’ve never had an issue with the level of cable tension required to depress the ZX-6R’s clutch lever, but the updated design proves to significantly reduce lever pull, requiring no more than one finger. It also offers a relatively wide range of engagement which makes it easy to get off and running. Out on track the clutch proved to work well under hard deceleration with it keeping the rear wheel inline with zero chatter. On the street we did notice that it didn’t offer as smooth actuation as the old unit under the most extreme conditions when you’re purposely sliding the back tire with the rear brake.
The ZX continues to employ the same stacked cassette-style six-speed transmission except the thickness of the gears has been increased to compensate for the added torque of the motor. First gear has a lower ratio which makes the bike easier to launch from a standstill as well as enhancing straight line acceleration. Lastly, a lighter O-ring drive chain was fitted. Final drive gearing remains unchanged at 16/43.
As we mentioned before, the engine’s broader powerband allowed us to actually carry a higher gear around many of the corners on track and complemented the bike’s final drive gearing well. Our only really complaint is the lack of an electronic quickshifter, especially since the hardware is becoming standard on other brand’s offerings.
Kawasaki’s involvement in the aerospace industry is obvious when you see the ‘13 bike’s lines. The air intake is larger and the forward fairing is positioned at a sharper angle for decreased drag and to better shield the rider’s extremities from wind. The headlamp beams, turn signals and LED taillight are also updated and said to offer greater brightness and visibility than before. We’ll have to take Kawasaki’s word for it as we didn’t have the opportunity to ride the bike after dark. Another nice touch is the pentagon-shaped mirrors which provide a wider view from behind.
(Top) The ZX-6R steers easier and is much more precise than ever before. (Center) The new BP-SFF Showa fork separates spring preload and damping adjustment between legs. (Bottom) The Ninja still handles great but it lost a small degree of feel and cornering prowess near maximum lean.
The primary components of the ZX-6R’s chassis, including the frame and swingarm, are untouched for ’13. What has changed however is the castor angle (from 24 to 23.5-degrees) in an effort to sharpen steering. Complementing the change is a new steering stem seal that is claimed to further reduce any binding.
Both front and rear suspension components are new and feature the latest technology from technical partner Showa. The fork now employs Big Piston Separate Fork Function (BP-SFF) design which makes use of a coil spring in each leg. Adjustment is split between legs with the left housing spring preload adjustment. The right leg offers compression and rebound damping tuning.
Adjustments are made atop each leg which makes dialing in the damping settings less of a chore. The set-up also uses fewer components thereby reducing weight, and of course cost. The gas-charged shock also received some attention and is now nearly one inch longer from eyelet to eyelet. The spring rate has also been reduced by 7.5% and it operates within a more progressive linkage. As before the shock offers spring preload, compression and rebound damping adjustment.
Predictable, rock solid handling has been a hallmark feature of Kawasaki’s middleweight since its last major overhaul (2009), and the new bike expounds on those characteristics by offering quicker steering than ever before. In fact it turns into corners so sharply, and with such little effort, it’ll take some time for your brain to adjust to its precision.
The damping settings controlled chassis pitch without flaw during all-out braking and acceleration but felt like it lost a degree of its hard core track ability at that nine-tenths level. But it’s a small compromise based on how well the bike’s suspension works on the street. Granted, the freshly paved rode we treaded on during the course of our 70-plus mile street ride was smooth but the Ninja’s suspension glided over the occasional bump while still serving up a sporty but not overly taut ride.
(Top) Chassis stability under braking is tremendous allowing the rider to run deep into corners. (Center) Nissin has developed an alternative to Brembo’s ultra-popular monobloc caliper. The Japanese version performed as advertised.
Last year’s Ninja was certainly not lacking in terms of stopping power. But the new model aims to evolve performance with the introduction of new-generation monobloc-style calipers manufactured by Nissin. The calipers employ 32mm pistons compared to the 30/32mm combination before. The design also allows each binder to be more rigid and lighter, too. The calipers clamp to larger diameter petal-style rotors (up 10mm to 310mm). In spite of the bigger size the weight of the discs is unchanged since the thickness has been reduced by 1mm to 5mm.
