Kawasaki Broadcasts The 2023 Ninja ZX-4RR KRT

One of many worst-kept secrets and techniques in motorcycling is now a secret no extra: Kawasaki has introduced the Ninja ZX-4RR KRT can be coming to the US in 2023, (hopefully) ushering in a revival of 400cc four-cylinder sportbikes that had been all the craze within the Nineties. However in contrast to the present parallel-twin Ninja 400, which is basically a funds bike wearing sportbike garments,  this latest mannequin is worthy of the ZX prefix, because it boasts correct suspension, twin radial brakes, a full electronics suite, and chassis geometry impressed by its ZX-6R and ZX-10R siblings – oh, and let’s not neglect – a compact four-banger that may rev to over 15,000 rpm! However extra on all these issues in a minute.

Be part of the Kawasaki Ninja ZX-4R Discussion board

First, in the event you’re a longtime MO follower, this shouldn’t shock you. Our resident sleuth, Dennis Chung, broke floor on this new bike over a yr in the past – in Might of 2021, to be precise, when Kawasaki utilized for a patent for an air duct to drive air across the radiator and header pipes to assist cool the engine instantly. Dennis adopted that up in August of 2022 when Kawasaki filed VIN submissions for an upcoming ZX-4. Nonetheless, in an effort to convey Dennis’ non-existent ego again to Earth, let’s nitpick one little factor: He received the variety of Rs improper (for the US not less than – he nonetheless suspects a single R will come to different markets). The suffix ought to embody two Rs, together with three extra letters: KRT (Kawasaki Racing Staff). This suffix issues as a result of a double-R Kawasaki Ninja is supposed to be a thoroughbred observe weapon. 

Is it? On paper anyway, it certain appears so. With out additional ado, let’s take a better have a look at the long-anticipated Ninja ZX-4RR.


We will’t begin anyplace else however the engine. As you already know, it’s a 399cc, liquid-cooled inline-four with twin overhead cams. Bore and stroke measure 57.0 x 39.16mm, for an oversquare engine able to such excessive rpm. The ECU is much like the one on the Kawasaki Z H2, which permits for using Kawasaki’s newest electronics. Digital Throttle Valves (ETV) with 34mm throttle our bodies feed air and gasoline to the engine and in addition facilitate using all of the rider aids we’ve come to count on from in the present day’s sportbikes, like traction management, energy modes, and even the bi-directional quickshifter.

Wanting on the cylinder head, the consumption port interiors are sand solid, utilizing tremendous sand, which ends up in a easy end. Much like the Ninja ZX-10R, the consumption port exits have been machined in two phases, first together with the valve seats after which once more at an inclined angle, to create a straighter path for consumption air into the combustion chamber. This promotes a smoother circulate and a higher quantity of fuel-air combination. Light-weight solid camshafts contribute to the high-rpm efficiency. Triple-rate valve springs preserve the valves in verify, even at excessive rpm. 

The consumption valves themselves are massive, measuring 22.1mm, and are complemented by 19mm exhaust valves, flowing an amazing quantity of air crucial for top engine speeds. A slim valve angle of 24.8º not solely helps combustion effectivity but in addition helps in designing a compact cylinder head and total engine. The combustion chambers are precision machined to excessive tolerances – a manufacturing approach that’s restricted to Kawasaki’s high-performance premium fashions. 

The tiny little pistons are solid aluminum for low reciprocating weight and quick-climbing revs. Additionally, to assist obtain that lofty engine velocity, the piston skirts are comparatively quick and have a molybdenum coating for elevated sturdiness. Compression ratio is a modest 12.3:1, which Kawasaki says permits using “common gasoline.” We’re undecided if which means utilizing octane as little as 87 (not that we do anyway), however we are able to already see aftermarket tuners taking part in with compression ratios and ignition timing to reap the benefits of race gasoline. Using an aluminum die-cast cylinder with an open-deck design, glorious warmth dissipation and low engine weight is achieved. 

The Kawasaki press launch continues:

With a purpose to scale back mechanical loss and vibration, Kawasaki engineers rigorously chosen the connecting rod ratio, whereas a particular carburizing remedy was used on the connecting rods to enhance sturdiness and scale back weight. Because of the crankshaft’s mild flywheel mass, a low second of inertia was reached, contributing to a quick-revving engine character and direct throttle response. A deep oil pan ensures that the oil pump inlet is all the time submerged, blocking air from being ingested, even throughout arduous acceleration and deceleration whereas sport or observe using.

