Road Test

Kawasaki ZX-6R Review - 2/3

Kawasaki's ZX-6R has a reputation of being a serious track tool, wild to the point of instability. The 2007 model is both heavier and less powerful. Is this progress or a backward step for the 6R?

ENGINE

The 636 motor is stunning. Perhaps the capacity increase was expected (by you and me) to boost the mid-range. After all, anyone who's had a big-bore job on their motor will report they get a sizeable midrange boost as a result, but a lesser effect on top end. But the 636 wasn't a bored 600, it also had a longer stroke with no small amount of attention paid to the head and ports. The result wasn't an engine that leapt ahead out of the corners. Instead this was one that hung onto its power for longer. Post 12,000rpm when the regular 600s are fading the 636 is still storming on. Yeah, it's a revver. To ride a 636 fast you don't short shift and enjoy the midrange boost. No, you ring it as hard, if not harder, than any other 600. In return you get a few more mph on top and it charges through the standing quarter in just 11.1 seconds - just 0.2s off being a proper 1,000cc time.

So knowing that, it should be no surprise that the new super-revvy 600 motor feels almost identical to the old 636. To make it fly, you're seriously chasing that indicated 16,500rpm redline and as Kawasaki say, it's a stepless linear progression of power from beginning to end. What is a surprise is that it very nearly matches the 636 for both power and torque.

Kawasaki have gone to great lengths to achieve this. This is their first all-new 600 motor in 10 years, and it's been made more compact by 40mm both in length and width. There are new cam profiles, larger inlet valves, polished ports, a seriously high compression ratio and shorter throttle bodies. But perhaps it's because this is their first new motor for such a long time that the ZX-6R has gone from being the strongest engine in the class, to just about the weakest - although not by much. One year ago and the new engine would have been right in the game, but now it's second-rate. Maybe it's just down to who can deal with all the Euro3 bollocks the best.

However, both motors have to be given kudos for being great track motors. They hang on to their revs mid-corner and certainly don't do anything to upset what are both very balanced machines. One benefit they both offer the track rider is what is probably the best slipper clutch to be found on a standard machine.

For those unfamiliar with slipper clutches it really is a revelation the way you can simply belt into the tightest corner and slap down however many gears you choose and still find the whole plot stays in line - no lock-up, no distressed motor, nothing. More easily appreciated on the track than the road, but a useful little device nonetheless.

But the bottom line is that the new motor is 2.5bhp down and 8mph slower. Progress?

CHASSIS

We're not going to be able to criticise either bike here, they both handle so exquisitely well, but there does seem to be a quite stark difference that is much more pronounced than any difference in the motors.
The new ZX-6R design team apparently used the services of Akira Yanagawa as development rider. Much was made at the world launch of the team's intent to create enormous corner entry and mid-turn speeds.

Again we're talking all new chassis, new forks, shock etc. Not that the differences to the 636 chassis seem starkly different. The chassis is very similar to the older bike and the swingarm too, still featuring a gull-arm on the right side and a triangulated beam on the left. The exhaust still exits under the seat and when you sit on them, we're talking almost identical riding positions. Very similar seat heights, same low bars, impossibly low screen and highish pegs.

The difference comes in what can be best described as steering inertia. Tip the 636 into a bend and it's over. Quicker almost than you can respond, at least at first. Tip the '07 in and the progression is far more measured. There's a resistance such as you may feel when comparing feedback from a 180 to a 190-section rear tyre.

Trying to analyse the difference isn't easy. Wheelbases are only 10mm apart (the old bike is shorter) and the '07 has a steeper steering angle (24° as against 25°) and a 6mm higher seat. There's really not much in it, but the overall effect is pronounced. Tyres may have a significant effect then. The 636 came with Bridgestone BT-014s, the '07 with 015s (both OE fitments). At Brands Hatch the 14s took a full three laps to 'come in'. Those were a sketchy three or so laps, but after that the 14s had to be praised as a real scratcher's tyre.  You could really push on, the feeling being that the front was being pushed the hardest, but it never felt close to breaking away even when things started grounding out around Clearways.

Meanwhile, the 15s could be pushed after just the one lap of warm up. They offered comparable grip but felt just a bit more composed, the benefit of stiffer sidewalls.

Both had excellent brakes. There was never any question over the performance of the radial Tokicos on the 636. Perhaps the new Nissin radials had an advantage of being brand new (and four-pads-for-four-pistons in design), and they were certainly just that wee bit better in feel and strength.

Continue Splitting Heirs: 2005 v 2007 ZX-6R 3/3

WHAT WE SAID

2005 ZX636
"The ZX-6R is a track bike, no questions. The handling is brilliant, razor sharp and more precise than a German instruction manual. It attacks corners and leans forever and is just mental to ride." - Jon Urry

"(On the road) it's just so uncompromising. It has a habit of shaking its head, the riding position is too cramped and the engine screams. Everything that makes the Kawasaki great on the track makes it horrible on the road." - Niall Mackenzie

2007 ZX-6R
"The new motor is designed to be a perfect platform for racers to develop or track day nuts to thrash. Which is why the gearbox is fantastically slick, the slipper clutch excellent and it comes with a gear indicator and lap timer as standard. Rev the ZX-6R, treat the road like a track and it is stunning and very fast but, again, do you really want to ride like this on the way to the office?" - Jon Urry

"The new ZX-6R feels heavy but once it got going on the track I soon forget any extra lard as the handling was hard to fault. The slipper clutch meant I could back-shift as early as I liked and the rear tyre would still follow any bumps or undulations. I was well impressed and understand why this bike is already winning races at world level." - Niall Mackenzie

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