2023 Kawasaki Ninja ZX-4RR First Ride

[Hugh Janus]

After 30-plus years of waiting, finally getting to throw a leg over a 400cc inline-four. (Kevin Wing/)

I first became obsessed with sportbikes in the late 1980s and early ‘90s; the plastic-clad repli-racers from Japan ruled the streets around my newfound home of Los Angeles. Suzuki GSX-Rs, Kawasaki ZX-7Rs, FZRs, CBRs roamed the streets in packs barking out of their Vance & Hines exhausts. But because it was LA, mixed in among them were some unicorns: Japanese-market 400s that somehow were imported through the gray market.

The September 1990 issue of Cycle World featured all of the forbidden fruit 400cc Japanense models that would never come to the US. (Cycle World Archives/)

These were the rarest of birds, and of course all the more desirable because of it. At the time, in the land of the rising sun, the All Japan TT-F3 championship spawned a technology war that had the four Japanese companies building insanely trick 400cc inline-four-powered sportbikes to be homologated for racing. Bikes like the Honda CBR400R (and later the Honda VFR400R), Suzuki GSX-R400, Yamaha FZR400RR SP, and of course the Kawasaki ZXR-400R, were pushing production bike technology to even higher levels. But the US market was ignored, buyers here wanted 750s and liter bikes, and importers didn’t feel Americans would pay a premium for the small-displacement models.

Kawasaki’s Ninja ZX-4RR was a welcome surprise for 2023. (Kawasaki/)

In short, I missed out. I was never lucky enough to throw a leg over one of these tiny canyon dancers, and passed on buying a Yamaha FZR400 in favor of a less expensive FZR600. So, when Kawasaki recently announced that it was not only reviving the 400cc inline-four, but bringing it to the US, internal bells went off in my head. Must. Ride. This. Bike! But why all the excitement?

Engine

The jewel at the heart of the Ninja ZX-4RR is undoubtedly the engine. The liquid-cooled DOHC 16-valve inline-four displaces 399cc and has a 57.0 x 39.2mm bore and stroke. Inside that engine is a lot of technology that Kawasaki has learned racing its ZX-6R and ZX-10R platforms. The aluminum die-cast cylinders have bores that are chrome-composite plated for reduced friction and better durability. The oversquare bores allow the use of large 22.1mm intake and 19mm exhaust valves for good airflow, while the short 39mm stroke allows high-rpm performance with a near-16,000 rpm redline. Forged camshafts actuate valves with triple-rate springs capable of dealing with the high rpm attainable by the engine.

The 399cc inline-four that powers the ZX-4RR revs to 16,000 rpm and makes peak torque at 11,000. US models have reduced peak power due to sound emission restrictions. Boo! (Kawasaki/)

Lightweight cast-aluminum pistons and case-hardened connecting rods contribute to quicker-climbing revs as does a lightweight flywheel. The compression ratio is set at 12.4:1. Like its big brother the 10R, the 4RR gets two-stage machining on the fine-sand cast intake ports for straighter more efficient airflow into the combustion chamber. Precision machined combustion chambers and narrow included valve angles ensure high-performance efficiency. Ram induction jams pressurized air into the airbox and then through dual-length intake funnels (that help flatten the torque curve) before passing into a bank of 34mm electronic throttle valve throttle bodies.

There is virtually nothing in this displacement category that compares to the Ninja ZX-4RR. (Kevin Wing/)

Downstream is a 4-into-2-into-1 exhaust system with linked header pipes for improved low-to-midrange performance. Exhaust gases then pass into the long traditional-style silencer equipped with three catalyzers. Speaking of sound, our US-spec bikes, as you may have heard, don’t have the same performance specifications as the European bikes. Our European correspondent informed us that the UK press kit lists power at 77 hp (without ram air), and 80 hp (with ram air). Talking to Kawasaki at the press launch we learned that the 4RR wouldn’t meet US sound-emission requirements, which in turn meant the engine has been neutered up top to do so. Our press kit just lists the torque at 26.5 lb.-ft. At 11,000 rpm with an intentional omission of horsepower figures. We’ll come back to this later.

The long traditional-style exhaust is equipped with a trio of catalytic converters. (Kawasaki/)

The last of the mechanical details to discuss in terms of the powertrain is the assist and slipper clutch that passes drive into the six-speed transmission. On the assist side, the clutch utilizes the rotational forces of the pressure plate so that when it exceeds the rotational force of the hub it engages the assist cams which in turn increase the pressure on the friction plates, making the pull at the lever lighter. While under hard deceleration it reverses to provide slipper functionality to prevent rear-wheel hop entering corners.