Radiator proven with elective radiator display screen.

Conserving the engine cool is clearly a excessive precedence, and the water jackets had been rigorously designed for this function. Even the long-reach spark plugs provide extra contact with the water jacket to assist stop engine knocking. There’s a big, 30-row radiator to maintain the coolant temps beneath management, and the patented air duct talked about on the prime of this story is definitely a radiator fan cowl that’s positioned behind the radiator to maneuver sizzling air out to the perimeters and away from the rider. Ducts constructed into the fairings funnel air in the direction of the radiator to convey coolant temps down.

A real “mini” superbike, the ZX-4RR has a practical ram air scoop on the entrance of its nostril, identical to its ZX-6R and ZX-10R siblings. Utilizing an identical format to the Ninja H2, the Ram Air duct is routed to the left of the entrance fork on its option to the airbox. This contributes to a duct with a extremely environment friendly airflow, enabling cool, high-pressure air from the entrance of the bike to be ingested. Moreover, the design is extraordinarily efficient at stopping water from coming into the airbox whereas using within the rain. And simply in case you neglect, the big Ram Air duct has “Ram Air” stamped into it. Perhaps you’ll be able to present it off to your pals…? 

The consumption funnels are 60mm and 40mm for environment friendly filling and produce a flat torque curve with easy energy supply. The downdraft consumption creates a shorter, extra direct path for consumption air to enter the cylinder, enhancing cylinder-filling effectivity and rising engine energy at excessive rpm.

After all of the spent gasses are completed combusting, they exit the bike by way of an exhaust system modeled after the ZX-6R. 4-into-one header pipes hyperlink headers 1-2 and 3-4 to assist with low-end torque, the pipes then meet with a collector with three catalyzers earlier than leaving by way of the lengthy silencer within the again. 

Placing the ability to the bottom is a six-speed gearbox with Help & Slipper clutch. The help operate clamps the clutch pack tighter whereas additionally offering a light-weight clutch, and the slip operate permits the clutch to slide slightly to stop rear-wheel hop within the occasion of a sloppy downshift. After all, you gained’t make any sloppy downshifts as a result of the ZX-4RR comes with a bi-directional quickshifter.

Finally, everybody needs to know what sort of energy it’s making. The reply is… we don’t know. Kawasaki has solely revealed that it makes a peak of 26.5 lb-ft of torque at 11,000 rpm. Our guess is peak energy can be round 40-50 hp. Nonetheless, we’re already excited on the energy the aftermarket will be capable to pump out of one in every of these. 

Chassis and Suspension

In contrast to its ZX-6R and ZX-10R brothers, the ZX-4RR doesn’t use a fringe beam body. As a substitute, there’s a metal trellis body of assorted pipe diameters and thicknesses to attain particular rigidity and chassis flex, using suggestions discovered instantly from the KRT World Superbike crew. What sort of suggestions? Issues like the middle of gravity place, swingarm pivot place, engine axis positions, and caster (aka rake) angle had been simply among the dimensions impressed by the ZX-10RR. The lengthy, metal swingarm permits for optimum entrance/rear weight distribution, whereas the arch design of the correct aspect not solely seems to be cool and attracts a steadiness between rigidity and flex, however it additionally provides the area wanted to suit the silencer as centrally as attainable.

Showa gives suspension for each Kawasaki’s World Superbike crew and its manufacturing fashions, and the ZX-4RR is the newest to profit from this collaboration. Within the entrance is Showa’s 37mm SFF-BP (Separate Operate Fork – Huge Piston) with spring charges and valving particularly for the mixed-use circumstances the ZX-4RR will see on the road and observe. Because the identify suggests, every fork leg separates the suspension features. The left tube handles preload changes, whereas the correct tube handles the damping adjustments. In contrast to a cartridge fork, nonetheless, the fork tube itself acts like a cartridge, permitting an even bigger piston for use. Therefore the identify. Sadly, the ZX-4RR falls quick in that it solely presents preload adjustment up entrance. Should you had been hoping to have the ability to change the compression or rebound settings, sorry. You’re hosed.

Nonetheless, on the rear is Showa’s BFRC (Stability Free Rear Cushion) shock mounted by way of linkage above the swingarm, inserting the shock additional away from the warmth generated from the engine and exhaust. The shock is much like the one on the ZX-10R however clearly tuned in another way for the smaller bike. In contrast to the entrance fork, the shock has adjustability for preload, compression, and rebound damping. 

