The 636cc iterations of the ZX-6R have always offered more response low down than its 599cc rivals, but it’s all relative: a simple 1mm overbore on a ‘true’ 600 doesn’t suddenly make it a torque monster.
The 599cc model is no longer sold, even for racing, with Supersport race regs tweaked with a balancing factor to make the disparate models on offer (the 599cc CBR600RR, the 765cc Triumph Street Triple RS and the 955cc Ducati Panigale V2 as well the Kawasaki).
The ZX-6R’s drive off the bottom is minimal until 4000rpm, where it perks up and gets going, rapidly building engine speed and hitting its prime at 13,000rpm, although the days of 600s head-banging their way to 15,000rpm or more are long gone: the new camshafts, headers and intake slow the top-end rush, and while it will rev out, it doesn’t do so in the same aggressive, addictive manner.
Yet, it doesn’t feel slow, and scrutinising both our dyno and speed test figures reveals why. It hits a top speed of ‘only’ 144mph (measured on a datalogger) but does so with ease, and more or less hits a brickwall. We’d expect a 600 to clear 150mph, based on the best figures from the class in its prime about 15 years ago.
Our first thought was that it’s now restricted at high rpm, but cross-referencing the dyno chart reveals it has no issue with revving out in sixth, and makes the same power (115bhp at the rear wheel) as it does in the lower gears, suggesting it’s geared unusually low for a production bike. Gearing is shorter than it might have once been: why, only Kawasaki knows (it may help with meeting noise/emissions standards at fixed speed/rpm, or it could just be to maximise enjoyment), but it’s a welcome change.
It’s a touch revvy at cruising speed, but it’ll hold a higher gear than you might imagine, and it’ll suit the UK’s nadgery parkland circuits really well, too. As an experiment, we tried taking off in sixth. It managed it… an astounding, if useless achievement for a 600…
The TFT screen and new fairing have a modern, quality feel, and the main chassis and running gear is a cut above bikes like the Aprilia RS660, Yamaha R7 and other more budget-friendly middleweight sportsbikes. Even Kawasaki’s own ZX-4RR is built to a lower standard, though it also £2000 cheaper.
Certain components and fittings will appear cheap next to the our favourite mid-class sports machine, the Street Triple 765 RS, which has top-notch finish as well as high-end componentry for not much more cash.
Reliability shouldn’t be an issue, as the engine is 11 years old if you trace it back to the first modern 636, with roots that trace back 15 years, with less propensity for high revs and the stresses that come with pinging a 600 off the rev limiter. We’d expect ZX-6R life to be trouble-free.