Road Test

Splitting Heirs: Kawasaki ZX-6R 2005 v 2007

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?




Which 6R takes your fancy?

KAWASAKI'S ZX-6R has a reputation of being a seriously banzai machine. Fast, uncompromising, and focused, you can forget about user-friendliness: the 6R is all about buzzsaw action. Take the motor for a start. Raw, rev hungry and - for its size - very powerful. To be fair, that's been due in no small part to the 636cc engine, an unnatural advantage when it comes to comparisons with other 'true' 600s. Call that an 8bhp advantage over the rest of the pack, you'd have to be seriously useless to waste that advantage on the road or track. And given the latest generation ZX-6Rs from the 2003 B1H onwards have a sharp chassis and state of the art suspension and braking packages, that advantage hasn't been wasted.

Well, that was then. Now is 2007, and as of this year the ZX-6R no longer has that 36cc advantage. Kawasaki have pulled their neck in so the ZX-6R is now 'just' 599cc - yes, fully supersport-rules legal (and we're overlooking the RR homologation specials of the recent past here). Now the '07 also has to come fitted with the full monty in emissions clean-up kit, as per Euro3. Catalytic converters, Lambda sensors, ECU-governed throttle responses, all of that bloody mess which is clogging up the latest range of superbikes. All that clobber weighs a fair bit, making the new, smaller, ZX-6R some six kilos heavier. And of course that paraphernalia does a fair job of blunting performance.

That sets the context of this Splitting Heirs. Can the new '07 ZX-6R stand any chance of beating its '05 predecessor? It's got to be a big ask.

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 (24û as against 25û) 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.

PERFORMANCE

So here's the thing. On the road there's very little in it, it was almost uncanny how similar the engines felt. And given that you're hard pressed to belt along doing the wrong side of 12,000rpm for any prolonged periods the 636 had a hard time asserting any real advantage. You could tell yourself the 636 was pulling stronger off the bottom and through the midrange, but look in the mirrors and the 600 was always right there. You'd be a bloody fool to think that 2.5bhp would make any discernible difference on the road.

Curiously, when it came to handling, you liked best what you just got off. The 636 would feel fiendishly quick steering, too much so, until you swapped to the 600 - only to register that the newbie felt too ponderous. In reality neither are slow or bad handling, we're just talking relative nths here.

Where we found a real measurable difference was in lap times. We set a baseline lap with the '07 bike of 58s. We have to say it felt utterly crisp: turn-in, mid-turn, hooking up, revving out. You could totally understand the euphoria that accompanied its world launch. Then we took the 636 out and for three laps it felt the worst bike to ever venture onto a track. Then it transformed. The tyres came in and the 636 rocketed. It wasn't as measured as the 600; the bars would noticeably shake when accelerating hard out of Clearways and that rapid steering wasn't always easy to work, input-wise. But the surprise was the lap times. A full two seconds a lap quicker at 56s, and this on the Indy circuit too. So we took the '07 back out and batted it that bit harder. We closed the gap to a second, but that next second wasn't going to come without an incomparable extra level of effort. No, ridden like for like the 636 was a full second a lap quicker.

LOOKS

Here the feeling is unanimous - the new 600 simply beats the pants off the 636 on looks. Kawasaki have called the new look MotoGP inspired and that's as maybe. But the truth is they've made the 600 into one of the sleekest, most together-looking machines in the class. Just look - they've painted it bright orange and it still oozes class. The old 'un simply looks blocky and flat sided by comparison.

And the redesign has gone deeper than the flesh. Kawasaki have at last abandoned the techy but utterly illegible digital dash. This year it's a neat white faced analogue tacho and an easy read digi speedo. Simple, effective. And they've managed to hide the shitty cats and lamdas in the belly pan too. Good job. Some might lament the considerable withering in the passenger accommodation, but Kawasaki have been unabashed as labelling the ZX6R 'the ideal 600-class circuit machine', 'the ultimate middleweight track tool' - yeah, we get the message.

CONCLUSIONS

As per the ZX-10R Splitting Heirs (August issue) so in this case has another old ZX-R won over the new. It beats it on power, weight, speed and lap times. That's almost a full house. Does the '07 bike's wins on aesthetics and 'feel' really count for much?