Electronics

As mechanically sophisticated as those 400s from the late ‘80s to early ‘90s were, the electronic revolution that we’re currently in the midst of was still 30 years in the future. In this day and age, rider aids are the norm and the new ZX-4RR has its share to give the rider some peace of mind.

Whereas many of the new superbikes have electronic intervention for just about everything, the 4RR keeps it simple with four integrated riding modes including Sport, Road, Rain, and Rider (manual settings). The first three of these have preset traction-control and power settings. In Sport you get KTRC setting 1 (of three) and Full power, in Road you get TC 2 and Full power, while Rain gives TC 3 (max) and Low power. In the Rider mode you can customize the settings and choose any traction-control setting or turn it off, and choose between Full or Low power. Standard on the ZX-4RR is the Kawasaki Quick Shifter that allows clutchless up and downshifts.

The 4.3-inch TFT display has multiple modes, including Street, Track, Black, or White options. | (Kevin Wing/)

The rider interface to access these settings is anchored by a 4.3-inch full-color TFT display that allows the rider to choose between two modes, either a more road-oriented view or a circuit mode that also can display a lap timer. The user can also choose between a black or white background, while the screen automatically adjusts its brightness based on ambient lighting conditions.

LED headlights, and front-fairing embedded turn signals are used up front, while slim LED rear signals are clean and attractive. Another electronic feature is smartphone connectivity via Kawasaki’s Rideology app, that allows users to tether to the bike via Bluetooth and access things like GPS route information, call notifications, vehicle info and even change settings from the phone.

LED headlights and fairing integrated turn signals keep the front clean. (Kevin Wing/)

Chassis

If the little 400cc engine is like a gem, the chassis that houses it is equally precious. What separates it from anything else in this displacement category are the high level of suspension and braking components.

Starting with the suspension, the 4RR utilizes a Showa Separate Function Big Piston fork in the front. Unlike all of the competition, this fork not only allows compression and rebound damping (both circuits in the right leg), but also has provision for preload adjustment which can be made on the left tube. The large-diameter damping piston is claimed to provide smoother action initially in the stroke with reduced stiction. All adjusters are on the top of the fork tubes for easy access.

Like the fork, the Showa Balance Free Rear Cushion (BFRC) shock is fully adjustable, with rebound, compression and preload. Its Horizontal Back-link design features a linkage on top of the swingarm, which Kawasaki says helps keep the shock away from the exhaust and engine to reduce the chance of it getting cooked and affecting performance.

The Ninja ZX-4RR has some serious hardware up front, with a fully adjustable Showa SFF-BP fork, and serious brake hardware. (Kevin Wing/)

A quick glance at the front end reveals a pair of Nissin four-piston radial-mount Monoblock calipers and 290mm discs, while a single-piston Nissin caliper and 220mm disc reside at the rear. The bike comes standard with Nissin ABS. Almost every other motorcycle on the market in this displacement category relies on a single caliper and disc up front. Five-spoke cast aluminum wheels are mounted with 120/70-17 and 160/60-17 Dunlop Sportmax GPR-300 rubber.

A fully adjustable Balance Free Rear Cushion shock is mounted to a link above the swingarm, which keeps it away from engine and exhaust heat. (Kevin Wing/)

The frame itself, to which all of these components mount, is a steel-trellis unit made up of various diameter and thickness tubing to provide the strength and flex that engineers were looking for. Like the main frame, the swingarm is made from steel, but has been arched on the right side to allow the exhaust silencer to be routed as high and tight as possible. A steel subframe is integrated into the main frame—not bolted on—which could be a consideration for those racing (and crashing) the bike on track. A couple other notable features that may get overlooked, are details like the five-position adjustable clutch and brake levers, and nice quality aluminum footpegs.

The trellis-style frame is made of high-tensile steel as is the curved swingarm and integrated subframe. (Kawasaki/)

Wheelbase measures a compact 54.3 inches, which for comparison sake is almost an inch shorter than the ZX-6R (55.1 inches) and considerably shorter than the 57.1-inch ZX-10R. Front end geometry measures 23.5 degrees of rake with 3.8 inches of trail, which is very similar to the 6R. Claimed curb weight is just under 415 pounds when topped up with 4 gallons of fuel. Seat height is 31.5 inches, which should accommodate a wide range of riders.

Riding Impression

Our day on the 4RR would be spent exclusively on Thunderhill Raceway near Chico, California. If you aren’t familiar with T-Hill, it’s basically a motorsport roller coaster slapped into the rolling hills of California’s nut farms. Blind crests, fast sweepers, a few tight chicanes, and ideal for the 4RR, a reasonably short front straight. Interestingly, Kawasaki decided that we’d be running the stock Dunlops for the day instead of track-oriented rubber, which at first sounded crazy as we’d also been told we’d get seven (!) 30-minute sessions.

