At the freezing Barber circuit, Duke Danger spins some laps on what might be the best-handling Ninja ever, the 2007 Kawasaki ZX-6R.
Pity the poor engineers of supersport bikes, forced to juggle seemingly contradictory design directives. It’s got to look bitchin’ but it can’t cost too much, and don’t forget to make it go around a racetrack quicker than any of its rabid competitors.
Reflect back just 10 years and you’ll see the middleweight class composed of bikes that could easily be used for regular commuting or some light touring, with handlebars mounted above the triple-clamps, accommodating footpeg placement and some storage under the seat. Those days, like the hotel TV set of a petulant rock star, are gone out the window. Now a sporting middleweight needs to be the sharpest tool, as a rider shouldn’t be forced to ride anything but the pinnacle of sportbike technology – the most capable scalpel extant.
“This is a full-blown race bike,” said Kawasaki’s Karl Edmondson during the bike’s press introduction at Barber Motorsports Park in Alabama.
And on the hugely fun and wildly undulating 2.3-mile Barber circuit, the new ZX feels kind of like a race bike. It doesn’t take many laps to gain a sense of trust, and it responds unequivocally to a rider’s inputs. It feels taut and confident, perhaps more so than any previous Kawasaki.
So how’d they do it – make a better bike than the excellent one that came before it – this time?
A cheater no more. For 2007 Kawasaki reduced the displacement on its ZX-6R down from 636cc to the same 599cc as its Supersport rivals.
It all started where they all do: the engine. In this case it’s new from the cases up, the first total redesign for Kawi’s middleweight in 10 years. For starters, it was left in the dryer a really long time, shrinking 40mm in both length and width; that’s getting on close to 2 inches for those not good with the metric system. Its narrowness was made possible by snuggling its four cylinders closer together, while it was shortened by placing its crankshaft, primary drive and countershaft gears in a tight triangular arrangement like its classmates.
Inside this new architecture reside some reminders of last year’s ZX-6RR motor, the 599cc one built for racing. They share the same bore and stroke (67.0mm x 42.5mm), as do the rest of the class challengers. There will be no more cries of “cheater bike!” because Kawasaki will no longer build the 636cc version it’s had in the lineup since 2003.
Like before, a set of oval 38mm throttle bodies mix air and fuel, but they are now 8mm shorter which might offer a high-rpm benefit. Like the 6RR, the intake ports are polished for cleaner, faster flow to the 1.5mm larger intake valves (26.5mm) operated by new cam profiles. The forged, short-skirt pistons are lighter, and even the piston pins weigh less, as do the forged- and sintered-aluminum valve spring retainers that reduce weight by half compared to steel pieces. The intake mixture is squeezed at a lofty 13.3:1 compression ratio, which seemed high until I noticed the 13.9:1 ratio of the old 6RR. Exhaust is routed though header pipes that curve sexily before routed into the under-engine pre-muffler/catalyzer; this allows the undertail muffler to be smaller for a tidier tailsection.
So, smaller engine, smaller bike, right? Er, no actually. It’s taller and wider, though just fractionally, and it’s longer by 1.6 inch. And the new bike must’ve been born shortly after Thanksgiving, as the specs say it weighs 6 lbs more than last year. If true, it would put the ZX’s weight at about 402 lbs with its tank empty. That’s still lighter than Suzuki’s Gixxer 600, but it might be as much as 19 lbs more than the radically slimmed down ’07 Honda CBR600RR.
The ZX-6R’s new, smaller engine gets air through polished intake ports and 1.5mm larger intake valves. The emissions get channeled through a pre-muffler/catalyzer located under the engine, which allows for a smaller undertail muffler.
You’d never guess any of this when you sit on the ZX, as it’s slimmer though the middle and a rider sits closer to the front wheel, giving the bike a more compact feel. Bars are closer to the rider and lower. It’s a racier place to do business, with footpegs that are placed closer together thanks to that narrower motor.
