Rules are meant to be broken, bent or otherwise thrown out the window. If they weren’t, well, Kawasaki never got the memo. Case in point: Team Green’s 2013 ZX-6R, a bike that rips the middleweight-class convention to shreds by means of a 37cc displacement advantage. Anyone with a soft spot for Kawasaki’s middleweight platform and a decent memory will recognize the 636 moniker that goes along with the change; its (re)introduction comes just ten years after the launch of the original six-three-six. The ZX-6R’s design brief has been entirely rewritten for ’13 however, and two days spent riding the bike gave us a good indication of what that meant for the middleweight class: suffice it to say the other manufacturers are in for a rude awakening.
The biggest difference between the new ZX-6R and the no-longer-available, 599cc ’12 model is that its design brief puts greater emphasis on street performance and broad-based function. Kawasaki statistics support the change in pace, and suggest that 27 percent of sportbike owners have less than one year of riding experience. Surveys also confirmed that 82 percent of sportbike owners use their bike for commuting, while just 32 percent actually take their bike to the track.
Figures in mind, Kawi engineers went about upping displacement for better low-end and midrange power. The suspension, brakes and electronics received similar attention; changes include the addition of new Showa suspension, traction control, switchable power modes and an optional anti-lock brake system similar to what’s found on the Kawasaki ZX-10R ABS.
The list of modifications trickle off from there, which brings our attention back to the star of the show, the engine. Primary changes include a 2.6mm increase in stroke, which brings the measurement to 45.1mm and the total displacement of the ZX-6R to an even 636cc. Bore remains 67mm, but Team Green has widened the intake ports near the throttle bodies and stretched the exhaust ports near the valves to match the added displacement and improve power delivery. Hard parts are all-new, with revised cams providing increased intake duration as well as increased intake and exhaust lift. A reshaped piston crown is designed to work with the changes in valve lift, whereas 1.5mm-shorter connecting rods (with 2mm-wider stems) and straight piston pins add strength for better high-rpm durability. The compression ratio drops from 13.3:1 to 12.9:1 as a result of the internal changes.
The remainder of the ZX-6R’s improved engine performance comes in the form of a reworked air and fuel system. Changes on this front include a larger airbox that offers 12.5 percent more internal volume for greater peak power, longer intake funnels for low-end and midrange torque and injectors that deliver a sub-60 micron fuel droplet for improved combustion. Interestingly enough, Kawasaki engineers have increased fuel flow by upwards of 20 percent, which has also allowed them to use just a single injector per cylinder. New fuel injection settings counter whatever silkiness the ZX-6R lost in the departure of those second injectors, and also contribute to reduced emissions, claims Kawasaki.
Burnt gases are now expelled through a reworked exhaust that is both easier on the eyes and better in terms of performance. Biggest news is that all four header pipes are connected by crossover tubes, whereas in the past pipes one and two were connected separately from pipes three and four. Kawasaki claims the biggest benefit is, you guessed it, increased low-end and midrange torque. The new header pipe fits against a reshaped muffler that should appeal to riders without the budget for an aftermarket exhaust.
New cams provide increased...
New cams provide increased intake and exhaust lift, which necessitated new pistons with an altered crown shape. Compression ratio drops from 13.1:1 to 12.9:1.
Shock spring is 25mm longer...
Shock spring is 25mm longer for added rear ride height and 7.5 percent softer for more compliance over bumps. Link ratio is also more progressive.
An F.C.C. clutch uses two...
An F.C.C. clutch uses two types of cams to provide assist and slipper functions. Lighter and fewer springs (three versus six) provide a lighter pull at the lever, while the slipper feature provides stability under deceleration. We found it hard to fault either aspect on the track or street.
The exhaust is reworked from...
The exhaust is reworked from header to muffler. Biggest news is crossover tubes that now connect each of the four header pipes and a triangular muffler design that’s much easier on the eyes. A new heat shield has also been utilized.
310mm front brake discs are...
310mm front brake discs are 10mm larger than the rotors on the ’12 ZX-6R, but they’re also 1mm thinner and end up weighing the same. Nissin monobloc calipers are 90g lighter and provide superb power and feel without relatively any fade over the course of a 30-minute track session.
New KTRC and Power Mode switches...
New KTRC and Power Mode switches on the left clip-on allow you to set traction control settings between levels 1 and 3 (or off) and riding modes between Full and Low. Worth mentioning is that you can change TC settings while riding, although you have to come to a stop to turn the system off.