Heading toward Thunderhill’s turn 9E drop. (Kevin Wing/)

Thunderhill definitely requires a bit of a learning curve to get up to speed on. Not only are there a bunch of blind crests as mentioned, but some off-camber ones as well. With way more than enough track time, getting up to speed and finding reference points wasn’t going to be a problem. While T-Hill’s signature turn 5E is borderline novelty as you crest a giant blind mountain and then plunge off the backside into an off-camber right (à la Laguna’s Corkscrew), it’s turns 6E to 9E that proved to be insanely fun on the 4RR. These three fast lefts are very reminiscent of Misano’s 11, 12, and 13, when they used to run the track counterclockwise.

Smaller-displacement bikes are incredibly rewarding on the track, and force you to be sharp and precise as you don’t have heaps of horsepower to mask your bad lines and mistakes. Keeping the ZX-4RR on the boil without losing momentum is ridiculously fun as you link everything together. One of the single best things about the 4RR is that it buys you tracktime. Whereas wrestling a 1,000cc-plus superbike around is exhausting, you feel like you can lap all day long on the little Kawasaki, which is what we did.

The great thing about lapping a 400 like the Ninja ZX-4RR is that you can ride all day and never get tired! (Kevin Wing/)

With the layout locked into memory and references burned into the brain, concentrating on the bike became easier. The first thing that leaps out at you is how good the brakes are. They honestly have the bite and feel of much more expensive Brembos that are found on most European sportbikes. There are only a handful of hardish braking zones at Thunderhill, and with the much slower speeds generated on the 4RR you don’t exactly hit your markers at warp speed, but one- and two-finger braking was no big deal getting it slowed from 120 to 125 mph.

Of course, the next most notable attribute of the little Ninja is the handling. In this regard, T-Hill was an ideal choice of venue for the bike to strut its stuff. Flicking the bike through the tighter corners makes you really appreciate what riding a small-displacement sportbike is all about, with very easy transitions side to side and the ability to alter your lines as needed midcorner. But what’s even more fun is being absolutely tapped through fast sweepers and yet not carrying so much speed as to have to worry about going into a lunar orbit if it all goes wrong. It’s here that we have to give a serious shoutout to the stock Dunlops, which even at the end of the day had proven to hold up quite well. For sure, running standard street tires makes you keep a bit in reserve, but the fact that they held up to three and a half hours of track time on a near-90-degree day further strengthens the argument for making a 4RR your trackday bike. It’ll save money on the tire bill for sure.

The TFT display has a track mode that also incorporates a lap timer and displays just the info you really need at a glance while riding on the track. (Kevin Wing/)

Another area that was impressive, is the ride quality of the suspension. Settings were left alone for the most part during the course of the day, as the bike was set up with recommended track settings suggested by our Kawi support crew. It was plush and forgiving and yet provided a good balance for just about everything encountered. Under braking for the hardest braking areas at turns 1E, 10E, and 14E, the fork was supportive and trustworthy, while the chassis and suspension handled cutting the bumpy rumble strip in the turn 11 chicane without issue.

So, the next area to address is the engine, especially knowing that our US market machines aren’t pumping out the same power as the bikes do in Euro trim. For sure, on a few of the longer straightaways the 4RR feels really soft up top, where in theory it should be pulling its hardest. But with that being said, the engine is surprisingly flexible exiting corners and has more bottom-to-midrange power than you might expect. The part of the rev-range that Kawasaki had to neuter is basically from 11,000 to 15,000 rpm, exactly where you really want to hear this thing scream.

Of course there is an easy solution from the aftermarket, and in particular from Graves Motorsports, who has found as much as 80 rear-wheel horsepower with a Supersport-spec build. But if you’re looking to just get back what the DOT has stolen from it, a flashed ECU and slip-on silencer nets a claimed 37 percent increase in peak power (over our US spec), and can be ordered from Graves Motorsports. If closed-course track riding is your planned destination, this seems like a no-brainer.

In this cockpit view, you can see the easy to access adjusters on top of the fork tubes. (Kevin Wing/)

With a limited amount of muscle on tap, keeping the bike in the Full power setting with minimal to no TC was easily the choice. Early in the day other settings were tried, some of which might be great on the street, but for the track we wanted everything it could offer. Performance from the quickshifter was good and helped keep the engine in its sweet spot, which is between 9,000 and 11,000 rpm before it hits the emission police’s cliff.

