There are some bike genres that a manufacturer can almost certainly claim as its own. Honda is the firm that made the V-4 sportbike work, Ducati is the 90-degree V-twin and Triumph rules with its triples.
And there's a strong case to say Kawasaki invented the 600cc-sportbike class. Back in the mists of time, its KZ550 air-cooled sportsters began evolving into something more exciting; the GPz550 of 1983 was a stepping-stone to the GPz600R of 1985. Its 900cc big brother gets most of the kudos now, but the GPz600R was the first proper supersport 600. By "proper" we mean 16-valve water cooled engine, full fairing, sporty chassis and aluminum swingarm (the frames were still steel tubes for the moment). The GPz made about 85 hp, weighed in a touch over 400 pounds, and started off a long line of 600cc supersport bikes that ends up today in the form of the ZX-6R.
Today's ZX-6R is a pretty evolved creature. The first one appeared in 1995, a sportier version of the fast-but-flabby ZZR600 sport tourer, and while it didn't quite get the better of Honda's class-topping CBR600, it made a very worthy competitor to the likes of Yamaha's YZF600R and Suzuki's GSX-R600. Its main strength was a classic big K attribute: a wildy fast engine with a screaming top-end and bulletproof engineering. Kawasaki incorporated the ram-air technology from its ZZ-R range; as the ZX-6R went faster its airbox was filled with even more cool, dense air.
But lots of peak power and top speed dominance isn't the only measure of a bike, and the ZX-6R lost out a little in terms of chassis performance. It was still a little overweight, and while updates in 1998 and 2000 made it a much better bike, it was left behind by ever more radical improvements to the CBR600 and GSX-R600, as well as the appearance of Yamaha's R6 in 1999.
Kawasaki's entire range drifted from the late 1990s into the early 21st century, and for a time it looked like Team Green had all but given up on performance motorcycles.
The first signs of a Kawi comeback came in-where else-the 600 class. For 2002 the firm pulled off an audacious coup in the form of a big-bore 636cc version of the ZX. The simple step of replacing the old cast-iron cylinder liners with linerless aluminum bores offered a lot more space in the block, and Kawasaki bored the motor out like some deranged drag-strip nitro-head. All it had to do then was drop in some high-compression pistons to instantly turn the ZX-6R from the class clown to the class ass-kicker. Honda, Yamaha and Suzuki cried foul into their sake, but the lateral thinking (or was it desperation?) of the big K had them on the ropes.
And there was no let up a year later either when Kawasaki revealed it had been doing more than just buying up mail order big-bore kits. For 2003, we were treated to an incredible revamp of the midweight Ninja. Kawasaki just about threw the kitchen sink at the middleweight class, adding USD forks, radial brake calipers, ram-air and fuel-injection, then dressed it in a razor-sharp new suit of aerodynamic bodywork. Launched at the Sepang GP circuit in Malaysia, it was the first salvo from a newly serious Kawasaki, which was followed up by the ZX-10R a year later, then further refinements to the 600 Ninja.
Kawasaki dropped the 636cc capacity a few years back, and we think that's a shame. In the same way as Suzuki's GSX-R750 has something special, the extra 37cc on the Ninja made a real difference, lifting it ahead of the pack in terms of day-to-day usability and sheer grunt. For 2007, the Ninja was a plain 599cc machine again, and while it was damned good, it fell behind the crazy-assed R6 and the super-capable CBR600RR. The 2009 ZX-6R went back to basics: a strong engine and competent chassis with excellent suspension. These traits helped slot the Kawi right back in at the top of the 600cc pack.