Well, here's the thing. Honestly, Kawasaki have done a good job on making the new ZX-6R as good as it is. This Euro3 business is far harder to satisfy than any of us give credit to. Kawasaki didn't make the new bike five kilos heavier because they could. No, they went about lightening the bike, working on mass centralisation, doing everything they possibly could to mask the fact they were having to strap kilo upon kilo of emissions gubbins - effectively deadweight - onto what should be a superlight no-nonsense machine. And given that cats suck power as effectively as an 18-stone rider, then it's a triumph that combined with a 36cc capacity reduction Kawasaki have got as close as they have to the performance of the old bike. Once any self-respecting owner has put on an exhaust and Power Commander, the gap between the two bikes will be all but closed.

SECOND OPINION - OWNERS
GARY FILLINGHAM
TONBRIDGE, KENT
2005 ZX636

"I love my 636, it's got just enough of everything. It goes everywhere you want it to go, at your speed. It's not too scary. I had a GSX-R1000 K1 and that was a bit heavier, more powerful, just a bit frightening. I went for a test on a ZX-10R but the sales guys said I should ride this. I came back with such a big grin on my face - that was it.

I've been to Magny Cours on it for the French GP and done five track days now. It's actually very comfortable and on the seven hour run to Magny Cours it was fine. There is actually reasonable space between the pegs and the seat.

If I'm on the road, I can keep up with GSX-R750s okay. I like the way the 636 makes enough power at 7, or 8,000rpm, so you can pick up the pace without having to run down the gears. The B1, the earlier model I thought was more of a race bike. This one I think is more of a compromise.

The '07 I wouldn't buy. The 636 is a better pick for everyday use."

JONATHAN PETTIT
MAIDSTONE, KENT
2005 ZX636

"I'm new to bikes, a late starter. I bought the 636 on a bit of a whim. I liked the look. It had the performance. My son was born soon after so I don't get to ride as often as I'd like, which is why I've only done 3,000 miles. I was very happy with the 636 until I got to ride a new CBR600RR - and I found that to be just so refined, very comfortable and less edgy.

I got to ride the '07 ZX6R and was surprised how different it feels. The engine is similar but the handling is really very different. It seems slower to steer, I think they've steadied it up. But I've got a feeling it might be a CBR for me next. "

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


SPECS - KAWASAKI

TYPE - SUPERSPORTS

PRODUCTION DATE - 2005

PRICE NEW - £7245

ENGINE CAPACITY - 636cc

POWER - 109bhp@13,800rpm

TORQUE - N/A

WEIGHT - 193kg (WET)

SEAT HEIGHT - 820mm

FUEL CAPACITY - 17L

TOP SPEED - 163mph

0-60 - n/a

TANK RANGE - N/A

SPECS - KAWASAKI

TYPE - SUPERSPORTS

PRODUCTION DATE - 2007

PRICE NEW - £7190

ENGINE CAPACITY - 599cc

POWER - 106.6bhp@13,500rpm

TORQUE - N/A

WEIGHT - 199kg (WET)

SEAT HEIGHT - 826mm

FUEL CAPACITY - 17L

TOP SPEED - 155mph

0-60 - n/a

TANK RANGE - N/A

Kawasaki's ZX-6R has a reputation of being a seriously banzai machine. Fast, uncompromising, and focused, you can forget about user-friendliness: the 6R is all about buzzsaw action. Take the motor for a start. Raw, rev hungry and - for its size - very powerful. To be fair, that's been due in no small part to the 636cc engine, an unnatural advantage when it comes to comparisons with other 'true' 600s. Call that an 8bhp advantage over the rest of the pack, you'd have to be seriously useless to waste that advantage on the road or track. And given the latest generation ZX-6Rs from the 2003 B1H onwards have a sharp chassis and state of the art suspension and braking packages, that advantage hasn't been wasted.

Well, that was then. Now is 2007, and as of this year the ZX-6R no longer has that 36cc advantage. Kawasaki have pulled their neck in so the ZX-6R is now 'just' 599cc - yes, fully supersport-rules legal (and we're overlooking the RR homologation specials of the recent past here). Now the '07 also has to come fitted with the full monty in emissions clean-up kit, as per Euro3. Catalytic converters, Lambda sensors, ECU-governed throttle responses, all of that bloody mess which is clogging up the latest range of superbikes. All that clobber weighs a fair bit, making the new, smaller, ZX-6R some six kilos heavier. And of course that paraphernalia does a fair job of blunting performance.