So let’s fire it up, then. Hopefully your first experience on the Zixxer isn’t in the 23-degree weather that greeted me for my debut session on a track I hadn’t seen before. Nevertheless, I had a job to do. Thankfully our bikes had tire warmers (“Uh, could I stick one of those in my pants.?”), and the Bridgestone BT002 Pros proved to have surprisingly good grip even in these cold conditions. The “Pro” version of the 002s debuted earlier this year, and the medium-compounds we rode on at 28 psi received rosy comments from the assembled scribblers.
Kawasaki’s PR literature claims the new 6R “churns out way more midrange torque than its predecessors,” but whoever wrote that must not have ridden the burly ZX-636. Perhaps they were referring to the old 6RR that was quite wimpy at lower revs. Still, this new bike doesn’t feel especially grunty halfway around the tachometer. It sings up top, though, pulling strongly from 10,000 rpm to its 12,500-rpm peak but with room to spare to its 16,500 redline, again same as the old 6RR.
A glance at the spec charts offers what might be seen as a worrying sign to number crunchers. This ’07 ZX is rated at 116.4 hp. Not only is that down from the 124-pony claim of the 636cc 6R, it’s also virtually identical to last year’s 599cc ZX-6RR.
(As with the previous gen ZX-6R, ECU tuning on U.S. and Canadian models has strangled the top-end power by closing the exhaust powervalve at high revs to meet noise regulations. The European model makes a claimed 123.3 ponies, a healthy boost of almost 7, plus it allows the engine to pull stronger up top, making its peak power 1500 rpm higher. This might be sad, but only if we didn’t know how to trick the ECU to default to the Euro spec settings with a free 5-minute mod you can read about here.)
The 23-degree temps at the Barber ZX-6R intro may have been chilly, but at least Duke was able to find one with a warm color scheme, one of four colors available.
Is this progress? Yes, according to the ZX’s engine designer, Takahiro Ono. He notes that getting around a racetrack quickly isn’t just a matter of how much power you have, but how early you can dial it on and how well you can put it to the pavement. As an example, he related to me of how the new 800cc MotoGP bikes have been breaking lap records in pre-season testing despite having 24% less displacement than their 990cc forbears. Closer to home, Kawi’s engineers claim the ’07 bike can lap Kawi’s Autopolis racetrack a good 2 seconds quicker than the old RR and at least 3 seconds quicker than the ZX-636.
Whether that’s true or not is difficult to say from my seat, but I can attest to a highly cooperative machine, and it’s hard to imagine a better mount for learning, then strafing, the hills of the technical BMP. Throttle response is super smooth, with none of the on/off throttle abruptness we despise. Kawi says the ZX’s “modified flywheel mass contributes to increased traction,” which we’ll take to mean that it has more of it, and the theory seems to work.
Also aiding the rider is the ZX’s clutch and transmission. First off, kudos must go to the excellent slipper clutch – it’s as good as any OEM unit I’ve tried. Bang a quick and sloppy downshift into Turn 1 without caring about details like rpm, and the back-torque-limiting clutch simply allows revs to match wheel speed. In addition, its amount of slip can be fine-tuned by Kawi’s optional race kit pieces. Also available are two optional gear sets for the cassette-style transmission that enables trackside internal gearing changes, the only middleweight with this racer-desirable component. Shift action is light on the ZX, though it can get hung up if you’re not careful to let the lever drop all the way after an upshift. Gear ratios are closely spaced, which worked well at the racetrack, though it may not be as optimal for the street.
But where the new 6R really shines is in the corners. Kawasaki pumps up the fact that the bike’s chief development rider, Tomomi Manako, is a former 125cc GP rider, and this has supposedly resulted in a bike that boasts higher corner-entrance and mid-corner speeds. The chassis geometry points to nothing unusual, using the same 25.0-degree rake as last year’s 6R and a scant 4mm increase in trail. Its wheelbase is up 0.6 inch over the old 636 and nearly identical to the Double-R version at 55.3 inches.