The 220mm rear disc brake is also new and borrowed from the Ninja ZX-10R. A new Bosch-sourced ABS system is now available for a $1000 upcharge. The package offers only one fixed mode and cannot be disabled. It also adds almost five pounds to the weight of the motorcycle. The machines we rode were not fitted with the ABS option so we’ll have to reserve comment for a later time.
On the track the Kawasaki’s brakes proved to be downright spectacular. We’ve spun a lot of laps at Thunderhill and we were amazed by how deep the Kawasaki would run into corners. A firm two finger pull on the front lever netted outrageous stopping power with a matching level of feel—and the best part is that the chassis stayed glued to the ground without excessive pitch (credit also goes to the new fork). The brakes do fade ever-so-slightly under prolonged heavy use which necessitated us adjusting out the position of the lever but given the six-levels of available adjustment it’s a moot point, unless you have crazy large hands and you constantly lean hard on the brake lever.
The Kawasaki continues to roll on black six-spoke cast aluminum wheels (the front hub has modified slightly to work with the updated braking set-up) shod with Bridgestone’s S20 high-performance road tire in sizes 120/70-17 front and 180/55-17 rear. We had limited time on these tires but they served up plenty of grip for medium-to-fast paced cornering maneuvers and warm-up time was quick, too.
Kawasaki trickles down its advanced electronics package as used on its other top shelf sportbikes. The ZX-6R rider can now choose from two separate engine power modes: Full and Low. As the name implies, Full power mode allows access to maximum engine performance, all the time, at any rpm. Low power also cranks out maximum engine torque at lower revs, however at a certain rpm
(Top) Kawasaki is the first Japanese brand to outfit its middleweight bike with traction control. It also comes with two engine power modes.(Bottom) Kawasaki’s traction control system continues to evolve positively. The latest system can make the bike friendlier to ride on the street and track.
threshold (approximately 8000 revs) it limits full power by 20% thru redline. Another benefit is the milder throttle response which helps make a novice rider more comfortable at the bike’s controls.
The ZX-6R’s traction control system is another first for the Japanese middleweight class. The set-up borrows technology from the Ninja ZX-14R including a pair of wheel speed sensors. The electronics monitor front and rear wheel speeds and compute data from the engine’s other sensors to calculate when wheel spin can potentially occur. For a more in-depth analysis of how the system works be sure to read the Kawasaki ZX-10R Traction Control Comparison.
Three-levels of adjustment (plus ‘off’) are offered. Level 1 is the least restrictive setting while Level 3 is the most. Additionally the electronics only modify the ignition curve in Levels 1 and 2. In Level 3 the computer can adjust ignition, fuel and the throttle bodies. This allows it to respond more effectively on slippery road surfaces. Each of the modes can be selected while riding however the throttle must be closed.
Due to their more mellow torque output it’s a fair assumption that most middleweight bikes don’t really need traction control. Still the functionality of the Kawi set-up surprised us. It was able to read the dynamic condition of the motorcycle even over hills and on high camber turns more accurately as compared to the ZX-10R. The electronics activated more smoothly which made it hard to even know if the system was online. This gave us confidence to lean on the electronics and ride it a bit harder than we would with it ‘off.’
Kudos to Kawasaki for stepping outside of conventional engine displacement category with the reintroduction of its 636.
Does the new 636-powered ZX-6R have what it takes to jumpstart the sportbike market? It could if you can overlook its $1400 price increase over last year’s bike. It blends some of the best features of the 600 class i.e. agility, low curb weight, rev-happy engine, with the extra mid-range snap of a big bike. Factor in the function of its traction control and separate engine power modes and it’s clear the green machine offers motorcyclists something more than what’s currently available in the middleweight class.