Conclusion

After a full day of lapping the ZX-4RR, we walked away very impressed with the bike’s chassis and in particular the quality of components that Kawasaki has fitted it with. When you look at this displacement range there simply isn’t anything else on the market like the Ninja 4RR except for the odd Chinese bike like Kove’s 450RR. The rest of the bikes in this displacement category are either singles (KTM RC 390) or parallel twins ranging from 300 to 500cc (Yamaha YZF-R3, Honda CBR500R, and so on) and just weren’t built for maximum performance, either in terms of engine performance or off-the-showroom-floor chassis capability.

As rare as 400cc sportbikes were in the ‘80 and ‘90s, they were thought to be completely extinct until Kawasaki’s Ninja ZX-4RR rose from the ashes. (Kevin Wing/)

From a performance standpoint, the Ninja ZX-4RR is an absolute blast on a racetrack, for sure it’s a shame that it had to be choked back by sound-emission regulations in the US market, but instead of holding that against Kawasaki, we’d prefer to give the green team kudos for reviving what was a long-lost formula to fun. And besides, like we said, restoring the top-end is a quick ECU flash away for those who plan to ride the bike at trackdays or plan on racing it.

It would be unfair to lump this bike in among the entry-level sportbikes on the market like those above, as it clearly is targeted toward a more experienced rider who appreciates the performance-oriented components and is willing to spend some extra coin to get them. Like those mentioned above, within its own family there is the Ninja 400 twin that starts at $5,299, but the $9,699 Ninja ZX-4RR is a totally different animal and actually quite a bargain for all of the features and top end components that it comes with. Technology has a price, and in this case that price isn’t too outrageous. So thank you, Kawasaki, at least for making one aging journalist’s long-lost desire to throw a leg over a 400cc screamer a reality. It was totally worth the wait.

Nice touches like the five-position adjustable brake and clutch levers are welcome. (Kevin Wing/)

A single-piston Nissin caliper and 220mm disc handle braking at the rear. (Kevin Wing/)

The Ninja ZX-4RR in its happy place. The racetrack. (Kevin Wing/)

Thunderhill couldn’t have been better for riding this little firecracker. (Kevin Wing/)

2023 Kawasaki Ninja ZX-4RR KRT Edition Specs

MSRP:	$9,699
Engine:	DOHC, liquid-cooled, inline-four; 4 valves cyl.
Displacement:	399cc
Bore x Stroke:	57.0 x 39.1mm
Compression Ratio:	12.3:1
Transmission/Final Drive:	6-speed/chain
Claimed Horsepower:	N/A
Claimed Torque:	26.5 lb.-ft. @ 11,000 rpm
Fuel System:	DFI w/ 34mm throttle bodies
Clutch:	Assist w/ slipper function
Engine Management/Ignition:	TCBI w/ digital advance
Frame:	Steel trellis
Front Suspension:	37mm inverted Showa SFF-BP fork, spring preload adjustable; 4.7 in. travel
Rear Suspension:	Showa BFRC Lite shock, fully adjustable; 4.9 in. travel
Front Brake:	Dual radial-mount, 4-piston calipers, 290mm discs w/ ABS
Rear Brake:	1-piston caliper, 220mm disc w/ ABS
Wheels, Front/Rear:	5-spoke cast aluminum; 17 in.
Tires, Front/Rear:	120/70-17 / 160/60-17
Rake/Trail:	23.5°/3.8 in.
Wheelbase:	54.3 in.
Ground Clearance:	5.3 in.
Seat Height:	31.5 in.
Fuel Capacity:	4.0 gal.
Claimed Wet Weight:	415 lb.
Company:	kawasaki.com

Gearbox

Helmet: Arai Contour-X

Suit: Alpinestars GP Plus V4

Gloves: Alpinestars GP Tech V2

Boots: Alpinestars Supertech R

Airbag: Alpinestars Tech-Air 5 System

Source

[Pedro]

For someone built like a racer, this must be a blast of a bike to ride, so ugly though.

[Marcel le Moose Fondler]

16 minutes ago, Pedro said:

For someone built like a racer, this must be a blast of a bike to ride, so ugly though.

Yes lime green isn't my favorite colour..

[Pedro]

Just now, Marcel said:

Yes lime green isn't my favorite colour..

I like the colour on sportsbike kawasakis, but that front end… 

[Buckster]

13 hours ago, Pedro said:

I like the colour on sportsbike kawasakis, but that front end… 

It will look different when Polaris copy it and call it an Indian. 

[Marcel le Moose Fondler]

On 07/07/2023 at 18:12, Pedro said:

For someone built like a racer, this must be a blast of a bike to ride, so ugly though.

Now that you mention it...the front end looks like Bucks head.