The new 6R doesn’t have the grunt we loved about its larger-displacement ’06 forbear, but a quick tuning trick to get the ECU onto European specs will help add some juice.
In the morning I was enjoying the assuring stability of the bike, glad that a steering damper was on board to quell any headshake. It was a short while later in the pits when I confirmed that there is no such component on the 6R, a real testament to the core quality of the chassis. Still, fighting with the bars over one of Barber’s many rises can induce a minor bar wag, and Kawi offers a ZX-10R-style Ohlins steering damper through its race kit catalog for those who want the insurance it offers.
Some manufacturers like to flaunt percentage changes in torsional or lateral rigidity of their frames, but Kawi is more demure by coyly saying, “The frame’s rigidity balance was completely revised to enable the chassis to easily handle mid-corner surface imperfections without upsetting the bike.” Reading between the lines, they’ve probably reduced the lateral rigidity.
The front end provides the kind of direct response that entices a rider to turn it in a little quicker and lean it in a little further. This new ZX provides communication in bigger doses than any other Kawasaki. From a strictly handling perspective, this thing is going to run at or near the sharp end of the supersport field. It takes a fair bit of prodding before pegs are dragged, and ground clearance is certainly not an issue for any street riding.
A critical role in the handling equation is the suspension. The ZX still uses a 41mm inverted fork up front, but its spring is now located at its bottom, fully ensconced by oil to reduce oil cavitation. At the rear, the shock’s linkage now uses what Team Green call “pillow balls” where standard bushings are usually found (Insert lewd and juvenile joke here). Both ends are adjustable for preload and compression and rebound damping, and the shock gets the bonus of having its compression adjustments separated into high-speed and low-speed.
In addition to two mechanics in the pits, we had former World Superbike pilot Akira Yanagawa blazing around Barber and scrubbing in tires!
It seems like pillow balls are a good thing to have, as feedback from the rear end is generous. The front end is just as good. The braking bumps entering Barber’s Turn 5 were sucked up so nicely that I had to be told about the ripples before I noticed them.
Let’s also give praise to the Ninja’s brakes. These are the same 4-piston, 4-pad radial-mount calipers actuated by a radial-pump master cylinder we’ve enjoyed for the past two years of ZX-6s, but its 300mm rotors are now 6mm (from 5.5) thick to better shed heat without going to a larger-diameter disc. Ample power, no fade, and best of all, plenty of feedback. Zero complaints here.
And we can’t complain about the ZX’s hard-to-read tach any longer, as it’s now a simple white-faced analog rev counter with red numbers that take just a moment to assimilate. An unmistakable yellow shift light in the upper-left quadrant can be programmed to illuminate at whatever rpm you choose. I was happy to hear the ZX had a gear-position indicator, as it’s been our experience that they’re handy for riders of all talent levels, but Kawi just couldn’t give us a perfect set of gauges. I couldn’t believe my eyes when I saw the 6R’s indicator, as it’s so small that it’s useless. Well, it may be readable on an open highway in Nebraska, but certainly not when you’re screaming in to Barber’s Turn 1 at a-buck-thirty.
Other than that minor faux pas, our only reservation with the ’07 ZX-6R is with what seems to be a top-heavy powerband. Kawi talks about “a mile-wide” spread of power, but that might be a bit optimistic. It felt to me as if it might fall between the reasonable GSX-R and the Yamaha R6 screamer. From what Kenny tells me, new CBR600RR is in contention for the most desirable powerband of the 600s.
With its $8999 MSRP, the ZX is $300-$400 cheaper than the R6 and $500 less than the CBR (the GSX-R is just $8899). It was only a few years ago that middleweights crossed the $8000 threshold, and now they’re approaching $10K!
As for which bike is going to be the best overall supersport contender, it’s too early to tell. In the Kawi’s favor is its stellar handling and reasonable price tag.
The new ZX-6R should be hitting dealers early in the New Year in your choice of four colors.
Let us know what you think about this bike test in the MCUSA Forum.