2003 Kawasaki ZX-6R & ZX6-RR

Thirty years after the legendary Z1 motorcycle, Kawasaki comes out swinging with a fresh pair of 600cc sportbikes

Why do midsize sportbikes live under a 599cc ceiling when most live out their lives wearing license plates instead of number plates? Kawasaki has fresh answers for that question in the form of two all-new 600s. First, there's this 636cc ZX-6R for the masses, blessed with a dollop of extra displacement for more useable horsepower just like the 2002 Euro-spec 636 that never made it Stateside.

Then, for you ambitious sods who really are going racing, the limited-edition ZX-6RR shuffles cylinder dimensions within the same all-new engine architecture to stay 600 Super-sport-legal, then adds a couple of tricks of its own. The good news is that both bikes are basically the same; the standard-spec 636 comes with 95 percent of the trickery of its more exclusive little brother.

Valve caps and fuel-tank lettering are the same. Otherwise, all resemblances to Kawasaki's '02-spec 600s are nil. Vague visual and mechanical R6 allusions, however, are clear. Although hard numbers are elusive in this preproduction world, the new ZX-6R is noticeably more compact than its predecessor. We figure it'll come in at least 10 pounds less than the current-spec, 435-pound (wet) ZX-6R. Every other facet of the '03 assembly aims at creating a sharper sporting package.

The ergonomic equation is take-no-prisoners compact: less room for gangly arms and legs. Inside the cockpit, modern electronics compress instrumentation into one round LCD instrument pod. The digital speedometer is surrounded by a bar-graph tach, complete with a tantalizing, 15,500-rpm redline. Moving beyond the typical array of idiot lights, 6R instrumentation includes a shift light--programmable from 12,000 to 16,000 rpm--to signal the rev limit's imminent arrival. There's also a stopwatch--triggered by new handlebar switch gear--that can remember your last 99 laps on track day.

Right now, chassis specifics are limited to what you can see, though the good news is that both bikes share the same basic bones. The new twin-spar aluminum chassis looks lighter and more rigid than before. Braking and suspension bits are clear signals that Kawasaki aims to build its most heart-attack serious 600s ever. The 41mm Kayaba fork is the first inverted unit on a modern Japanese 600. Now look at the brakes: Radial-mount calipers--big news on the racetrack a little over a year ago--are standard equipment. In theory, aligning caliper and rotor in this radial arrangement increases stopping power by cutting the inherent flex of a standard setup and allowing a more rigid caliper design. Each four-pot Tokico front caliper pushes four brake pads instead of the usual two, theoretically turning more leading edges against the rotor into more stopping power.

The 636cc heart of the matter grows from 599cc by adding 2mm to its immediate ancestor's 66mm bores and sticking with the same 43.8mm stroke. The cylinder head itself rides 10mm lower, and gets intake and exhaust valves that are 10mm shorter. Crankcases and assorted supporting structures are shorter, too. A single NACA-style duct feeds the fuel-injected fire--no more carburetors--funneling incoming atmosphere straight through the steering head, which is much more efficient than bending two ducts around it. Although cam-timing specifics are predictably murky, adjustable sprockets on the cams themselves are more compact, and there's less lift for more power at five-digit rev levels.

Kawasaki is betting big chips on its new midsize arsenal. The venerable ZX-6E is back for an encore as the ZZR600; it's a half-size bookend to the '02 ZZ-R1200. The 6R will also be very competitively priced at $7,999. Beyond that, production numbers for the '03 ZX-6R--including its racier RR sibling--will jump 50 percent from last year's levels. Only time and real test bikes will tell us how well that bet plays out, but one thing's for sure: This is prime time to be in the market for a new 600.

Aimed at earning Kawasaki some AMA and FIM 600 Supersport titles, the ZX-6RR is a limited-production version of its 636cc 6R brother. And though displacement (599cc) is subject to the racing rule books, it shares all-new engine architecture with the 636. Pairing a 67mm bore and a short, 42.5mm stroke, identical to the 2002 Honda CBR600F4i and Suzuki GSX-R600, the 6RR has its share of internal combustion trickery.

Despite their larger circumference, each forged piston is five grams lighter than a '02 ZX-6R slug. Longer rods let the pistons spend more time at bottom dead center, providing more time to inhale and burn incoming combustibles. Longer rods also mean less thrust/frictional losses against the front and rear of the cylinder wall doing the internal combustion dance.

There's a back-torque-limiter clutch to cut hop/skip/jump behavior under racy, precorner downshifting, and a comprehensive racing kit on the '03 accessory list. Otherwise, the limited-edition RR is blissfully similar to the mass-market 636. Exactly how limited it will be remains to be seen. Kawasaki says there will something less than one RR for each of its U.S. dealers, which translates into something less than 1000. The price? $8,399--$700 more than last year's ZX-6R, but $200 less expensive than Honda's full-fledged CBR600RR. Decisions, decisions...