That sets the context of this Splitting Heirs. Can the new '07 ZX-6R stand any chance of beating its '05 predecessor? It's got to be a big ask.

Kawasaki ZX-6R Review - 2/3

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.

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

Kawasaki ZX-6R Review - 3/3

PERFORMANCE

So here's the thing. On the road there's very little in it, it was almost uncanny how similar the engines felt. And given that you're hard pressed to belt along doing the wrong side of 12,000rpm for any prolonged periods the 636 had a hard time asserting any real advantage.

You could tell yourself the 636 was pulling stronger off the bottom and through the midrange, but look in the mirrors and the 600 was always right there. You'd be a bloody fool to think that 2.5bhp would make any discernible difference on the road. 

Curiously, when it came to handling, you liked best what you just got off. The 636 would feel fiendishly quick steering, too much so, until you swapped to the 600 - only to register that the newbie felt too ponderous. In reality neither are slow or bad handling, we're just talking relative nths here.

Where we found a real measurable difference was in lap times. We set a baseline lap with the '07 bike of 58s. We have to say it felt utterly crisp: turn-in, mid-turn, hooking up, revving out. You could totally understand the euphoria that accompanied its world launch. Then we took the 636 out and for three laps it felt the worst bike to ever venture onto a track.

Then it transformed. The tyres came in and the 636 rocketed. It wasn't as measured as the 600; the bars would noticeably shake when accelerating hard out of Clearways and that rapid steering wasn't always easy to work, input-wise.

But the surprise was the lap times. A full two seconds a lap quicker at 56s, and this on the Indy circuit too. So we took the '07 back out and batted it that bit harder. We closed the gap to a second, but that next second wasn't going to come without an incomparable extra level of effort. No, ridden like for like the 636 was a full second a lap quicker.

LOOKS

Here the feeling is unanimous - the new 600 simply beats the pants off the 636 on looks. Kawasaki have called the new look MotoGP inspired and that's as maybe. But the truth is they've made the 600 into one of the sleekest, most together-looking machines in the class. Just look - they've painted it bright orange and it still oozes class. The old 'un simply looks blocky and flat sided by comparison.

And the redesign has gone deeper than the flesh. Kawasaki have at last abandoned the techy but utterly illegible digital dash. This year it's a neat white faced analogue tacho and an easy read digi speedo. Simple, effective. And they've managed to hide the shitty cats and lamdas in the belly pan too. Good job. Some might lament the considerable withering in the passenger accommodation, but Kawasaki have been unabashed as labelling the ZX6R 'the ideal 600-class circuit machine', 'the ultimate middleweight track tool' - yeah, we get the message.

CONCLUSIONS

As per the ZX-10R Splitting Heirs (August issue) so in this case has another old ZX-R won over the new. It beats it on power, weight, speed and lap times. That's almost a full house. Does the '07 bike's wins on aesthetics and 'feel' really count for much?

Well, here's the thing. Honestly, Kawasaki have done a good job on making the new ZX-6R as good as it is. This Euro3 business is far harder to satisfy than any of us give credit to. Kawasaki didn't make the new bike five kilos heavier because they could.

No, they went about lightening the bike, working on mass centralisation, doing everything they possibly could to mask the fact they were having to strap kilo upon kilo of emissions gubbins - effectively deadweight - onto what should be a superlight no-nonsense machine. And given that cats suck power as effectively as an 18-stone rider, then it's a triumph that combined with a 36cc capacity reduction Kawasaki have got as close as they have to the performance of the old bike. Once any self-respecting owner has put on an exhaust and Power Commander, the gap between the two bikes will be all but closed.

Kawasaki ZX-6R Specifications

2005 KAWASAKI ZX-636R

PRICE NEW - £7245
ENGINE CAPACITY - 636cc
POWER - 109bhp@13,800rpm
WEIGHT - 193kg (WET)
SEAT HEIGHT - 820mm   
FUEL CAPACITY - 17L   
TOP SPEED - 163mph   

2007 KAWASAKI ZX-6R

PRICE NEW - £7190
ENGINE CAPACITY - 599cc
POWER - 106.6bhp@13,500rpm
WEIGHT - 199kg (WET)
SEAT HEIGHT - 826mm
FUEL CAPACITY - 17L
TOP SPEED - 155mph

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