As disappointing because the entrance suspension could also be (not less than on paper), the brakes on the ZX-4RR undoubtedly look acceptable for the half. Up entrance are two 290mm semi-floating discs paired with radial-mount, four-piston monobloc calipers, with the higher pistons measuring 32mm and the decrease ones 30mm. Right here’s hoping Kawasaki has given it sufficient brake pads, however even when not, these are simple sufficient to vary. The rear is a single 220mm disc with a single 38mm piston caliper. Kawasaki’s newest ABS expertise comes normal.

One other bit of fine information is the ZX-4RR’s star-pattern five-spoke wheels come inventory with Dunlop Sportmax GPR-300 tires. The entrance is a regular 120/70 dimension, and the rear is a 160/60, that means there are many distinctive tire selections. 

Then there’s the load. With a curb weight of 414.5 lbs, the ZX-4 is about 50 lbs heavier than the present Ninja 400 (361 – 366 lbs), and fewer than 20 lbs lighter than the ZX-6R (425 – 430 lbs). A sub-400-lb curb weight would have been good, however time will inform if it feels lighter than it really is.


On the floor, it appears foolish for a 399cc bike to have an electronics suite, however as a motorbike with two Rs in its identify, it does make extra sense. Plus, because the bike already has fly-by-wire throttle, the parts are already in place to include TC. Therefore, the ZX-4RR sees the KTRC system utilized right here. Adjustable in three completely different ranges (4 in the event you embody Off), Kawasaki fails to say something concerning an IMU in its press supplies, which leads us to imagine that it’s a reactive TC system as an alternative of a predictive one – which appears tremendous for a motorbike like this. 

Along with KTRC, the 4RR additionally will get two-level Energy Modes, and built-in Driving Modes (Sport, Street, Rain) with preset energy and TC settings. A fourth mode, Rider, is a handbook mode that permits you to set the ability and TC settings independently.

Info is displayed by way of a 4.3-inch TFT not too dissimilar from the one on the ZX-10R. Other than the usual menu that provides you highway velocity, engine velocity, and the like, there’s additionally a Circuit Mode display screen that reveals track-related info entrance and middle, together with a lap timer. There’s additionally the power to attach the ZX-4RR to Kawasaki’s Rideology App to view automobile information, using logs, cell phone notices, and extra.


In case you haven’t seen but, this can be a supersport bike, by way of and thru. Clip-ons are mounted beneath the triple clamp, and the pegs are barely behind you (although they don’t seem like too excessive within the photographs). You’re going to be within the racer place with weight over your wrists, which can be particularly obvious in the event you’re coming off, say, the present Ninja 400 and its comparatively upright bars. That mentioned, as we have a look at these photographs, the seat, which is 31.5 inches off the bottom (in comparison with the Ninja 400’s 30.9-inch seat top) seems to be cramped for average-size adults. The three.96-gallon tank, too, is slim, which is nice for feeling slim on the bike and for with the ability to put a foot down however may pose an issue relating to discovering an anchor level for the skin leg as you’re slicing by way of a flip.

Being a part of the ZX household, the resemblance to its greater siblings is placing, albeit anticipated. Traditional Ninja styling carries over to the ZX-4, with sharp, angled styling all through, capped off with the signature aggressive and angled nostril part and big ram air scoop borrowed from the ZX-6R and influenced by the previous-generation ZX-10R.

There’s One Huge Catch

To date, the ZX-4RR feels like a motorbike any sportbike fan can get behind, proper? Effectively, in the event you keep in mind, the 400cc four-bangers of 30 years in the past all disappeared as a result of they merely grew to become too costly for their very own good. The 2023 Kawasaki Ninja ZX-4RR KRT Version carries a retail value of $9,699. May we be on the verge of seeing historical past repeat itself?

For some perspective, that’s practically $4000 greater than the present Ninja 400 and solely $1000 lower than the bottom ZX-6R. Granted, as somebody who loves (and owns) small bikes, I’ll be the primary to say that the worth of the ZX-4RR shouldn’t be measured in horsepower. However with pricing so shut to larger bikes, one thing tells me the preliminary hype surrounding the ZX-4 will fade quick earlier than riders lust for horsepower once more. If there’s any hope for extra small-bore screamers to make their return, then Mr. Chung’s prediction of a Single R model coming right here with a cheaper price tag should come true. Time will inform. 

Within the meantime, there’s no denying we’re wanting ahead to throwing a leg over the Ninja ZX-4RR.

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