While Kawasaki has done its best to avoid discussing horsepower figures, the manufacturer did supply dyno charts in the ZX-6R press material which indicate a significant bump in torque and horsepower through the midrange. Kawasaki also suggests a .2 second advantage in the quarter mile, a quantitative number that provides at least a small glimpse of the new ZX-6R’s power advantage.
Additional changes to the engine’s architecture include a retooled transmission and new F.C.C clutch with assist and slipper functions. The clutch itself is similar to the unit found on the Ninja 300 we tested elsewhere in this issue and uses an assist cam and a slipper cam. The former helps push the plates together under acceleration and allows Kawi to use fewer and lighter springs (three versus six), which ultimately provides a softer feel at the clutch lever. The latter conversely reduces clamping force on the hub and operating plate under deceleration to promote some slip and prevent the rear wheel from skipping across the tarmac under extreme braking and downshifting situations. The transmission is updated by means of a shorter first gear and thicker cogs, which should increase user-friendliness from a dead stop and durability.
The ZX-6R’s Showa front fork is all-new and combines Separate Function Fork technology with a Big Piston Fork setup. Biggest difference is that preload adjustments are now made exclusively on the left fork cap (despite there being springs in both legs), whereas damping adjustments are made on the right cap. No word on spring rates for ’13, although Kawasaki admits to pulling the fork tubes through the triple clamp 2mm for better front-end weight bias. Resultant changes include a steeper, 23.5 degree rake measurement (versus 24.0 degrees on the ’12 model) and a slightly shorter trail. The rear shock has undergone like changes and runs a 25mm-longer spring for added rear ride height. Said spring is also 7.5 percent lighter for a plusher feel over bumps.
An SFF-BP fork means that...
An SFF-BP fork means that preload is adjusted exclusively on the left fork cap, whereas compression and rebound adjustments are made on the right cap. Mirrors are updated to provide a better view of what’s behind you, and the gauge cluster is designed to display each of the ZX-6R’s new electronic settings.
A set of Nissin monobloc calipers clamp down on a pair of front brake rotors that are 10mm larger in diameter but also 1mm thinner than the ’12 model’s discs. The clever design means the brakes are bigger for added performance but also identical in terms of weight when compared to previous brake setup. Out back, a ZX-10R-culled Nissin caliper works on a 220mm rotor.
A new electronics suite is the final piece to the ZX-6R puzzle, and is complete with everything from traction control to selectable ride modes. Full or Low engine modes can be selected via a switch on the left clip-on and provide varying levels of engine performance depending on road conditions. Full, for instance, grants access to every last bit of power, whereas Low offers a softer throttle response and limits power output through the midrange, ultimately offering you just 80 percent of the engine’s maximum power. The Kawasaki’s traction control system broadens the ZX-6R’s level of adjustment even further, and offers three levels of intervention plus off. Similar to the ZX-14R system, the S-KTRC on the new 636 controls the ignition in levels 1 and 2, but controls ignition, fuel and air supply in level 3.
The ZX-6R runs a larger ZX-10R-esque...
The ZX-6R runs a larger ZX-10R-esque intake duct and a larger airbox that features 12.5 percent more internal volume. The front cowl is reshaped to provide better airflow over the rider’s shoulders.
Hidden Agenda
The idea behind the new ZX-6R was to make the bike appeal to a broader range of riders (e.g. newer riders, street riders and the occasional track-day rider), but this bullet point is easy to dismiss once you throw a leg over the saddle. Ergonomics are identical to what they were a year ago, with the only difference being a minute change in feel thanks to new ride-height measurements. The design is just as aggressive as in years past due in part to a larger, ZX-10R-esque intake duct and sharpened cowls. Changes intended for the street, in fact, are limited to a new low-friction steering stem seal that lessens steering effort at slow speeds and a new mirror design that relocates the larger section of glass to an area that provides a better view of who’s in tow. Needless to say the bike feels just as aggressive as its track-bred predecessor from the helm.
Kawasaki won’t deny that the ZX-6R is in fact just as capable as the purebred ’12 model either, just that it’s more versatile. And to drive that point home, the manufacturer recently invited members of the press up to Northern California for a full day of track riding at the undulating Thunderhill Raceway in Willows, CA, and a separate day of street riding through Plumas National Forest. During the six-and-a-half hours of seat time that ensued, I could only come up with one conclusion: the 2013 ZX-6R is absolutely a better bike than its precursor.